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Designing hydrogels with adequate strength, remarkable swelling resistance, low friction coefficient, excellent biocompatibility, and osseointegration potential is essential for replacing articular cartilage. However, it remains challenging to integrate all these properties into one material. In this work, a Janus hydrogel was prepared from polyvinyl alcohol, chitosan, and sodium hyaluronate, followed by a one-sided dipping in situ precipitation mineralization to form a layer of hybridized hydroxyapatite (HAp), wherein the two surfaces had distinct compositions and functions. Because of the negative carboxyl groups from sodium hyaluronate, the top surface possessed a friction coefficient as low as 0.024. On account of the HAp mineralized layer, the bottom side had osteogenesis potential. Owing to the synergy of physical linkages, the hydrogel displayed compressive strength as high as 78 MPa. Furthermore, it demonstrated remarkable swelling resistance with strength retention near 100% even after soaking in PBS solution at 37 °C for 7 days. The absence of toxic chemicals maintained the merits of starting polymers and resulted in excellent biocompatibility (cell viability ≈ 100%), making it an ideal substitute for articular cartilage.

Polarized optical micrographs of PEN/H-ZnOc blends: (a) 0 wt%, (b) 0.4 wt%, (c) 0.6 wt%, (d) 1.0 wt%, (e) 1.5 wt% isothermally crystallized at 200 °C for 40 min.

A very small amount of aryl amide derivative (TMB-5) was used for nucleating Poly(ethylene 2,6-naphathalate) (PEN) by melt blending. The crystalline temperature, crystallinity, and nucleation effic...

Bicyclic [2.2.1] heptane-2,3-dicarboxylic acid disodium salt (HPN-68L) and poly(ethylene 2,6-naphthalate) (PEN) blends were prepared by using a twin-screw extruder. The effects of HPN-68L on the crystallization behavior, intrinsic viscosity and mechanical properties of PEN were systematically investigated. The results showed that HPN-68L shows a significant nucleation effect on PEN. The nucleation efficiency basically increased with the increase of HPN-68L content and reached up the maximum value of 53.27% when the HPN-68L was 0.4%. However, the degree of crystallinity of PEN raised up firstly and then decreased with the increasing of HPN-68 content. So the optimized content of HPN-68L is 0.2 wt% and the crystallization peak temperature of PEN apparently increased by 8.74 °C with the addition of 0.2 wt% HPN-68L during the cooling process. But the corresponding mechanical properties including toughness and elongation-at-break(%) were the worst. The reason were discussed. Additionally, the nucleation mechanism were also proposed.

Different crystal planes of nanocrystalline often displayed diverse physical and chemical properties. In this paper, the effects of nano-ZnO with two kinds of crystal planes on crystallization, thermal stability and mechanical properties of PLLA were investigated. The results show that the (1010) planes with no-polar and low surface energy increased the chain mobility of PLLA chain, showed a plasticizing effect; the glass transition temperature, melt and cold crystallization temperature decreased by 12 °C, 10 °C and 12 °C, respectively. The size of spherulites increased and the number of spherulites decreased, the crystal form changed from mixed crystal form α, α′ to unique α crystal form. However, the (0002) planes with polar and high surface energy has highly nucleating effective for PLLA, the crystallization temperature increased to 106.41 °C, the cold crystallization peak disappear. The size of spherulites decreased and the number of spherulites increased. Moreover, the (0002) planes increases the elongation at break of PLLA to 20.34% but the (1010) planes reduces to 7.49%. Their thermo-gravimetric analysis results showed the similar trend. Our results indicate that the interface wettability and compatibility between crystal planes and PLLA, which was caused by the polarity and surface energy of (1010) or (0002) planes played key role in improving the performance of polymers.

The nanocrystalline with different crystal planes often displayed diverse physical and chemical properties. However, the effects of crystal planes of inorganic nano-particle have been few focused on. Here, two kinds of nano-crystal ZnO with different crystal planes were used to explore their effect on the crystallization nucleation, crystal morphologies, thermal and thermal-oxidation stability of iPP. The results shown that the (1010) and (0002) planes possessed different effects for iPP. The (1010) planes with non-polar and low surface energy has highly nucleating effective for iPP, the crystallization temperature increased by 11 °C, the size of spherulites decreased, the number of spherulites increased, the nucleation efficiency and crystallization rate up to 57.81% and 1.27 min−1, the thermal and thermal oxidation stability (TG, OIT, OOT) of iPP improved by 6 °C, 6 min and 12 °C. In contrast, the (0002) planes with polar and high surface energy have no effect for iPP. Our research results indicate that the wettability and interface compatibility between crystal planes and iPP matrix, which was caused by the polarity and surface energy of (1010) or (0002) planes played key role in improving the performance of polymers.

In view of the low crystallization rate of poly(ethylene 2,6-naphthalate) (PEN), in order to elevate its crystallization rate, a phenylphosphonic acid salts compound (TMC-210) with efficient nucleation ability was acted as nucleating substance in this study. Therefore, the PEN/TMC-210 blends were prepared by melt blending. The variation of crystallization peak temperature, nucleation efficiency, and density of crystal nucleus reflect the improvement of PEN crystallization rate, and conduct an in-depth model analysis of non-isothermal and isothermal crystallization. Although the crystal structure of PEN has not been changed, the PEN/TMC-210 blends appeared new diffraction peaks in x-ray diffraction spectrogram, which may attribute to the agglomeration of TMC-210 particles. The new stress-whitening on the impact fracture surface of the PEN/TMC-210 blends confirm the enhancement of PEN tenacity.

Fabricating robust and multi-functional hydrogels is of great importance and challenge. In this work, chitosan (CS) and polyvinyl alcohol (PVA) were used to design antiseptic, conductive and robust hydrogels by a two-step method. Chemical structures of gels, the degree of crystallinity, the state of water in hydrogels, as well as their microstructures were characterized via a combination of FT-IR, XRD, DSC and SEM. Segment lengths of cross-linking points were calculated from elastic rubber theory. Their mechanical properties were evaluated on the electronic testing machine. It was shown that the tensile strength and elongation at break of single PVA hydrogel were only 200 kPa and 135%, respectively, due to the heterogenous structure with pore sizes between 1.5 ~ 8.2 μm. By introducing CS into PVA matrix followed with soaking in a saturated NaCl solution, the network became homogeneous with a pore size of 0.5 ~ 1.1 μm. Moreover, free water changed to bond water, and frictions between polymer chains increased because of hydrophobic associations and entanglements of CS segments. As a result, the tensile stress and strain increased to 3800 kPa and 270%, respectively. The gel also exhibited antiseptic property, electrical conductivity and swelling-resistant properties. The strength after reaching swell equilibrium was 3400 kPa, much higher than most gels at swollen states. This gel might find applications in bionic cartilage, sensors, food preservation and wearable devices.

Nanocellulose (NC) possesses low density, high aspect ratio, impressive mechanical properties, nanoscale dimensions, which shows huge potential applications as a reinforced filler. Polyolefin (PO), represented by polyethylene (PE) and polypropylene (PP), has been widely used in industries. Recently nanocellulose/polyolefin nanocomposites (NC/PO nanocomposites) have caught more attention from the application of automotive components, aerospace, furniture, building, home appliances, and sport. In this review, the surface modifications of nanocellulose and polyolefin are summarized respectively, such as surface adsorption modification, small molecule modification, and graft copolymerization modification. The common preparations of NC/PO nanocomposites are discussed, including the melting compounding, the solvent casting, and the in-situ polymerization. The lightweight, mechanical properties, and aging-resistant properties of NC/PO nanocomposites are highlighted. Finally, the potentials and challenges for industrial production development of NC/PO nanocomposites are discussed.

For filler-polymer systems, the ultimate importance of interfacial interactions between fillers and polymers lies in improving morphological developments and properties of composites. In this work, sepiolite fiber (SEP)/polyoxymethylene (POM) is formulated through melt extrusion processing, with the aim of promoting the crystallization and overall performance of POM. Results show that hydrogen bonding prevails between SEP hydroxyls and POM C-O-C groups. Thus SEP fibers are dispersed uniformly in the POM matrix due to interfacial interactions between these two components. During the isothermal crystallization process, POM nuclei originate and grow on the SEP surface, resulting in decreasing spherulite sizes and facilitating the POM crystallization. Meanwhile, the crystallinity of POM is increased from 48.3% to 54.1% by the addition of 5 wt% SEP. Noteworthily, mechanical and thermostability performances of SEP/POM composites have been improved considerably by means of sufficient interfacial interactions, enhanced crystallization, and favorable physical properties of SEP. Maximum values of the tensile strength and modulus at 3.0 wt% SEP loading can reach 66 MPa and 2022 MPa, respectively higher than those of neat POM.

To resolve the problems of phase separation in the process of toughness improvement for poly (ethylene terephthalate) (PET) by blending rubber phase, referencing the technology of interpenetrating polymer network (IPN) hindering phase separation, here a solution of phase separation restraining was developed in the process of adding thermoplastic polyester-ether elastomer (TPEE) to improve the toughness of PET by using nucleation agent bicyclo[2.2.1]heptane-2,3-dicarboxylic acid disodium salt (HPN-68 L) to enhance greatly gelation temperature to hinder the melt movement under the high temperature. It was found that TPEE and HPN-68 L could improve the crystallization rate and toughness of PET at the same time. The long period of PET increased after adding HPN-68 L and TPEE, while the crystal form of PET had a negligible effect. In addition, the spherulites arranged more closely and the size was more uniform after adding the nucleator HPN-68 L into PET/TPEE blends. In mechanical properties testing, with increasing the TPEE content, the flexural strength and flexural modulus of PET/TPEE/HPN-68 L blends were decreased, but the toughness of the blends was greatly improved. Especially, no distinct phase separation was observed and the tissue morphology of the blends was very uniform.

Chain branching (CB) of Poly(L-lactic acid) (PLLA) can regulate the crystallization. This paper aimed at the disadvantages of time and energy-consuming of CB PLLA which obtained by chemical method, CB PLLA with side chain of 3-Pentadecylphenol (PDP) was prepared with the help of intermolecular hydrogen bonding by simple blend method. Intermolecular force between PLLA and PDP was studied by means of fourier transform infrared (FTIR) spectrometer and nuclear magnetic resonance (NMR). The results show that intermolecular hydrogen bonding forms between carbonyl groups of PLLA and hydroxyl groups of PDP. The non-isothermal crystallization, melting and glass transition behavior of PLLA and CB PLLA were investigated by differential scanning calorimeter (DSC). The results show that CB PLLA display an obvious crystallization peak and the alkyl chain of the PDP occur confined crystallization in PLLA. The melt crystallization temperature (Tc) and glass transition temperature (Tg) of the CB PLLA decrease with the increase of PDP content. Wide angle X-ray diffraction (WAXD) analysis reveal that the addition of PDP does not modify the crystal structure of PLLA, but results in less compact crystal structure. The results obtained by polarized optical microscopy (POM) indicate that the spherulite morphology of PLLA becomes ring-banded spherulite when PDP content reach up to 15 wt%, and the size of the spherulites increase with the increase of PDP content. Thermal gravimetric (TG) analysis show that the thermal stability of CB PLLA decrease with PDP incorporation, but still hold a high decomposition temperature.

A new chain shuttling polymerization system was developed that utilizes only one neodymium precatalyst and two different types of cocatalysts to prepare cis-1,4/trans-1,4 stereo multiblock polybutadienes. This study provides a new alternative to achieve conjugated diene chain shuttling polymerization. For the butadiene polymerization with Nd(Oi-Pr)3/MMAO/Mg(n-Bu)2 system, a gradual reduction of the Mn of the resultant polymer with Mg(n-Bu)2 content increased while retaining narrow molecular weight distributions and unimodal GPC profiles, which indicated the occurrence of fast and reversible chain transfer. The trans-1,4 content increased from 7.7 % to 50.6 % with Mg(n-Bu)2 content increased, Mg(n-Bu)2 both served as cocatalyst to generate trans-1,4 regulating species and as chain transfer agent capable of shuttling the formed polymer chains between the two active species. Furthermore, the number-average degree of polymerization of the trans and cis blocks can be calculated from 13C NMR analysis. Differential scanning calorimetry and dynamic mechanical analysis was also performed to further validate the cis-1,4/trans-1,4 multiblock structure.

The blends of poly (butylene terephthalate) (PBT) and 4,4′-dihydroxyphenyl (DHP) were prepared by melt blending, and the effects of DHP on the crystallization and melting behaviors of PBT were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). The results showed that crystallization temperature and crystallinity of PBT apparently decreased with the addition of DHP. A remarkably decline in crystallization rate of PBT was achieved, and the blends had higher σ e and q values than that of pure PBT as analyzed based on the Avrami equation and Lauritzen-Hoffman equation. The crystal structure of PBT did not change by the addition of DHP, while the spherulite size of PBT decreased.

In order to overcome the low crystallization rate of poly(ethylene terephthalate) (PET), bicyclo[2.2.1]heptane-2,3-dicarboxylic acid disodium salt (HPN-68L), a highly active organic nucleating agent for polypropylene, was selected to replace the special nucleating agent of PET to improve PET crystallization due to its carboxylate anion structure, which usually shows a high induced nucleation ability for PET. The crystallization and properties of the composites were systematically investigated. It was found that HPN-68L had a significant nucleation effect on PET. The crystallization temperature and the nucleation efficiency of PET was increased by approximately 14 °C and 68.4%, respectively at a very low content of 0.6 wt% HPN-68L. Moreover, the half-time of crystallization and isothermal crystallization activation energy decreased upon the addition of HPN-68L. The long period of PET decreased and the number of spherulites increased after adding HPN-68L, while the crystal form of PET did not change. In addition, the nucleation mechanism of HPN-68L induced PET crystallization was studied and a chemical degradation nucleation mechanism was proposed. The flexural strength and modulus of PET were improved, whereas the impact strength decreased to a certain extent upon the addition of HPN-68L.

The poly (butylene succinate-co-butylene adipate) (PBSA)/thiodiphenol (TDP) complexes were prepared by melt blending. Intermolecular hydrogen bonding between carbonyl group of PBSA and hydroxyl group of TDP formed as verified by a combination FTIR and peak fitting technique. As a result, the crystallization temperature, melting temperature, crystallinity and crystallization rate of PBSA decreased with addition of TDP, implying impeded crystallization and reduced lamellar thickness. On the basis of Lauritzen–Hoffman analysis, the fold surface energy (σe) and work of chain folding (q) were increased by TDP incorporation. POM observation exhibited concentric ring-banded spherulites for samples with 10 and 20 wt% TDP. A peculiar ring-banded pattern with discrepant band spacing was obtained for the first time by addition of 30 wt% TDP, whose formation mechanism remains to be discussed. Copyright © 2016 John Wiley & Sons, Ltd.

A styrene derivative, 4-N,N-dimethylaminostyrene (MAS), serving as both catalyst and monomer was exploited in reversible complexation mediated polymerization (RCMP). Radical trap experiment and UV–vis spectroscopy analysis revealed that MAS as a catalyst could abstract iodine from iodine-containing compound to generate propagating radical species. Kinetic studies demonstrated that the polymerization of styrene in the presence of MAS proceeded in a “living”/controlled manner, affording polymers with controlled molecular weights and narrow molecular weight distributions. The livingness of the obtained polymer was confirmed by chain extension. Determined by water contact angle measurement, incorporation of MAS into the polymer led to the enhancement of surface energy. Moreover, using α,ω-bis(2-iodo-2-phenylacetoxy)-end functionalized cis-1,4-polyisoprene as a macroinitiator which was synthesized through cross-metathesis of cis-1,4-polyisoprene with cis-1, 4-bis(2-iodo-2-phenylacetoxy)-2-butene, the polymerization of styrene in the presence of MAS also exhibited typical features of “living”/controlled radical polymerization to yield polystyrene-block-polyisoprene-block-polystyrene.

Lamellar assembly with fractal-patterned growth into dendritic and ringed spherulites of crystallized poly(l-lactic acid) (PLLA), of two molecular weight (MW) grades and crystallized at (temperature of crystallization) Tc = 120 and 130 °C, respectively, are evaluated using optical and atomic-force microscopies. The results of surface-relief patterns in correlation with interior microscopy analyses in this work strongly indicate that the observed birefringence changes in PLLA polymer dendritic or ringed spherulites (from blue to orange, or to optical extinction) need not be definitely associated with the continuous helix twisting of lamellae; they can be caused by sudden and discontinuous lamellae branching at intersected angles with respect to the original main lamellae, as proven in the case of dendritic and zig-zag rough-ringed spherulites. Intersection angles between the main stalks and branches tend to be governed by polymer crystal lattices; for PLLA, the orthorhombic lattice (α-form) usually gives a 60° angle of branching and hexagonal growth. The branching lamellae then further bend to convex or concave shapes and finally make a 60–90° angle with respect to the main stalks. Such mechanisms are proven to exist in the straight dendritic/striped high-molecular weight (HMW)-PLLA spherulites (Tc = 120 °C); similar mechanisms also work in circularly ringed (Tc = 130 °C) HMW-PLLA spherulites.

Intermolecular hydrogen-bonding could be formed between poly(butylene terephthalate) (PBT) and 4,4′-thiodiphenol (TDP) which was verified using advanced quantum-chemistry calculations. Blends of PBT and TDP were prepared through melt blending and the intermolecular hydrogen-bonding was characterized using Fourier transform infrared spectroscopy (FTIR). The results showed that intermolecular hydrogen-bonding formed between the carbonyl group of PBT and hydroxyl group of TDP, the carbonyl and hydroxyl absorption bands shifted to a lower wavenumber and the shape of the hydroxyl peaks became wider asymmetrically with increasing TDP content. The effects of hydrogen bonding on the crystallization and melting behaviors of PBT were investigated using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). The results showed that both the non-isothermal melt-crystallization behavior and isothermal crystallization kinetics of PBT were inhibited by the addition of TDP. The overall isothermal crystallization rates of PBT in the PBT/TDP blends were obviously slower than that of pure PBT at the same crystallization temperature. The crystal structure of PBT did not change through the incorporation of TDP, while the crystallinity and the crystal size of PBT decreased with increasing TDP content.

Poly(ethylene terephthalate) (PET) and aryl amide derivative (TMB-5) blends were prepared by melt blending. It was found that TMB-5 shows a significant nucleation effect on PET and especially the non-isothermal nucleation efficiency reached up to 80.7% at a very low content of 0.6 wt% TMB-5. The effects of TMB-5 on the crystallization behavior and mechanical properties of PET were systematically investigated. DSC results show that crystallization temperature of PET apparently increased by nearly 20 °C with the addition of 0.6 wt% TMB-5 during the cooling process. A remarkable acceleration in the crystallization rate of PET was achieved as analyzed using the Avrami equation. Wide angle X-ray diffraction (WAXD) and polarized optical microscopy (POM) results show that the addition of TMB-5 remarkably increases the crystallinity and nuclei density of PET. Small angle X-ray scattering (SAXS) measurements reveal that the long period of PET decreased and lamellar thickness increased with an increase in TMB-5 content. The impact strength of PET was greatly enhanced by the addition of TMB-5, and a toughening mechanism was proposed.

A low molecular weight hydrazide compound, tetramethylenedicarboxylic di (2-hydroxybenzohydrazide) (TMBH), greatly improves the crystallization rate and crystallinity of poly(l-lactide) (PLLA). The nucleating efficiency of TMBH on the crystallization of PLLA exhibits obvious concentration dependence, which increases first and then decreases slightly with the increase of TMBH loading, reaching a maximum at 0.3 wt%. Time-resolved Fourier transform infrared spectroscopy spectra indicate that the formation of skeletal conformational ordering structure of PLLA has been accelerated in the presence of TMBH, which can act as efficient precursors speeding up both the nucleation of PLLA on TMBH surface and the formation of intrachain 10(3) helix structure. The possible hydrogen bonding interaction between the OH or NH groups in TMBH and the CO groups in PLLA backbones is supposed to be an important factor, which promotes the migration of PLLA chains to TMBH crystallites and the emergence of interchain interactions as well as the conformational ordering.

In this study, we synthesized a new multifunctional benzoxazine monomer Azo-COOH-Py BZ—featuring an azobenzene unit, a carboxylic acid group, and a pyrene moiety—through the reaction of 4-(4-hydroxyphenylazo)benzoic acid (Azo-COOH), paraformaldehyde, and aminopyrene (Py-NH2) in 1,4-dioxane. Fourier transform infrared (FTIR) spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy confirmed the structure of this new monomer. Using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and FTIR spectroscopy, we monitored the curing behavior of Azo-COOH-Py BZ leading to the formation of poly(Azo-COOH-Py BZ); we found that the carboxylic acid and azobenzene units acted as catalysts for the ring opening reaction of the benzoxazine unit. The pyrene moiety of Azo-COOH-Py BZ enhanced the dispersibility of carbon nanotubes (CNTs) in THF, leading to the formation of highly dispersible Azo-COOH-Py BZ/CNT nanocomposites stabilized through π–π stacking of the pyrene and CNT units, as detected through fluorescence emission spectroscopy. We also used DSC and TGA to examine the curing behavior of Azo-COOH-Py BZ/CNTs to form poly(Azopy-COOH-Py BZ)/CNTs nanocomposites. Interestingly, DSC profiles revealed that the maximum exothermic peak representing the ring opening polymerization of the benzoxazine unit of Azo-COOH-Py BZ shifted to much lower temperature upon increasing the content of single-walled CNTs (SWCNTs) or multiwalled CNTs (MWCNTs), suggesting that the CNTs acted as catalysts for the ring opening reaction of the benzoxazine. In addition, the curing temperatures for the SWCNT composites were lower than those for the MWCNT composites, suggesting that the SWCNTs were dispersed better than the MWCNTs in their composites and that the thermal stability of the SWCNT nanocomposites was higher than that of the MWCNT nanocomposites. The combination of photoresponsive azobenzene units, carboxylic acid groups, and CNTs enhanced the thermal stability and char yields of the polybenzoxazine matrixes, as determined through TGA analyses.

Developing hydrogels with excellent mechanical properties and functions is important and challenging. Herein, commercial available materials, polyvinyl alcohol (PVA) and agar, are used to synthesize ultra-strong, self-healable and conductive hydrogels by freezing-thawing cycles and soaking in the ammonium sulfate (AS) solution. The relationship between microstructures and mechanical properties of the obtained PVA-Agar hydrogel is analyzed. The results show that the tensile stress and toughness of PVA-Agar precursor hydrogel are only 0.2 MPa and 0.3 MJ/m3, respectively, due to the uneven network with a pore size between 1 and 8 μm and the lower crosslink density of network. After soaking in AS solution, the network becomes dense and uniform with a pore size of 1–3 μm, accompanied by the formation of stronger hydrogen bonds between PVA and agar. As a result, the tensile stress and toughness increase to 18.0 MPa and 42.3 MJ/m3, respectively. Due to the efficient energy dissipation mechanism endowed by dynamic junctions, the hydrogel also has good anti-fatigue property and high self-healing efficiencies (>80%), and the dissipative energy can reach 18.5 MJ/m3, which accounts for 94.9% of the total energy. Furthermore, the hydrogel exhibits electrical conductivity. The full-fledged starting materials, PVA and agar, and easy-operated process, freeze/thaw cycle, provide our method great potentials to scale up and promising applications as a biocompatible and bioactive material.

In the present work, the blend of poly(butylene succinate) (PBS) and bisphenol A (BPA) was prepared by solution mixing, and the intermolecular interactions between the two components were characterized by a combination of nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The results showed that intermolecular hydrogen-bonding forms between the carbonyl group of PBS and phenol hydroxyl of BPA. With the increase of BPA content, more hydrogen bonds were formed. The effect of hydrogen bonding on the crystallization behavior of PBS was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results showed that the overall isothermal crystallization kinetics and the spherulite growth rate of PBS decrease with the increase of BPA content, while the PBS spherulite size increases with BPA content.

Amorphous poly(vinyl phenol) (PVPh) is introduced into poly(butylene succinate-co-butylene adipate)/poly(l-lactic acid) (PBSA/PLLA) blends via solution casting. Fourier transform infrared spectroscopy (FTIR) analysis verifies that intermolecular hydrogen bonding formed in PBSA/PVPh/PLLA blends. The miscibility between PBSA and PLLA is improved with PVPh incorporation as evidenced by approaching Tgs of the two components. When PVPh content reaches up to 50 wt %, the blend sample exhibits only one Tg, meaning complete miscibility between PBSA and PLLA. The improved miscibility of PBSA/PLLA blends is further confirmed by scanning electron microscope (SEM). Typical “see-island” phase separation structure for PBSA/PLLA blend transforms into homogenous phase structure for blend samples with 5 wt % PVPh and above. Non-isothermal crystallization analysis shows that the crystallization temperature and crystallization enthalpy of PBSA decrease with PVPh addition, and those of PLLA also show a decreasing trend. Isothermal crystallization rate of PBSA in blend samples distinctly decreases with PVPh incorporation, whereas that of PLLA in blend samples increases slightly with PVPh addition. Wide angle X-ray diffraction (WAXD) analysis indicated that PLLA in blend samples remained partly crystallized, while PBSA turned into amorphous state with increasing PVPh contents.

Low crystallization rate and inherent brittleness characteristics limit the wide application of PET. In this paper, it was found that a low molecular weight Phenyl phosphonic acid salts compound (TMC-210) is a very effective nucleator and can enhance the impact strength very much. So, the effect of TMC-210 on the crystallization behaviour and mechanical properties of poly(ethylene terephthalate) were systematically evaluated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD), scanning electron microscope (SEM) and mechanical properties test. The results show that TMC-210 obviously improves the crystallization temperature and accelerates the crystallization rate of PET and reflects a significant heterogeneous nucleating effect with a nucleation efficiency of 99.8 % when introducing a low content of 0.6 wt% TMC-210. The spherulites size and number of blended PET are greater than pure PET. The crystal structure of PET does not change but the blends with high TMC-210 content appears new diffraction peaks in x-ray diffraction spectrogram and it may attribute to the agglomeration of TMC-210 particles, which is verified by SEM observation. The impact fracture surface of PET develops a brittle ductile transition and thus the impact strength of PET improves significantly. Additionally, Lauritzen–Hoffman equation was used to discuss the effect of TMC-210 on the fold surface free energy (σ e) of PET in the crystallization process and found that the σ e values of PET/TMC-210 blends is smaller than that of pure PET.

In this work, 4,4′-Thiobis Phenol (TDP) was incorporated into PLLA using melt blending method. Overall crystallization mechanism and chain folding parameters in crystallization process were analyzed based on Avrami eq. and Lauritzen-Hoffman kinetic theory. Avrami exponent n for all samples were between 2.87 and 3.23, which indicated three dimensional crystal growth with heterogeneous nucleation. Meanwhile, overall crystallization rate of PLLA was significantly reduced by incorporation of TDP. The fold surface free energy (σ e) and work of chain folding (q) increased with TDP addition, implying that crystallization of PLLA was retarded. Small angle X-ray scattering (SAXS) analysis demonstrated that long period of PLLA was increased by TDP introduction, meaning more amorphous component between adjacent lamellae. As a result, the tensile strength decreased with TDP addition, while the elongation at break of PLLA was improved by more than 40 %.

Maleated poly(propylene carbonate)/calcium stearate (MAPPC/CaSt2) composite was prepared through melt-extruding poly(propylene carbonate) (PPC) with maleic anhydride and CaSt2. The processability, thermal stability, interaction between two components as well as the morphology of the composites were systematically characterized. The flow instability of biodegradable PPC was greatly alleviated due to the incorporation of stearate additive in polymer matrix. It was found that the MAPPC and MAPPC/CaSt2 composites were more thermostable than pristine PPC under melt-processing conditions. The melt fluidity of the composites was noticeably superior to that of MAPPC, arising from the lubricating effect of CaSt2 on the polymer/barrel wall interface as well as from the improvement of resistance to thermal degradation of the composite. The coordination interaction between MAPPC and calcium ion also contributes to the enhanced thermal stability and high melt stability of composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The early stage of polymer crystallization may be viewed as physical gelation process, i.e., the phase transition of polymer from liquid to solid. Determination of the gel point is of significance in polymer processing. In this work, the gelation behavior of poly(butylene succinate) (PBS) at different temperatures has been investigated by rheological method. It was found that during the isothermal crystallization process of PBS, both the storage modulus (G′) and the loss modulus (G″) increase with time, and the rheological response of the system varies from viscous-dominated (G′ G″), meaning the phase transition from liquid to solid. The physical gel point was determined by the intersection point of loss tangent curves measured under different frequencies. The gel time (t c) for PBS was found to increase with increasing crystallization temperature. The relative crystallinity of PBS at the gel point is very low (2.5%–8.5%) and increases with increasing the crystallization temperature. The low crystallinity of PBS at the gel point suggests that only a few junctions are necessary to form a spanning network, indicating that the network is “loosely” connected, in another word, the critical gel is soft. Due to the elevated crystallinity at gel point under higher crystallization temperature, the gel strength S g increases, while the relaxation exponent n decreases with increasing the crystallization temperature. These experimental results suggest that rheological method is an effective tool for verifying the gel point of biodegradable semi-crystalline polymers.

The crystallization behavior of n-C(19)H(40)/SiO(2) nanosphere composites was investigated by a combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). Three kinds of confined alkanes with different solid-solid phase transition supercoolings and a surface (or interface) freezing monolayer of n-C(19)H(40) at the bulk liquid/SiO(2) interface were found in the composites at high SiO(2) loading. The surface freezing monolayer induces the chain packing of bulk alkanes by forming a 2D close-packed arrangement without long-range positional ordering in 3D space. A homogeneous nucleation and growth mechanism is found for the solid-solid transition in confined geometry, in which the supercooling of the transition is sensitive to the confined size.