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Large tow carbon fiber (LTCF) has excellent performance and low cost. However, there are still many difficulties in the application of LTCFs, among which the problem of interfacial penetration is mainly solved. Building interfaces with sizing structures of fiber composites is an effective approach to achieve high performance. In this article, a water-based epoxy sizing agent suitable for LTCF fiber thermoset composites was studied. A comparison of the five LTCFs in this study shows that the wettability and contact angle of the sized LTCFs are significantly improved. In addition, the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) increased from 52.3 to 71.0 MPa (35%) and 36.4 to 54.6 MPa (50%), respectively. Compared with other imported LTCFs, domestic large-size LTCFs have a wide variety and a large number of surface functional groups, thereby improving their wettability and covalent bonding with the resin matrix. This work has reference significance for the practical application and industrial production of LTCFRP. [ABSTRACT FROM AUTHOR]

The rapid development of hydrogen fuel cells has been paralleled by increased demand for lightweight type IV hydrogen storage vessels with high hydrogen storage density, which raises the performance requirements of internal plastic liners. An appropriate manufacturing process is important to improve the quality of polymer liners. In this paper, DSC, WAXD, a universal testing machine and a differential pressure gas permeameter were used to investigate the effect of the cooling rate of the rotational molding polyamide 11 on the thermal, crystallization, mechanical and barrier properties. The cooling rate is formulated according to the cooling rate that can be achieved in actual production. The results suggest that two PA11 liner materials initially exhibited two-dimensional (circular) growth under non-isothermal crystallization conditions and shifted to one-dimensional space growth due to spherulite collision and crowding during the secondary crystallization stage. The slower the cooling process, the greater the crystallinity of the specimen. The increase in crystallinity significantly improved the barrier properties of the two PA11 liner materials, and the gas permeability coefficient was 2-3-fold higher than at low crystallinity. Moreover, the tensile strength, the tensile modulus, the flexural strength, and the flexural modulus increased, and the elongation at break decreased as the crystallinity increased. [ABSTRACT FROM AUTHOR]

Advanced thermoplastic composites have garnered significant attention due to the advantages such as secondary thermoforming. In the case of thermoplastic composites based on semicrystalline polymers, the self-nucleation (SN) effect induced by repeated thermal cycling can greatly influence the crystallization behavior and mechanical properties of both the matrix and the composites. This study investigated the SN effect of carbon fiber reinforced polyphenylene sulfide (CF/PPS) composites and its impact on non-isothermal crystallization behavior by differential scanning calorimetry, polar optical microscopes and atomic force microscopes. The results revealed that a lower secondary melting temperature led to a higher crystallization temperature. Furthermore, the SN effect significantly improved the fiber/matrix interfacial interaction and mechanical properties of CF/PPS composites. This improvement was evident in the enhanced compression properties, interlaminar shear properties, and in-plane shear properties at different test temperatures. The study also proposed mechanisms for the improved fiber/matrix interfacial interaction and matrix mechanical properties through the SN effect. This work not only enhances our understanding of the changes in mechanical properties of CF/PPS composites due to matrix crystalline morphology changes during secondary thermoforming but also provides insights into improving the manufacturing efficiency and mechanical properties by selecting a low melting temperature to achieve a high crystallization temperature in secondary thermoforming. The influence of the thermoforming processes on spherulitic size changes the mechanical properties of thermoplastic composites. [Display omitted] • SN behavior in CF/PPS composites results in formation of nanometer-sized crystallites. • Nanometer-sized crystallites enhance the mechanical properties of CF/PPS composites. • SN behavior in CF/PPS composites accelerates the crystallization rate and raising T c. [ABSTRACT FROM AUTHOR]

This paper examines hybrid organic-inorganic polymer nanocomposites incorporating organically modified montmorillonite (MMT) and ultra-high molecular weight polyethylene (UHMWPE). UHMWPE/MMT hybrid nanocomposites were prepared using gel and pressure-induced flow (PIF) processing methods at a gel concentration of 8 wt.% UHMWPE with various organoclay contents (0,5,10,15, and 20 pphr). The interlayer properties of the nanocomposites were studied by X-ray diffraction (XRD) transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The thermal and mechanical interfacial properties of the nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and the use of a universal test machine (UTM). XRD and TWM indicated that the nanocomposites were formed upon dispersion of MMT in the polymer matrix. From the DSC, TGA and DMA results, we found that the thermal stability of the UHMWPE nanocomposites increased as the MMT content increased. The nanocomposites showed higher tensile strengths than those of pure UHMWPE gel sheet. These findings indicate that the interfacial and mechanical properties were improved by the addition of MMT and PIF processing. [ABSTRACT FROM AUTHOR]

Abstract: An exact linearity interrogation technique with enlarged dynamic range for fiber Bragg grating (FBG) sensor has been analyzed theoretically and demonstrated experimentally. The technique bases on two matched FBGs for receiving the reflected signal from the sensor FBG and two photodiodes (PDs) for collecting the reflected signal from the two receiver FBGs. The linear expression between the nature logarithm of the output ratio of the two PDs and Bragg wavelength of the sensor FBG is obtained on the condition that the bandwidths of the two receiver FBGs being equal to each other. The wavelength of the sensor FBG can be interrogated simply and accurately by the linearity technique according to the expression. In addition, a new tunable paralleled matched gratings interrogation scheme is proposed. The interrogation range can be enlarged and multiple FBG sensors can be interrogated simultaneously with the tunable interrogation scheme. [Copyright &y& Elsevier]

A temporary confinement of the quaternary tetramethylammonium tetrafluoroborate (TMA BF4) salt among polyamide molecules has been used for the preparation of aliphatic polyamide nylon 6,6 fibres with high-modulus and high-strength properties. In this method, the suppression or the weakening of the hydrogen bonds between the nylon 6,6 segments has been applied during the conventional low-speed melt spinning process. Thereafter, after the complete hot-drawing stage, the quaternary ammonium salt is fully extracted from the drawn 3 wt.% salt-confined fibres and the nascent fibres are, subsequently, thermally stabilized. The structural developments that are acquired in the confined-nylon 6,6 fibres are ascribed to the developments of the overall fibres' properties due to the confinement process. Surprisingly, unlike the neat nylon 6,6 fibres, the X-ray diffraction (XRD) patterns of the as-spun salt-confined fibres have shown diminishing of the (110)/(010) diffraction plane that obtained pseudohexagonal-like β' structural phase. Moreover, the β' pseudohexagonal-like to α triclinic phase transitions took-place due to the hot-drawing stage (draw-induced phase transitions). Interestingly, the hot-drawing of the as-spun salt-confined nylon 6,6 fibres achieved the same maximum draw ratio of 5.5 at all of the drawing temperatures of 120, 140 and 160 °C. The developments that happened produced the improved values of 43.32 cN/dtex for the tensile-modulus and 6.99 cN/dtex for the tensile-strength of the reverted fibres. The influences of the TMA BF4 salt on the structural developments of the crystal orientations, on the morphological structures and on the improvements of the tensile properties of the nylon 6,6 fibres have been intensively studied. [ABSTRACT FROM AUTHOR]

Thermal expansion molding process (TEMP) is a sophisticated molding technique for creating complex sandwich composites. The core key of TEMP is a high‐performance, thermally expandable resin film. In this study, the epoxy resin is used to create a specific crosslinking network that can provide the support force required for the stable molding of the vesicles during the expansion process of the foaming agent. The curing process of the resin was determined by analyzing the change in the exothermic amount of the epoxy resin during the curing process and the flow behavior of the resin. The pore size distribution of the epoxy foam was investigated, and the expansion force of the thermally expandable resin was tested. The TEMP molding process was compared with the vacuum bag press molding (VBPM) process. The TEMP molding technique increased tensile and compressive strength by about 25%, flexural strength by 34.5%, and shear strength by 54.5%. Finally, the section on microanalysis of the comparative materials and the short beam bending experiments of the sandwich structure provides a theoretical foundation for developing complicated sandwich structures. Highlights: Preparation of thermally expandable epoxy prepregs with stabilized foaming by means of pre‐curing.The effects of curing temperature, foaming agent content and expansion multiplicity on the thermal expansion force of epoxy prepreg adhesives were investigated.Thermally expandable epoxy prepreg molding composites with different expansion multiplicities and analysis of the mechanical properties of the composites.Preparation of foam core sandwich composites by thermal expansion in‐mold monolithic molding process and their verification by bending experiments. [ABSTRACT FROM AUTHOR]

This study developed a kind of non-woven carbon tissue reinforced adhesive film (NWCTRAF) with high bonding strength and reliability by interleaving the NWCT into the adhesive film. The manufacturing process, bonding strength, Weibull distribution, metallography of cross-section, and fracture surface morphology of NWCTRAF specimens were investigated. The results showed that the average bonding strength and Weibull characteristic strength (WCS) of single lap joint (SLJ) were 27.4a and 28.2 MPa, which increased by 17.6% and 15.1%, respectively compared with the blank specimen, and the Weibull modulus risen from 9.51 to 18.72, which indicated that NWCTRAF specimens had higher bonding reliability. The mechanism of micro-crack formation was obtained by analyzing the cross-section of loading 95% WCS without visible damage. The metallographic section showed that the microcracks of the blank specimen originated from the interface between carbon fiber-reinforced polymer (CFRP) and adhesive layer, while the microcracks of the NWCTRAF specimen originated from the resin-rich regions between the carbon fiber fabric layers in CFRP. Typical failure modes were gained from optical microscope and SEM. Failure modes of blank specimen included more interface failure of CFRP-adhesive and Al-adhesive, while NWCTRAF specimen had more carbon fiber tearing and delamination of CFRP. The fracture morphology of adhesively cohesive failure included the pull-out of short carbon fibers and the appearance of rough and multi-stage resin in the NWCTRAF specimen, which improved the toughness of the adhesive layer. The bridging effect of short carbon fibers in the NWCTRAF disperse and transfer stress to CFRP and fail at resin-rich regions of CFRP, decrease the bonding interface's direct failure, and improve the bonding strength and reliability. [ABSTRACT FROM AUTHOR]

Highlights: The influence of temperature parameters in two thermal cycles on the self-nucleation (SN) behavior was revealed. The heating rate and processing melt temperature during the first thermal cycle exhibited a synergistic effect on the SN behavior. Under appropriate conditions, both the first and second thermal cycles can generate SN behavior, but the mechanisms were different. During the secondary thermoforming of carbon fiber-reinforced polyphenylene sulfide (CF/PPS) composites, a vital material for the aerospace field, varied thermal parameters profoundly influence the crystallization behavior of the PPS matrix. Notably, PPS exhibits a distinctive self-nucleation (SN) behavior during repeated thermal cycles. This behavior not only affects its crystallization but also impacts the processing and mechanical properties of PPS and CF/PPS composites. In this article, the effects of various parameters on the SN and non-isothermal crystallization behavior of PPS during two thermal cycles were systematically investigated by differential scanning calorimetry. It was found that the SN behavior was not affected by the cooling rate in the second thermal cycle. Furthermore, the lamellar annealing resulting from the heating process in both thermal cycles affected the temperature range for forming the special SN domain, because of the refined lamellar structure, and expelled various defects. Finally, this study indicated that to control the strong melt memory effect in the first thermal cycle, both the heating rate and processing melt temperature need to be controlled simultaneously. This work reveals that through collaborative control of these parameters, the crystalline morphology, crystallization temperature and crystallization rate in two thermal cycles are controlled. Furthermore, it presents a new perspective for controlling the crystallization behavior of the thermoplastic composite matrix during the secondary thermoforming process. [ABSTRACT FROM AUTHOR]

Hypereutectic Al–Si (20 wt.%) alloy parts were fabricated by employing a powder injection moulding (PIM) technique with a developed multi-component binder system composed of high-density polyethylene (35 wt.%), carnauba wax (62 wt.%) and stearic acid (3 wt.%). The feedstocks contained 83 wt.% metal powders. The debinding process was carried out by a combination of solvent extraction and thermal decomposition. The effects of solvent debinding variables such as kind of solvents, debinding temperatures and time, and the bulk surface area to volume ratios on the debinding process were investigated. Thermal debinding and the subsequent sintering process were carried out in a heating sequence under a nitrogen atmosphere. The influences of sintering temperature and sintering time on the mechanical properties and structure were considered. Under the optimal sintering condition, sintering at 550 °C for 3 h, the final sintering parts were free of distortion and exhibited good mechanical properties. Relative sintered density, Brinell hardness, and tensile strength were ~95.5%, 58 HBW and ~154, respectively. [ABSTRACT FROM AUTHOR]

In this work, a dicyclopentadiene monomer/Grubbs 2 catalyst was added to a mixture of epoxy oligomers and methyl nadic anhydride to obtain a poly‐dicyclopentadiene (DCPD) modified epoxy cross‐linked network via sequential curing. The hybrid resin was used as a matrix for preparing carbon fiber composites. The results indicated that the addition of DCPD monomers significantly reduced the viscosity of the epoxy resin. The toughness and heat resistance of the co‐cured resin was improved without significant loss of strength, which was attributed to the high compatibility between epoxy and the modifier polymer. Regarding the composites, the flexural strength of the hybrid resin‐derived composite first increased and then diminished slightly. Meanwhile, the mode‐I interlaminar fracture toughness continued to increase with the increase of PDCPD content compared to the non‐modified composites. Generally, the change trend of the above properties in the composites was consistent with the change trend of the strength and toughness exhibited in the bulk resin with increasing PDCPD contents, while the change extent was inconsistent due to factors such as fiber volume content and interfacial bonding. Highlights: The epoxy/PDCPD hybrid resin system was obtained via sequential curing.The PDCPD as modifier can reduce the viscosity of the epoxy curing system.The toughness and heat resistance of the PDCPD modified epoxy resin was improved.The loss in flexural strength of the hybrid resin system was insignificant.The GIC of the epoxy composites modified with PDCPD improved appreciably. [ABSTRACT FROM AUTHOR]

Nitrile butadiene rubber (NBR) is widely used in the production of oil and fuel‐resistant rubber parts. Poly(p‐phenyleneterephalamide) (PPTA) pulp is used as a reinforcing fabric in NBR composites to improve its mechanical properties despite the weak bonding between NBR and PPTA pulp. In this work, PPTA pulp was modified by interfacial polymerization of dopamine (DOPA). A surface‐adherent poly(dopamine) (PDA) film was formed on the surface of the PPTA pulp, which improved bonding to NBR and mechanical properties of the prepared composites. The surface of the modified PPTA pulp was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy. The results demonstrate that PDA was successfully functionalized on the PPTA pulp and that the surface of the composite was rougher after modification. The effects of treatment conditions on the mechanical properties of NBR/pulp composites were also investigated. The tensile strength markedly improved with treating time of 30 h at a DOPA concentration of 2 g/L. Strong interactions, including hydrogen bonding and adsorption, play an important role in the tensile strength of the material. Our results demonstrate that surface modification by PDA is beneficial for improving the strength of the NBR matrix. POLYM. COMPOS., 40:E476–E483, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The comprehensive properties of a feedstock have a critical influence on the powder injection molding process. Proper feedstock with homogeneous structure, favorable flow characteristic, and moldability is the prerequisite for obtaining a final part with excellent comprehensive properties. The objective of the present work was to develop an optimal feedstock for fabrication of hypereutectic AlSi (20 wt.%) alloy parts by the powder injection molding technique. For this purpose, micron-sized hypereutectic AlSi (20 wt.%) alloy powder was mixed with different amounts of a binder which consisted of 35 wt.% high-density polyethylene, 62 wt.% carnauba wax, and 3 wt.% stearic acid. The binder contents of the feedstocks were in the range from 13 wt.% to 21 wt.%. The influences of binder content, shear rate, and temperature on the rheological behaviors of feedstocks have been investigated via a capillary rheometer. The feedstock with 21 wt.% binder exhibited a variable flow behavior and was culled. The rest of the feedstocks showed a pseudoplastic behavior. Comprehensive analysis of rheological parameters such as the flow behavior index, yield stress, flow activation energy, and the general moldability index, the feedstock with 17 wt.% binder exhibited the best rheological performance and favorable moldability. The molded part with 17 wt.% binder had constant density, good shape retention, and stiffness as well as homogeneous distribution of the powder and binder. After solvent debinding, the debound item showed a homogeneous porous structure which is suitable for the subsequent thermal debinding and sintering processes. [ABSTRACT FROM AUTHOR]

Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems. [ABSTRACT FROM AUTHOR]

This study addresses the effect of the coatings prepared from aramid nanofibers (ANFs) on the surface treatment of aramid fiber and reinforced polycarbonate (PC) composite (AF/PC). Aramid fiber's smooth, inert surface bonds poorly with polycarbonate. In this research, the PC‐ANF coating was made by the PC/CH2Cl2 solution, which was modified by aramid nanofibers to improve the interfacial adhesion and compatibility of aramid fiber/PC composites. What's more, the silane (KH570) was added to improve the dispersion and interfacial strength of ANF and PC. The results showed the water contact angle of the aramid fiber modified by PSi‐ANF coating was reduced, indicating the modified fiber has a better wettability. The interfacial bonding strength between PC and aramid fiber increased by 77.2%. The AF/PC composites were prepared by hot‐compression, which the aramid fiber wovens treated with P‐ANF coating, PSi‐ANF coating. The tensile strength, flexural strength, interlaminar shear strength, and impact strength of the AF/PC composite reinforced by AF treated with PSi‐ANF containing 2.0 wt% ANF increased by 62.0%, 81.9%, 49.5%, and 27.6%, respectively. Therefore, this study demonstrates that incorporating ANF interphase may offer an innovative and practical way for enhancing the interface bonding properties of aramid‐reinforced composites. [ABSTRACT FROM AUTHOR]

Weak interfacial bonding properties between thermoplastic liners and carbon fiber‐reinforced composites (CFRP) can easily lead to debonding failure, which is a major challenge in development of type IV composite hydrogen storage vessels. We optimized Box–Behnken design atmospheric‐pressure plasma process parameters for maximizing interfacial bonding properties between thermoplastic liner (PA11 liner) and CFRP using Design‐Expert software. From various designs, plasma process parameters, including time (t), nozzle‐to‐specimen distance (d) and gas flow rate (r) of treatment were selected for optimization to assess the effects of their interactions on climbing drum peel (CDP), flatwise tensile (FWT) and asymmetric double cantilever beams (ADCB). The CDP strength, FWT strength and strain energy release rate (GADCB) of untreated samples were 4.2 N·mm/mm, 0.26 MPa and 87.2 J/m2, respectively. After the plasma treatment, optimum process parameters of t = 200 s, d = 12.5 mm, and r = 700 L/h were used to achieve 33.8 N·mm/mm, 2.97 MPa and 1008.4 J/m2, respectively, which were 8.0, 11.4 and 11.6 times that of untreated PA11 surface, respectively. This method has the potential for guiding thermoplastic liner surface treatment of type IV hydrogen storage vessels before winding. [ABSTRACT FROM AUTHOR]

A reliable and optimized process to grow carbon nanotubes (CNTs) in templated pores of polymer derived ceramic (PDC) matrix was developed. It is realized through the pyrolysis of a preceramic polymer, i.e., poly (methyl-phenyl-silsesquioxane) (denoted as PMPS), in argon atmosphere at 1000 °C together with nickel-catalyst-coated poly-methyl-methacrylate (PMMA) microbeads (denoted as PMMA-Ni). PMPS served as both a precursor for the ceramic matrix and a carbon source for the CNT growth. PMMA microbeads were used as sacrificial pore formers and coated with nickel via an electroless plating method, which provides an improved control of particle size of the catalyst and its distribution in the material. The influence of PMMA-Ni loading on the in situ growth of CNTs and the properties of CNTs/SiOC nanocomposites were studied through thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and density/porosity measurements. Under optimized conditions, uniform distribution of in situ grown CNTs was observed within the templated pores of the SiOC matrix. The optimized process leads to reproducible high yield of CNTs in the pores. The development of such novel CNT/cellular ceramic nanocomposite materials is of significant interest for a variety of sensor applications. [ABSTRACT FROM AUTHOR]

Due to their high sensitivity to temperature and humidity, the applications of polylactic acid (PLA) products are limited. The stereo-complexation (SC) formed by poly(L-lactic acid) (PLLA) and its enantiomer poly(D-lactic acid) (PDLA) can effectively improve the heat resistance and hydrolysis resistance of PLA products. In this work, the blended melt-spinning process of PLLA/PDLA was carried out using a polyester fiber production line to obtain PLA fiber with a complete SC structure. The effects of high-temperature tension heat-setting on the crystalline structure, thermal properties, mechanical properties, and hydrolysis resistance were discussed. The results indicated that when the tension heat-setting temperature reached 190 °C, the fiber achieved an almost complete SC structure, and its melting point was 222.5 °C. An accelerated hydrolysis experiment in a 95 °C water bath proved that the SC crystallites had better hydrolysis resistance than homocrystallization (HC). The monofilament strength retention rate of SC−190 fiber reached as high as 78.5% after hydrolysis for 24 h, which was significantly improved compared with PLLA/PDLA drawn fiber. [ABSTRACT FROM AUTHOR]

This study optimized the laminate structure of a composite cylinder under the constraint of minimum layup thickness. Based on the progressive damage theory, a finite element model of the cylinder was established, and the NOL ring tensile test was used to verify the accuracy of the damage theory. The winding angle, the number of layers, and the helical/hoop ratio (the stacking sequence) were selected as the optimization factors, and the burst pressure value was used to evaluate the quality of the laminate structure. Then the orthogonal experiments were designed by RSM. Combined with FEA, the function model of the burst pressure of the gas cylinder and each optimization factor was established to obtain the optimal layering scheme, satisfying the minimum burst pressure. In addition, finite element analysis was used to verify the optimal scheme, demonstrating that the error of the burst pressure predicted by the quadratic model established by the response surface design was not more than 5%. This study provides a faster and more efficient optimization method for the optimization design of composite gas cylinder layers. [ABSTRACT FROM AUTHOR]

Inspired by the application of nano‐fillers in composite materials, well‐dispersed aramid nanofibers (ANFs) were prepared and added into the epoxy resin (EP) to improve the toughness and tenacity properties of the ANF/EP composites. The composites were characterized by mechanical property test, surface analysis, thermodynamic property analysis, and contact angle. Results showed that when the EP was added with 0.15 wt% ANF, the tensile strength, bending strength, and impact strength are increased by 28.2%, 81.9%, and 81.8% compared with pure EP, respectively. The thermal stability and infiltration of the composites are improved. The interlaminar shear strength and interfacial shear strength of the aramid fiber were increased by 53.1% and 92.7% compared with the not reinforced EP, demonstrating that the epoxy reinforced with ANF is also beneficial for improving the interfacial bonding strength of aramid fiber and EP. The mechanism of the epoxy reinforcement by ANF and the interface enhancements showed that the ANF could cause several crack bridges and strong hydrogen bond interaction interface. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical performance of many polymeric materials, such as natural rubber tires, plastic bottles and bags, and textile fibers, depends crucially on the stretch-induced alignment of crystalline molecules in the course of processing. However, the underlying molecular mechanism to solidify the alignment is still poorly understood. We employed dynamic Monte Carlo simulations to unveil how at temperatures close to the melting point a homogeneous stretch of bulk polymers can affect crystal nucleation and leads to aligned crystalline molecules. We observed that upon the molecular strain increasing beyond a critical value, the emerging crystallites suddenly decrease their probability of chain-folding, corresponding to a transition from intramolecular chain-folding nuclei to intermolecular fringed-micelle nuclei. On the basis of the classical nucleation theory, the transition can be predicted well by the competition in the free energy barriers for these two coexisting nucleation mechanisms. [Copyright &y& Elsevier]

Long glass fiber reinforced poly(butylene terephthalate) composites (LGF/PBT) were prepared by a new process. PBT oligomers with low melt viscosity were impregnated into the reinforcing glass fiber and then grafted to the reinforcing glass fiber surface treated with a silane coupling agent during solid‐state polymerization. The reinforcing glass fiber, after removing ungrafted PBT from LGF/PBT, was investigated with the result showing the presence of a grafted PBT layer on the surface of treated glass fiber. The mechanical properties of the composites were significantly improved owing to the grafting of the PBT macromolecules. The fiber length distribution and fiber arrangement in the injection molded composites were also studied and the results showed that a small amount long glass fiber could be connected at junction points in the composites, which were of benefit to the mechanical properties of the composites. [ABSTRACT FROM AUTHOR]

Melt solid polycondensation is an approach to increase the molecular weight of poly (L‐lactic acid) (PLLA). For this report, the effect of crystallization time of PLLA prepolymer on the molecular weight of the biomaterial was studied. In this process, PLLA prepolymer with a molecular weight of 18,000 was first prepared by the ordinary melt‐polycondensation process. The prepolymer was crystallized at 105°C for various times, and then heated at 135°C for 15–50 h for further solid state polycondensation (SSP). The differential scanning calorimetry (DSC) and viscosity measurements were used to characterize the crystalline properties and molecular weight of the resulting PLLA polymers, respectively. The results showed that the molecular weight of PLLA reached a maximum value under the condition of a crystallization time of 30 min and SSP of 35 h. [ABSTRACT FROM AUTHOR]

Abstract: Although poly(l-lactic acid) (PLLA) can be greatly toughened by copolymerization, its lower melting temperature and lower ability of crystallization limit its widespread application as commodity. In order to improve the melting point and ability of crystallization of PLLA based multiblock copolymers, Poly (d-lactic acid) (PDLA) oligomer was used to complex with PLLA–bisphenol A epoxy resin multiblock copolymer (PLLA-co-bis A) to form a stereocomplex. Differential scanning calorimeter (DSC), X-ray diffraction (XRD) and polarized optical microscopy (POM) were used to characterize the thermal properties and crystallization behavior of the stereocomplexes. The results indicated that the stereocomplex of PLLA-co-bis A and PDLA was formed. The formed stereocomplexes with good thermal properties (high T m) and good crystallization properties (high crystallization rate and more stable crystals) are convinced to have high potential as high performance biodegradable polymers. [Copyright &y& Elsevier]

The melt blending of polylactic acid (PLA) and thermoplastic silicone polyurethane (TPSiU) elastomer was performed to toughen PLA. The molecular structure, crystallization, thermal properties, compatibility, mechanical properties and rheological properties of the PLA/TPSiU blends of different mass ratios (100/0, 95/5, 90/10, 85/15 and 80/20) were investigated. The results showed that TPSiU was effectively blended into PLA, but no chemical reaction occurred. The addition of TPSiU had no obvious effect on the glass transition temperature and melting temperature of PLA, but slightly reduced the crystallinity of PLA. The morphology and dynamic mechanical analysis results demonstrated the poor thermodynamic compatibility between PLA and TPSiU. Rheological behavior studies showed that PLA/TPSiU melt was typically pseudoplastic fluid. As the content of TPSiU increased, the apparent viscosity of PLA/TPSiU blends showed a trend of rising first and then falling. The addition of TPSiU had a significant effect on the mechanical properties of PLA/TPSiU blends. When the content of TPSiU was 15 wt%, the elongation at break of the PLA/TPSiU blend reached 22.3% (5.0 times that of pure PLA), and the impact strength reached 19.3 kJ/m2 (4.9 times that of pure PLA), suggesting the favorable toughening effect. [ABSTRACT FROM AUTHOR]

Poor dispersion is a major disadvantage of aramid pulp (AP) reinforced composites. In this study, nano‐silica (SiO2), as the surface modifier and reinforcing agent, was synthesized on AP surfaces to improve the dispersed character in ethylene‐propylene‐diene elastomer (EPDM) using supercritical carbon dioxide (scCO2). The influence of the temperature of scCO2 on treated AP, configuration of the surface, and mechanical performance of AP/EPDM composites were studied. Based on the results of Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy, SiO2 was chemically grafted onto the AP surface. The SiO2 nanoparticles were uniformly deposited on the AP surface, and the roughness of AP was increased based on the SEM results. The optimum temperature of the supercritical reaction was 100°C considering the results of all the tests. Under the optimum temperature and with 10 phr of AP, the mechanical properties, oil resistance, and dynamic mechanical properties of the SiO2‐AP/EPDM composites were investigated. The tensile strength and tear strength of the SiO2‐AP/EPDM were improved by 121.1 and 134.9%, respectively, compared with that of the pure AP/EPDM composites. The fracture surface of the SiO2‐AP/EPDM composites showed that SiO2‐modified AP had a good dispersion in EPDM, and AP and EPDM had good interfacial bonding. Dynamic mechanical analysis results showed that the storage modulus of the composites was improved greatly compared with the pure AP/EPDM, and the loss factor also increased. The oil resistance of the composites was also improved. [ABSTRACT FROM AUTHOR]

The properties of Kevlar fiber‐reinforced composites strongly depend on the dispersion homogeneity of the fiber in matrix and their adhesion. Dispersing fibers into a rubber is more challenging than using traditional fillers, especially for aramid pulp (AP) with a highly branched structure. Herein, we reported a facile pre‐dispersion method to disperse AP in rubber and to enable efficient reinforcement. AP was firstly modified using dopamine to enhance the surface characteristics, and then the modified AP was dispersed in a solution of nitrile‐butadiene rubber (NBR) in ethanol, followed by drying to obtain the AP pre‐dispersion. This pre‐dispersion was incorporated into NBR by a traditional rubber processing method to produce composites. The measurements of Fourier transform infrared, optical and electric microscopies, X‐ray photoelectron spectroscopy, and dynamic mechanical analysis on the composites demonstrate that surface modification using dopamine and the pre‐dispersion method obviously improved the AP dispersabiligy and the interfacial interaction between the pulp and NBR, resulting in the enhanced mechanical and oil‐resistance properties of the composites. [ABSTRACT FROM AUTHOR]

Poor interfacial bonding between stainless steel wire and the inner and outer layer resin matrix significantly affects the mechanical performance of braid-reinforced composite hollow fiber tube, especially torsion control. In this work, a coating of thermoplastic polyurethane (TPU) deposited on the surface of stainless steel wire greatly enhanced the mechanical performance of braid-reinforced composite hollow fiber tube. This method takes advantage of the hydrogen bonding between polyether block amide (PEBA) and thermoplastic polyurethane (TPU) for surface modification of stainless steel wire, as well as the good compatibility between PEBA and TPU. The mechanical properties of composited tubes demonstrate that the interlaminar shear strength, modulus of elasticity, and torque transmission properties were enhanced by 27.8%, 42.1%, and 41.4%, respectively. The results indicating that the interfacial adhesion between the coated stainless steel wire and the inner and outer matrix was improved. In addition, the interfacial properties of composite hollow fiber tube before and after coating was characterized by the optical microscope, and results show that the interfacial adhesion properties of the modified stainless steel wire reinforced resin matrix composites were greatly improved. [ABSTRACT FROM AUTHOR]

Aramid pulp (AP) is a highly fibrillated form of fiber， with excellent heat resistance, wear resistance, size stability, and other beneficial properties, that can be dispersed in rubber or resin matrix systems. Its fibrillation results in a large surface area. However, AP easily tangles and aggregates between fibers because of its large surface area. Consequently, it experiences difficulty in dispersing in matrices, especially when a relatively large amount of pulp is needed to be mixed. In this study, a SiO2 nanoparticle was synthesized on the surface of AP through the hydrolysis of tetraethyl orthosilicate to improve the dispersion of AP in an epoxy matrix. Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, X‐ray photoelectron spectroscopy, and scanning electron microscopy showed that SiO2 nanoparticles coated on the pulp could improve the thermal and mechanical properties. The optimum treatment concentration was 0.15 mol/L. Dynamic mechanical analysis tests indicated when AP modified by SiO2, the E' is higher due to the uniformly diffusion and enhanced interfacial adhesion for load transfer from the epoxy to AP. But Tg is lower as the flexibility chain SiOSi in epoxy. In comparison with the properties of the unmodified AP, the tensile strength and modulus of modified pulp/epoxy composites increased by 53.5% and 160.4%, respectively. Therefore, the dispersion and interface combination of AP modified by SiO2 in the epoxy improved because of the interaction of AP with SiO2 through the hydrogen bonding and crosslinking of SiO2 with epoxy. [ABSTRACT FROM AUTHOR]

A novel polymeric precursor polyborosilazane (PBSZ) for SiBN ternary ceramic fibers was successfully synthesized from trichlorosilane (HSiCl 3), boron trichloride (BCl 3) and hexamethyldisilazane (HDMZ) by a simple one step reaction process. The chemical structures and ceramic yield of the PBSZ precursors were investigated by NMR spectroscopy, FT-IR and TGA. The preparation of PBSZ fibers was conducted in a lab-scale melt-spinning equipment at a spinning speed of 130 m/min. SiBN ternary ceramic fibers were obtained after the non-fusible treatment and pyrolysis of PBSZ fibers in an NH 3 atmosphere. The pyrolysis mechanism, high-temperature behavior and morphologies of the SiBN ternary ceramic fibers were investigated by NMR, XRD, TEM and SEM. The obtained SiBN ternary ceramic fibers had good flexibility, and possessed a tensile strength of 0.84 GPa with a diameter of ∼18 μm. Furthermore, these SiBN ceramic fibers exhibited excellent thermal stability, and maintained the amorphous state up to 1600 °C. [ABSTRACT FROM AUTHOR]

Due to the extraordinary thermal stability, chemical resistance and processability, carbon fiber (CF) reinforced polyetheretherketone (PEEK) composites are widely applied in aviation, aerospace, medical fields, etc. However, the non-polar nature and low wettability of CFs limited the interfacial bonding between CFs and PEEK and results in unsatisfied mechanical properties for CF/PEEK composites. In order to enhance interactions between fibers and matrix, the interface in CF/PEEK composites was built through coating a mixture of polyetherimide (PEI) and functionalized multi-walled carbon nanotubes (COOH-MWCNTs) on CFs. The combination of hydrogen bonding between COOH-MWCNT and PEI as well as the π-π interaction between PEI and PEEK significantly improved the miscibility and interfacial interlocking. As a result, the flexural strength, modulus and interlaminar shear strength (ILSS) of modified CF/PEEK were remarkably improved by 76% (667.8 MPa), 119% (40.0 GPa), and 85% (90.7 MPa) respectively. The failure mechanism changed from smooth cracking in interface destruction to zigzag cracking and resin breakage, suggesting that the resultant interface became strong enough to ensure efficient stress transfer from PEEK to CF. The synergistic interfacial interactions via hydrogen bonding and pi-pi stacking are believed to supply an effective strategy for building high-performance thermoplastic composites. Image 1 • A synergistic interface combined with PEI and COOH-MWCNT is built for improved interfacial adhesion of CF/PEEK composites. • The combination of hydrogen bonding between COOH-MWCNT and PEI as well as the π-π interaction between PEI and PEEK improved interfacial interlocking significantly. • This synergistic interfacial interactions are believed to supply an effective strategy for building high-performance thermoplastic composites. [ABSTRACT FROM AUTHOR]

• Integrated molding the web-reinforced foam sandwich composite lifting lug based on thermal expansion molding process technology. • The influence of the web structure on the compression performance and failure mode of the lifting lug samples is analyzed. • Establish the connection scheme of the steel sleeve and clarify the failure mechanism of the steel sleeve under axial compression. • The connection failure model of the lifting lug is established, and the connection performance and failure mode of the steel sleeve are analyzed by the finite element method and test. • The integrated molding of the battery box verifies the engineering value of TEMP technology. Complex lifting lug connection structures often hinder the integral molding of main load-bearing components in automotive, aerospace, construction, and other fields, thus limiting the potential for lightweight structural design. In this paper, a method of forming web-reinforced sandwich composite lifting lug structure of the new energy vehicle by thermal expansion molding process (TEMP) is proposed, and connection failure analysis model is established to verify the process-structure-performance relationship. First, compression tests and failure analysis confirmed that the web-reinforced structure significantly improved the strength and stiffness of the lifting lugs. Then, the hybrid connection mode of the steel sleeve through the thermal expansion film and glass fiber reinforced plastics (GFRP) was designed, and the reliability of the steel sleeve interface connection was verified by the axial press out test. Finally, the lifting lug was simulated to be mounted on the vehicle body, and the comprehensive connection performance was verified by connection compression test, finite element analysis (FEA) and macroscopic failure mode. This study determined that the web-reinforced structure increased the initial failure load of the lifting lug by 65%, surpassing 60 kN compared to the pure foam sandwich structure. The maximum pressure load of the steel sleeve reaches 11.24 kN, and the comprehensive connection strength can meet the static load of the battery box more than 6000 kg. The TEMP technology has the potential to integrate and scale up main bearing components with complex web reinforcement structures. [ABSTRACT FROM AUTHOR]

High modulus aramid fiber, such as Kevlar 49, is conventionally prepared by the heat annealing of high strength aramid fiber under a suitable tension at high temperature, especially higher than 500 °C. This enables the mobility of a rigid molecule chain to be rearranged into a more perfect crystalline or orientation structure under tension. However, annealing decreases the tensile strength, since the thermal degradation of the molecular chain at high temperature cannot be avoided. Kevlar 49 fibers treated in supercritical carbon dioxide (scCO2) under tension could improve their mechanical properties at a low temperature. The effects of the tension on the mechanical properties and structure of the Kevlar 49 fibers were studied by mechanical testing, wide-angle and small-angle X-ray scattering (WAXS, SAXS), and scanning electron microscopy (SEM). The results show that the mechanical properties, crystallinity and orientation of the fiber can be improved when the tension is less than 0.6 cN/dtex, which may be due to the increasing of the mobility of a rigid segment with the help of the plasticization of scCO2 and re-arrangement of macromolecular chain into crystalline and orientation structure under tension. What's more, the amorphous region also was enhanced by crosslinking reaction of toluene 2,4-diisocyanate (TDI) with the chain end groups of the macromolecules in the amorphous regions. However, a decrease of tenacity was found when the tension was higher than 0.6 cN/dtex, which is because the tension was so high that the microfibril was broken. The results indicated that treating the Kevlar 49 fiber in scCO2 under a suitable tension with TDI as a crosslink agent can simultaneously improve both the tenacity and modulus of the fiber. [ABSTRACT FROM AUTHOR]

Abstract A good understanding of the piezoresistive behavior of carbon fiber is highly valuable in studying the processing-structure-property relationship of this very important engineering material. Up-to-date, there is still a lack of agreement on the physical origin of the unique modulus-dependent piezoresistivity for carbon fibers. In the present work, an experimental and theoretical modeling combined approach was taken to attack this long outstanding issue. A cantilever testing method was developed which allows for the evaluation of the piezoresistive behavior of a single carbon fiber filament under axial tension and compression mode. It was found that the tensile and compressive piezoresistive behavior showed antisymmetric characteristics. This supports the concept that the orientation of the basic structural units (BSUs) is responsible for the piezoresistivity of carbon fibers. Such an argument was further augmented by theoretical modeling of the carbon fiber piezoresistivity based on a Maxwell Garnett theory approach. The new piezoresistivity model identifies the critical role of the compound effect of the BSU orientation and its volume fraction in dictating the piezoresistive behavior of carbon fibers. With consideration of this compound effect, the modulus-dependent piezoresistivity data of carbon fibers reported in the past few decades can now be well explained. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Nano silicon carbide was used separately and as an auxiliary absorber for the modification of the PAN precursor fibers to upgrade their microwave absorbability in order to undergo the subsequent pre-oxidization by using microwave. Surface coatings were successfully applied to the PAN precursor and the coated fibers were pre-oxidized over the microwave furnace for 60 min. To study the effect of the coatings on the pre-oxidized fibers, a series of characterizations were carried out. FTIR analysis results showed clear changes in the basic chemical structure of pre-oxidized fibers, which approved the occurrence of the cyclization and crosslinking reactions. Furthermore, the cyclization was confirmed by the thermal analysis results. According to the listed oxygen values, it can be suggested that the pre-oxidized fibers can resist the high temperatures in the following stage (carbonization). In addition, the crystalline analysis revealed a reduction in crystallinity, while the mechanical analysis demonstrated a reduction in tensile strength and elongation at break of pre-oxidized fibers. Highlights • Single and hybrid coating were applied on PAN fibers. • Coated fibers were used as precursors for the microwave pre-oxidation process. • The pre-oxidation led to polymer decrystallization, cyclization and cross linking reaction. • The polymer crosslinking induced the rearrangement of layer plane cause change of the microstructure parameters. • More developed conjugated structure was obtained in pre-oxidized hybrid fibers. [ABSTRACT FROM AUTHOR]

Polyborosilazane synthesized from trichlorosilane (SiHCl 3 ), boron trichloride (BCl 3 ) and methylamine (MeNH 2 ) is highly sensitive to moisture for hydrolysis of -NHMe unites and is easy to cross-link for dehydrogenation of Si-H, N-H, which affected the industrial scale production of SiBNC ceramic fibers. In this paper,a new nitrogen source(n-propylamine, C 3 H 7 NH 2 ) was used instead of MeNH 2 to synthesis polyborosilazane precursor. The influences of nitrogen sources on the structures and properties of SiBNC ceramic fiber precursors were investigated. As compared to SiHCl 3 /BCl 3 /CH 3 NH 2 system, polyborosilazane precursor synthesized from the SiHCl 3 /BCl 3 /C 3 H 7 NH 2 system exhibited lower crosslink density, lower sensitivity to moisture and good melt spinnability, and the obtained ceramic fibers showed higher tensile strength (1.03 GPa, an increase of about 37.3%). This synthesis route (SiHCl 3 /BCl 3 /C 3 H 7 NH 2 ) may serve as a suitable synthetic route for a large-scale production of SiBNC ceramic fibers. [ABSTRACT FROM AUTHOR]

In this paper, hydroxyl terminated polyethersulfone(PES) was used as a toughening agent to modify the monocomponent high performance epoxy resin by blending. The solubility of PES in epoxy resin and the curing performance, mechanical properties, morphology, viscoelastic properties and thermal properties of epoxy/PES blends were investigated, respectively. The dissolution experiment results showed that the hydroxyl terminated PES had a good compatibility with the epoxy resin and could be dissolved in epoxy resin under controlled conditions. FT-IR studies showed that the addition of PES did not affect the result of epoxy resin curing reaction. The results of the mechanical properties of the epoxy/PES blends indicated a 32% and 9% enhancement in fracture toughness and impact strength respectively, which can be ascribed to the bicontinuous phase structure of the epoxy/PES blends. Reaction induced phase separation was observed in the epoxy/PES blends during the curing process of epoxy resin, which presented dispersed particles, bicontinuous and phase inverted structures with the increase of the PES content. Thermogravimetric analysis revealed that the thermal stability of the epoxy/PES blends were slightly increased compared to that of the pure epoxy resin. Thus, the hydroxyl terminated PES could be used to improve the mechanical and thermal properties of the monocomponent high performance epoxy resin. [ABSTRACT FROM AUTHOR]

Polyphenylene sulfide (PPS), as a typical resin for aerospace thermoplastic composites, often undergoes repeated melting and crystallization during thermoforming. Thermal histories can introduce the self-nucleation (SN) effect in certain circumstances, which will significantly accelerate the overall crystallization rate of PPS. In this article, the SN behavior of PPS and its influence on nonisothermal and isothermal crystallization behavior were studied by differential scanning calorimetry, and the multiscale crystalline morphology and structure were characterized. A unique SN domain within the temperature range of 292 °C–323 °C was identified, where the melting endotherm reaches the melt baseline and the peak crystallization temperature remains stable, while the spherulite size is several hundred nanometers. The mechanisms of the impact of molecular chain topology at different melting temperatures on the SN behavior were proposed. This work provides guidance for the design of PPS crystalline structure and suggests a stable thermoforming processing region, approximately 20 °C above the melting point. Schematic diagram of strong memory effect of PPS Domain II' and molecular chain conformation in the melt. [Display omitted] • With the self-nucleation effect in the crystallization of PPS, a stable thermal processing region can be built. • Crystalline morphologies of PPS can be modulated by self-nucleation effect. • Mechanisms of the impact of molecular chain topology at different melting temperatures on SN behavior were proposed. [ABSTRACT FROM AUTHOR]

In this paper, polyborosilazane precursor was synthesied from HMDZ, HSiCl 3 , BCl 3 and CH 3 NH 2 using a multistep method. By controlling the storage conditions, parts of the polyborosilazane fibers were hydrolyzed. FT-IR, NMR, XRD, TEM and monofilament tensile strength test were employed to study the effects of hydrolysis of precursor on the structures and properties of polymer-derived SiBN ceramic fibers. FT-IR and NMR results indicate that Si-N group in PBSZ reacts with H 2 O to form Si-O-Si group. After pyrolysis reaction at 1400℃, Si-O-Si group will finally transformed into highly ordered cristobalite and β-quartz, resulting in formation of the wrinkled surface of the obtained SiBN ceramic fiber. The strip-like defects on fiber surface, according to monofilament tensile strength test, had a significant effect on mechanical property of the obtained SiBN ceramic fiber and caused no increase in fiber tensile strength of hydrolytic polyborosilazane fiber before and after pyrolytic process. [ABSTRACT FROM AUTHOR]

In order to prepare Polyethersulfone (PES) melt-spun fibers, epoxy (EP) oligomer was adopted as a novel plasticizer. The plasticization of EP on PES was investigated by differential scanning calorimetry (DSC), fourier transform infrared (FTIR), and rheological techniques. The results revealed that the glass transition temperature ( T g ), the complex viscosity ( η ∗ ), and melt processing temperature ( T mp ) of PES/EP blends decreased significantly with the increase of EP content. FTIR spectroscopy and rheological behavior demonstrated no signs of crosslinking reactions occurring between PES and EP molecules. Finally, PES melt-spun fibers were successfully obtained by using EP as a plasticizer, showing the highest tensile strength at 2.71 cN/dtex. The morphologies of the fibers observed by scanning electron microscopy (SEM) presented smooth and uniform surface, and compact fracture. [ABSTRACT FROM AUTHOR]

A novel processable and high yield polyborosilazane (PBSZ) precursor for SiBNC ceramic fibers was synthesized via boron trichloride (BCl 3 ), co-polymerization of trichlorosilane (SiHCl 3 ) and methylamine (MeNH 2 ), followed by trans-amination with NH 3 . The synthesized PBSZ precursor was characterized and the results showed that the polymeric precursor exhibited good melt–processability and green fibers with a diameter of 45 µm could be easily obtained by melt spinning. The green fibers were subsequently pyrolyzed at 1200 °C in nitrogen atmospheres to provide SiBNC ceramic fibers with a cylindrical hollow structure, ca.32 µm in diameter and 720 MPa in tensile strength. The green fibers had an approximately ceramic yield of 78% at 900 °C. [ABSTRACT FROM AUTHOR]

In this paper, polymer precursor polyborosilazane (PBSZ) was synthesized from hexamethyldisilazane, HSiCl 3 , BCl 3 and CH 3 NH 2 using a multi-step polymerization process. Continuous PBSZ fibers were prepared by a laboratory scale melt-spinning machine. SiBN ceramic fibers were then obtained by the pyrolysis of PBSZ fibers. The chemical structure character and its ceramic conversion of the polymer precursor were presented. After high temperature pyrolysis process at 1100 °C, SiBN ceramic fibers were obtained with a diameter of about 14 μm. Those fibers showed average tensile strength of 0.87 GPa. The carbon content of the obtained SiBN ceramic fibers was less than 0.1 wt%. SiBN ceramic fibers revealed excellent dielectric properties and structural stability at high temperatures. [ABSTRACT FROM AUTHOR]

Zirconium diboride (ZrB 2 ) films were produced by liquid hybrid precursor method. Firstly, solutions of zirconium oxychloride octahydrate (ZrOCl 2 ·8H 2 O), boric acid, sucrose and citric acid were mixed. Secondly, ammonium hydroxide was utilized to adjust pH and polyvinyl alcohol (PVA) acted as the aid of film formation. Next, through dip-coating and multi-step drying method, ZrB 2 precursor films were fabricated. Finally, ZrB 2 ceramic films were obtained via pyrolyzing the hybrid precursor at high temperature. The pyrolysis behaviors of the precursor were also investigated by XRD, SEM and pore-size distribution analysis. It was found that relatively stable structure was produced by sol-gel among the raw materials. The densification of ceramic films was reinforced as the pyrolysis temperature increased. As a result, the ZrB 2 ceramic film obtained at 1600 °C exhibited integrated crystal structure and uniform morphology with pores diameter of 2–5 nm. [ABSTRACT FROM AUTHOR]

• The TiO 2 nanoparticles are formed on the pre-oxidized PAN nanofibers in ScCO 2. • Activation heat treatment improves the adsorption and photocatalysis of fibers. • TiO 2 /ACNF has the best degradation effect on methyl orange solution. Polyacrylonitrile (PAN)-based activated carbon nanofibers were used as a photocatalyst carrier and framework due to its large specific area and can adsorb organic pollutants. In this paper, the supercritical carbon dioxide was used to deposit TiO 2 on the surface of pre-oxidized PAN nanofibers, and the fibers were activated by heat treatment to prepare activated carbon nanofibers-TiO 2 (TiO 2 /ACNF). The morphology, structure and specific surface area of the modified nanofibers were analyzed, and the degradation test of methyl orange was carried out. The results showed that TiO 2 nanoparticles can be uniformly loaded on the surface of pre-oxidized PAN nanofibers after supercritical treatment. The specific surface area of the TiO 2 /ACNF after activated heat treatment can reach 422.8 m2/g, having higher adsorption and photocatalytic degradation performance. [ABSTRACT FROM AUTHOR]

The high-ortho epoxy phenolic fibers (HEPFs) were prepared by the crosslinking of as-spun filaments derived from melt-spinning of the epoxy novolac resins copolymerized among epichlorohydrin (ECH), phenol and formaldehyde, and cured in a combined solution of formaldehyde and hydrochloric acid with a different heating rate. The changes in functional groups, thermal performance and mechanical properties during the different heating rates in solution curing were characterized. The results show that a peak of thermal stability and mechanical properties can be obtained with increasing heating rate, and crosslinking structure and characteristic group have changed after the solution curing. The epoxy phenolic fibers show great potential in the application of elastic flame-resistant textiles, aero-composites and precursors for activated carbon fibers used in electronic devices. [ABSTRACT FROM AUTHOR]

The kinetics of stepwise polymerization in the diffusion-controlled regime was investigated using dynamic Monte Carlo simulation and scaling analysis. In analogy to Flory’s expression, a concise expression of reaction kinetics in diffusion controlled regime was proposed, where the number average degree of polymerization was related to the initial concentration and reaction time through a power law dependence. In addition, the transition of kinetics from the classical reaction-controlled to diffusion-controlled regime was predicted and examined via simulation. The results provided a good description of kinetics for the late stage of stepwise polymerizations, and demonstrated good agreements with the various experiments. [ABSTRACT FROM AUTHOR]

In this work, the tackified PDCPD (PDCPD-T) specialized for vacuum assistant resin infusion process (VARI) was developed. The epoxy resin and methyl nadic anhydride (NMA) was subsequently added to the PDCPD-T to improve the interfacial bonding with the carbon fibres. The results showed that the introduction of NMA-cured epoxy undermined the mechanical properties of the PDCPD-T owing to the agglomeration of the tackifier particles. Nonetheless, the mechanical properties of the CFRCs based on the co-cured blends of the PDCPD-T and the NMA-cured epoxy were comprehensively improved compared to the composites based on the PDCPD-T. The improvement was that a part of NMA-cured epoxy in the co-cured blends would phase separate on the surface of the carbon fibre, which formed the "bridge" connecting the matrix and the carbon fibre. In addition, the degree of the tackifier agglomeration would also decrease due to the decrease in the surrounding epoxy concentration. [Display omitted] • The continuous carbon fiber reinforced polydicyclopentadiene (PDCPD) composites based on the vacuum-assisted resin infusion process are realized by tackifying the dicyclopentadiene (DCPD) monomer. • The further addition of anhydride-cured epoxy resin to the tackified DCPD monomer solves the problem of poor interfacial bonding between the PDCPD resin and the carbon fiber. • The carbon fiber composites based on the modified PDCPD matrix are proved to be far superior in interlaminar fracture toughness and impact resistance than the epoxy-based composites. [ABSTRACT FROM AUTHOR]

Web-reinforced foam sandwich structures have excellent mechanical properties due to the enhancement of the structural moment of inertia and the increase in the degree of integration. The present study prepared foam sandwich composites and web-reinforced foam sandwich composites through a novel thermal expansion molding process (TEMP). In addition, four conventional structures, including laminate, foam sandwich, I-beam composite, and web-reinforced foam sandwich structures, were prepared using vacuum-bag-only (VBO) technology. The feasibility of the technology was explored through the structure and properties of foam, the matching of foam and resin, and the porosity of the composites after forming. The three-point bending test showed that the stiffness and strength of the web reinforced foam sandwich prepared by TEMP technology are increased by 18.8% and 4.1%, respectively, compared with VBO technology. Moreover, the TEMP technology was more effective in processing the sandwich composite compared with the VBO technology. The failure mechanisms of the web-reinforced foam sandwich composite for the three-point bending experiment were determined by finite element analysis (FEA), and the accuracy of the finite element model was verified. The TEMP technology involved in this research provides guidance for the application of complex web-reinforced foam sandwich composites in the field of lightweight. [ABSTRACT FROM AUTHOR]

A novel precursor for preparing SiBNC ceramic fibers was successfully prepared via co-polymerization of trichlorosilane (SiHCl 3 ), boron trichloride (BCl 3 ) and methyl amine (MeNH 2 ). The polymeric precursor exhibited good melt spinnability due to its relatively linear-chain chemical structure, which could be easily melt spun into green fibers with a diameter of 28 μm. The green fibers were subsequently pyrolyzed to SiBNC ceramic fibers with ca. 24 μm in diameter and 750 MPa in tensile strength. The polymer-to-ceramic conversion was investigated by the means of thermogravimetric analysis (TGA) and nuclear magnetic resonance spectroscopy (NMR). [ABSTRACT FROM AUTHOR]

Effects of external tension during oxidative stabilization of melt-spun polyacrylonitrile (PAN) precursor fibers on the structure and properties were investigated. The results showed that the external tension had distinct effects on the chemical and crystal structures, carbon yield, density, and tensile strength of pre-oxidized melt-spun fibers, while had little effects on elemental contents. With external tension increasing, the extent of reaction (EOR), aromatization index (AI), carbon yield, and density of pre-oxidized melt-spun fibers showed an initial increase and then a subsequent decrease, while, crystal size, crystallinity and the tensile strength appeared to first fall and then rise. When the external tension was 0.56 cN · dtex−1, the tensile strength of resulting carbon fibers reached maximum. [ABSTRACT FROM AUTHOR]