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Lignin-capped silver nanoparticles were incorporated in situ into polyurethane foams during their polymerization to obtain multifunctional materials suitable for chronic wound dressing. Lignin with increased phenolic content, achieved through the enzymatic grafting of natural phenolic compounds, played the dual role of a silver reducing agent in the synthesis of the lignin-capped silver nanoparticles and as a nanoformulated polyol additive in the polyurethane composition able to react with isocyanate. The nanoparticles-embedded polyurethane foams showed over 4 and 5 logs bacterial growth reduction against the Gram-positive S. aureus and the Gram-negative P. aeruginosa, respectively, attributed to both the direct contact- and release-killing mechanisms. The swelling properties of the foams, related to their capacity to remove the excess of wound exudates containing deleterious oxidative species and enzymes, varied from 585 to 1145 % as a function of the content of nanoparticles. Overall, the physicomechanical and antibacterial properties of the foams, together with their biocompatibility and sustained release of silver, make these multifunctional materials suitable candidates for chronic wound dressings.

This work presents the experimental results of the mechanical and fracture behaviour of three polymeric blends prepared from two recycled plastics, namely polypropylene and opaque poly (ethylene terephthalate), where the second one acted as a reinforcement phase. The raw materials were two commercial degrees of recycled post-consumer waste, i.e., rPP and rPET-O. Sheets were manufactured by a semi-industrial extrusion-calendering process. The mechanical and fracture behaviours of manufactured sheets were analyzed via tensile tests and the essential work of fracture approach. SEM micrographics of cryofractured sheets revelated the development of in situ rPP/rPET-O microfibrillar composites when 30 wt.% of rPET-O was added. It was observed that the yield stress was not affected with the addition of rPET-O. However, the microfibrillar structure increased the Young’s modulus by more than a third compared with rPP, fulfilling the longitudinal value predicted by the additive rule of mixtures. Regarding the EWF analysis, the resistance to crack initiation was highly influenced by the resistance to its propagation owing to morphology-related instabilities during tearing. To analyze the initiation stage, a partition energy method was successfully applied by splitting the total work of fracture into two specific energetic contributions, namely initiation and propagation. The results revelated that the specific essential initiation-related work of fracture was mainly affected by rPET-O phase. Remarkably, its value was significantly improved by a factor of three with the microfibrillar structure of rPET-O phase. The results allowed the exploration of the potential ability of manufacturing in situ MFCs without a “precursor” morphology, providing an economical way to promote the recycling rate of PET-O, as this material is being discarded from current recycling processes.

This work provides an experimental analysis regarding the fracture behavior of recycled opaque PET (rPET-O) containing titanium dioxide (TiO2) under plane stress conditions. For this purpose, a commercially post-consumer transparent colored/opaque PET flakes mix was processed using a semi-industrial extrusion calendering process. The manufactured rPET-O sheets had a TiO2 content of 1.45 wt.%. The mechanical and fracture properties of unaged and physically aged (1 year) samples were determined through uniaxial tensile experiments and the Essential Work of Fracture (EWF) methodology, respectively, and were compared to those of recycled transparent PET (rPET-T). Under tensile loading, independently of the aging time, rPET-O samples exhibited similar mechanical behavior as rPET-T up to the yield point. The main differences remained in the post-yielding region. The presence of TiO2 particles allowed reducing the strain energy density up to neck formation in aged samples. Regarding the EWF analysis, it is argued that the energy consumed up to the onset of crack propagation (we) for rPET-T was mainly dependent of the molecular mobility. That is, the we value decreased by 26% when rPET-T was physically aged. Interestingly, we values remained independent of the aging time for rPET-O. In fact, it was highlighted that before crack propagation, the EWF response was principally governed by matrix cavitation ahead of the crack tip, which allowed a significant release of the triaxial stress state independently of the molecular mobility. This property enabled rPET-O to exhibit a resistance to crack initiation 17% higher as compared to rPET-T when the material was physically aged. Finally, independently of the aging time, rPET-O exhibited a resistance to crack growth approximately 21% larger than rPET-T due to matrix fibrillation in large scale deformation.

Adding textures to surfaces is known to improve the external appearance of injection moulded components. However, when high surface quality is required, normally a paint coating is applied on top of the moulded textured surface. In this work, an alternative to painting for obtaining high quality surfaces is proposed, following an environmental-friendly process and having low production cost. Three different surface textures obtained by injection moulding have been characterized and compared with a painted one. Alternative topographical parameters such as the absolute functional height (AFH), the functional height distribution (FHD), texture slope (TS) or texture aperture angle (TAA) besides to the traditional roughness parameters such as the arithmetical mean height (Sa) and the root mean square height (Sq) have been utilized to characterize the random surface textures. The relationships between these parameters and the surface quality appearance represented by gloss and reflectivity contrast have been established using a new total appearance measurement (TAM) apparatus. It was found that by applying secondary operation on the textured mould cavity, such as adding micro roughness features or coatings, equal apparent quality to the ones obtained by painting can be reached.

PLA bio-blends with a predominantly biosourced PA10.10 in the composition range 10-50wt.% were prepared by melt blending in order to overcome the advanced brittleness of PLA. Due to the inherent immiscibility of the blends, 30 wt.% of PA was needed to achieve a brittle-to-ductile transition and a co-continuous morphology was predicted at 58 wt.% of PA. The initial enhancement of the PLA rheological behaviour through the environmentally friendly reactive extrusion process yielded a finer and more homogeneous microstructure and hence enhanced the mechanical properties of the bio-blends at much lower PA contents. The brittle-to-ductile transition could be achieved with only 10 wt.% and co-continuity was observed already at 44 wt.% of PA. Results indicate the significant potential of modifying PLA flow behaviour as a promising green manufacturing method toward expanding PLA-based bio-blends applications.

Square plates (nominal thickness: 3 mm, nominal width: 100 mm) of different rheologically modified PLA/ABS blends were manufactured through injection molding, with or without adding ABS grafted with maleic anhydride (MAH). During processing, the properties of the melt were stabilized and enhanced by the addition of a styrene-acrylic multi-functional-epoxide oligomeric reactive agent (SAmfE). PLA-REX was obtained by reactive extrusion of PLA. A general analytical equation was used in order to evaluate the kinetic parameters of the thermal degradation of PLA−REX/ABS and PLA−REX/ABS/ABS−g−MAH blends through thermogravimetric analysis. The thermal degradation of these blends occurred through two different reaction steps. Various empirical and theoretical solid-state mechanisms were tested to elucidate the best kinetic model. In order to reach this goal, plots of standardized conversion functions were constructed. Given that it is not always easy to visualize the best accordance between experimental and theoretical values of standardized conversion functions, a recently proposed index was determined to quantitatively identify the best mechanism. By doing that, it has been possible to determine the right activation energy of the thermal degradation. It has been demonstrated that the best mechanisms for these materials were R2 (i.e. phase-boundary-controlled reaction (contracting area)) for the first step (α 70%). The thermal stability of PLA−REX/ABS blend was greatly improved by adding the ABS−g−MAH compatibilizer. These findings were also confirmed by means of morphological characterization through scanning electron microscopy.

Lightweight bio-based aerogels from sustainable gum Arabic (GA) and sodium montmorillonite (Na+-MMT) clay were prepared by means of a simple freeze-drying process. GA/clay aerogels showed high porosity (87.9%–94.9%) of mainly open type and the mechanical properties were improved by the clay. When 40% of clay was added to pure GA, the specific modulus and the absorbed energy of resultant aerogels increased by 1.6 and 4.2 times respectively. On the other hand, the exponent value for modulus in the power-law model for cellular materials increased from 1.95 to 3.28 due to the more anisotropic structures induced by the presence of the clay. In terms of thermal stability and flame retardancy, clay content played a dominant role. With 50% of clay loading, the initial decomposition temperature increased by nearly 16 °C and the peak of heat release rate was 3-fold reduced.

In this work, the relations between the replication quality of random, coarse textured, surfaces with the injection-moulding process has been analysed through 3D areal characterisation techniques. The multi-scale surface approach has been applied to effectively separate the main surface components, roughness, waviness and form. Amplitude, functional, hybrid and spatial parameters, as well as alternative surface characteristics such as the number of micro-cavities (NG), grain area ( G A ¯ ) and grain volume ( G V ) , ¯ were used as a way to determine the influence of the manufacturing process on the replication quality of the mould texture, either at the macro- or micro-scale. A model to quantify the effect of the injection-moulding parameters on surface texture replication has been obtained through a 24 factorial design of experiments. It was found that the holding pressure was the main parameter to enhance the mould texture replication, followed by the melt and mould temperatures. The injection volumetric flow rate did not have a significant effect on the texture replication ratio. The surface analysis, at the human eye resolution, only allows the detection of macro-defects such as form deviation. On the other hand, the surface characterisation at the micro-scale allows the detection of roughness differences, up to 30% on average, as a function of the injection conditions.

In this research, the influence of the macro- and micro-topography on randomly micro-textured polypropylene surfaces has been studied. An initial characterization of the underlying surface was carried out using three-dimensional (3D) technologies such as chromatic and white light confocal microscopy. A multi-scale analysis methodology was employed for analysing the surface at either macro- or micro-scales. Among others, topographic characteristics such as peak-to-valley symmetry and the amount of micro-asperities were analysed to quantitatively determine the scratch and mar visibility resistance. The results show that surfaces with higher symmetry in their functional height distributions yield lower lightness variation (¿L*) between the scratch pattern and its residual background height (RBH). This allows for a better suitability in hiding the scratch damage. On the other hand, topographies with less amount of micro-asperities on top of the texture provided a better mar resistance. In these cases, deformation mechanisms such as ironing are minimized, resulting in a lower gloss variation and lower contrast between the damaged area and its surroundings.

A series of low density, highly porous clay/poly(vinyl alcohol) composite aerogels, incorporating ammonium alginate, were fabricated via a convenient and eco-friendly freeze drying method. It is significant to understand rheological properties of precursor gels because they directly affect the form of aerogels and their processing behaviors. The introduction of ammonium alginate impacted the rheological properties of colloidal gels and improved the mechanical performance of the subject aerogels. The specific compositions and processing conditions applied to those colloidal gel systems brought about different aerogel morphologies, which in turn translated into the observed mechanical properties. The bridge between gel rheologies and aerogel structures are established in the present work.

Low density composites of sodium montmorillonite and poly(amide-imide) polymers have been created using an ice templating method, which serves as an alternative to the often-difficult foaming of high temperature/high performance polymers. The starting polymer was received in the poly(amic acid) form which can be cured using heat, into a water insoluble amide-imide copolymer. The resulting materials have densities in the 0.05 g/cm3 range and have excellent mechanical properties. Using a tertiary amine as a processing aid provides for lower viscosity and allows more concentrated polymer solutions to be used. The concentration of the amine relative to the acid groups on the polymer backbone has been found to cause significant difference in the mechanical properties of the dried materials. The synthesis and characterization of low density versions of two poly(amide-imide) polymers and their composites with sodium montmorillonite clay are discussed in the present work.

In this work, microcellular ABS foams were studied. A series of injection molding samples defined by a design of experiments was carried out to analyze the effect of shot volume, mold temperature, and injection velocity on the morphology, mechanical properties, and surface roughness of microcellular samples. A predominant influence of shot volume on the cell structure and tensile properties was evidenced. Higher cell densities and narrower cell size distributions were obtained at lower injection volume. However, elastic modulus and tensile strength were improved by increasing the shot size. The effect of mold temperature and injection velocity was secondary. Higher levels of mold temperature and injection rate provided finer cell morphologies, but their effects on the elastic modulus and tensile strength were negligible. The decrease in shot volume and increase in gas content led to poor surface quality, whereas it was greatly improved by raising both mold temperature and injection velocity

A facile cross-linking strategy to construct flame retardant cellulose nanofibril (CNF)/sodium montmorillonite (MMT) aerogels with improved mechanical properties, by incorporating melamine-formaldehyde (MF) resins into precursor suspensions followed by a freeze-drying process, is reported in this work. Scanning electron microscopy images indicate that MF cross-linking does not significantly change the microstructures of CNF and CNF/MMT aerogels. However, the cross-linking improves the materials’ mechanical and flame properties. By incorporating 50 wt% of MF, the compression moduli and compressive stress of CNF aerogels increase by 316% and 114%, respectively. The limiting oxygen index (LOI) value of CNF aerogels also increases from 17.1% to 23.4%. Further addition of MMT increases the CNF aerogels’ LOI value to 57% and increases the maximum decomposition temperature by nearly 20 °C. This occurs because MMT and MF induce a synergistic effect which improves the flame retardant properties of the CNFs aerogels. In CNF/MMT composite aerogels, the introduction of 34 wt% of MF leads to a 54.6% reduction of the peak of heat release rate and a 53.2% decrease in total heat release. CNF aerogels made from sustainable feedstocks with excellent mechanical properties and high flame retardancy, like those discussed herein, show promise as fire resistant biofoams

Double edge notched tension (DENT) specimens of a polyethylene terephthalate (PET) film were tested in an universal testing machine, measuring the displacements and the ligament lengths with a digital image correlation (DIC) system. With these data the essential work of fracture (EWF), crack tip opening displacement (CTOD), and the J-integral fracture methods were compared. The specimens were tested in mode I under plane stress conditions, verifying that the crack always propagated through a fully yielded ligament. It has been proved that w e , the specific essential work of fracture was the specific energy just up to crack initiation and has the same value that J-integral at crack initiation, J o . The relationship of these parameters with the CTOD was also shown. The influence of the notch quality on the fracture behaviour when the specimens were sharpened by two different methods, femtosecond laser ablation or by razor blade sliding, has also been analysed in detail.

Square plates (nominal tickness: 3 mm, nominal width: 100 mm) of diferent rheolgically modified PLA/acrylonitrile-butadiene-styrene (ABS) blends were manufactured through injection molding process. During processing, the properties of the melt were stabilized and enhanced by the addition of a styrene-acrylic multi-functional-epoxide oligomeric reactive agent (SAmfE). The general analytical equation has been used in order to evaluate the kinetic parameters of the thermal degradation of PLA-REX, ABS and its bioblend with a weight content of 70/30. Various empirical and theoretical solid-state mechanisms have been tested to elucidate the best kinetic model. In order to reach this goal, activation energy values were calculated by means of the Kissinger–Akahira–Sunose method. On the other hand, the standardized conversion functions have been constructed. Given that it is not always easy to visualize the best accordance between experimental and theoretical values of standardized conversion functions, a recently proposed index has been determined to quantitatively support our findings relative to the best reaction mechanisms. It has been demonstrated that the best mechanism for the thermal degradation of PLA-REX and ABS was the random scission of macromolecular chains. The bioblend thermal degradation occurred in two steps: the first step (α < 60%) took place through an R2 mechanism whereas the second step (α > 75%) did it according an F3 mechanism. Moreover, y(α) master plots have also been used in order to confirm that the selected reaction mechanisms were adequate The Ministry of Economy and Competitiveness projects MAT2013-40730-P and MAT2016-80045-R (AEI/FEDER, UE) of the Spanish Government financially supported this work

A unique set of double-edge notched tension specimens of a Polyethylene Terephthalate Glycol-modi¿ed ¿lm was tested in mode I, plane stress. The load was registered on a universal testing machine. The displacements, ligament lengths, and video frames were recorded by a Digital Image Correlation system. With these registered data, the essential work of fracture, J-integral, and crack tip opening displacement (CTOD) fracture concepts have been applied. The onset of crack initiation was through a complete yielded ligament. The analysis showed that the intrinsic speci¿c work of fracture, we, is the speci¿c energy just up to crack initiation, which is an initiation value. we has both a coincident value and the same con-ceptual meaning as Jo, the J-integral at the onset of crack initiation. The relationship between Jo and CTOD is also determined. The in¿uence on the notch quality when the specimens were sharpened by two different procedures, femtosecond laser ablation and razor blade sliding, was analysed in detail.

Both inorganic and polymeric aerogels are well-known in the materials field. Inorganic aerogels are generally susceptible to brittle fracture, while polymeric aerogels tend to exhibit low modului and high flammability. To overcome these disadvantages, we introduce a new approach to the design of aerogels. A microporous poly(vinyl alcohol) (PVA) aerogel/silica nanocomposite was prepared by growing a silica conformal coating onto a PVA aerogel scaffold. Such aerogel/silica nanocomposites show significant improvement in their mechanical properties over either individual component. The nanocomposites show excellent fire resistance since the silica conformal coating serves as a barrier for heat transfer and mass loss of the coated organic materials. After a fluorocarbon silane treatment, the nanocomposites also show durable superhydrophobicity.

Cyclic butylene terephthalate (CBT®) oligomers are a relatively new class of material and are capable of polymerizing in an entropically driven ring-opening polymerization into high-molecular-weight polymerized CBT (pCBT) in very short times, i.e., within minutes. The most important feature of CBT is its very low, water-like melt viscosity prior to polymerization which gives rise to an excellent impregnation of fibrous reinforcements in contrast to conventional, high viscous thermoplastic resins. This opens up new possibilities in the thermoplastic composite production since thermoplastic-based composites show some advantages over thermoset-based ones. Specifically, they have a higher toughness and impact strength and they can be welded, postformed, and recycled due to their thermoplastic nature. CBT has the potential to substitute thermoset matrices in fiber-reinforced composites and may solve some of the today´s recycling issues associated with thermoset-based composites. Moreover, the low melt viscosity of CBT enhances the dispersion of nano- or conductive particles and can yield superior nano- and conductive composites. This article reviews the recent advances in processing–structure–property relationship, physical and chemical modification of pCBT, as well as the preparation of fiber-reinforced pCBT composites, pCBT nanocomposites, and conductive pCBT composites.

In the present work, poly(lactic acid) (PLA) sheets reinforced with organically modified montmorillonite (o-MMT) were manufactured through reactive extrusion-calendering using a masterbatch approach in a pilot plant. Reaction monitoring analysis suggests the occurrence of premature reactions between o-MMT and the reactive agent; lowering further structural changes in the polymeric matrix. While calendered sheets exhibited a homogenous and preferential distribution of clay particles in MD, the coexistence of mixed structures, involving tactoids of various sizes as well as intercalated clay layers was observed. However, a higher and finer dispersion of o-MMT particles was achieved through clay–polymer tethering via chain extender molecules. Under tensile loading, the aforementioned clay dispersion enhanced multiple cavitation processes, notably improving PLA shear flow.

In this work, the properties of microcellular ABS were studied. Foamed samples exhibited a solid skin/foamed core struc- ture, with some elongated cells in the flow direction, while spherical cells were mostly observed in the transversal direction. The flex- ural modulus, flexural strength, and fracture toughness K Ic decreased with the density. However, the crack tip opening displacement (CTOD) was found to increase with the foaming ratio. The evolution of the mechanical properties and fracture toughness was well described by prediction models considering the skin/core morphology of these microcellular materials. Foaming increased the aniso- tropic behavior of the material, due to the cell elongation caused by the fountain flow during injection

Fracture and thermal behavior of injection-molded poly (ethylene terephthalate-co-isophthalate) filled with milled glass fiber has been studied as a function of fiber content in the range 0-40% by weight. Composite Young's modulus and tensile strength increased with fiber percentage, and good agreement was found with theoretical predictions. Low rate fracture tests were carried out on injection-molded SENB specimens. Fracture toughness ( K ic ) and fracture energy ( G ic ) could be obtained by applying Linear Elastic Fracture Mechanics (LEFM). Results seemed to indicate improved fracture toughness if compared with homopolymer poly (ethylene terephthalate) composites. The reason was attributed to a lower crystallinity developed in the matrix, which promoted higher plastic strain.

Films of an architecturally modified poly(lactic acid) (PLAREx) with three different types of fumed silica nanofillers (SiO2) were processed through reactive extrusion-calendering in a pilot plant. The effects of the SiO2 type on both the dispersion and the crystallization behaviour under dynamic and isothermal conditions are investigated using transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The mechanical properties are assessed by tensile testing. TEM micrographs showed that the improved chemical affinity of both surface-treated SiO2 towards PLAREx end groups did not improve particle dispersion. DSC results revealed that untreated SiO2 nucleated PLAREx more efficiently than both surface-modified silicas. The activation energy for the isothermal crystallization process, as determined by an Arrhenius method, suggests that addition of untreated SiO2 enhances the crystallization rate of PLAREx. However, it seems that the tensile behaviour remained unchanged whether silicas were added or not.