This is an editorial article. It has no abstract.

A set of complementary experiments are used for the first time to elucidate the interrelation between the mechanical properties, the strain field, and the free volume evolution during non-homogenous compression of a glassy polymer. Two sets of quenched and annealed polystyrene samples, having different free volume histories, are notched and exposed to compression. The variation of both the strain field and the free volume are measured on a microscopic scale via digital image correlation in case of strain and Doppler broadening spectroscopy of positron annihilation line in case of free volume measurements. Eventually, the interplay between the local evolution of free-volume, the local strain field, and the mechanical response is investigated throughout the yielding, softening and plateau regions. We found that in all stages of plastic deformation the generated local strain field is positively correlated to the global strain independent of the active mechanism of plastic deformation. Moreover, the local change of free volume is not correlated to the mechanical response of the polymer at the softening stage. Therefore, the free volume evolution should not be responsible for the intrinsic post-yield softening behavior. The easy flow in the plateau region, however, begins at a particular fraction of free volume independent to the thermal history of samples.

The high cost and less variety of raw materials has greatly restricted the wide application of selective laser sintering (SLS) technology. In order to make the material cheaper and more diverse, PA6 is the most preferable material. In this work, a new PA6/SiO₂ composite microsphere used for SLS was designed and fabricated. To construct the material, PA6 porous microspheres with diameters of 20–80 µm and a certain pore volume were firstly prepared by the dissolution precipitation method. Then, SiO₂ was generated in situ in the PA6 porous microsphere framework, thus achieving a special structured PA6/SiO₂ composite microsphere. These microspheres with much well dispersed SiO₂ in PA6 matrices formed a powder with high bulk density and good electron conductivity. The particle size and weight fraction of the two components can be well controlled by adjusting the experimental conditions. Differential scanning calorimetry (DSC) data showed that the composite powder had a larger sintering window, which would be beneficial for SLS processing. The introduction of SiO₂ reduced the rate of water absorption in the composite powder, which could improve the accuracy of SLS forming. This work has certain significance as a reference for the design and development of SLS polymer-based composite materials.

Reactive extrusion is a cost-effective and environmentally-friendly method to produce new materials with enhanced performance properties. At present, reactive extrusion allows in-situ polymerization, modification/functionalization of polymers or chemical bonding of two (or more) immiscible phases, which can be carried out on commonly used extrusion lines. Although reactive extrusion has been known for many years, its application for processing of bio-based polymer blends and composites is a relatively new direction of scientific research. This work presents a literature review on recent advances in the processing of bio-based polymer blends and composites via reactive extrusion. We described compatibilization mechanisms for different types of biodegradable polymeric materials based on: (i) aliphatic polyesters, (ii) aliphatic polyesters/starch and (iii) aliphatic polyester/natural rubber systems. A special attention was focused on conventional and dynamic cross-linking of bio-based polymer blends and composites as an effective way to prepare new materials with unique properties e.g. biodegradable thermoplastic elastomers or shape-memory materials. Advantages and limitations affecting future trends in development of biodegradable polymer blends and composites reactive extrusion are also discussed.

Bio-based blend nanocomposites of poly(L-lactic acid) (PLLA) and poly(butylene succinate) (PBS), with different concentrations (from 0.1 to 0.5 wt%) of graphene oxide (GO), are prepared via solution dispersion of PBS/GO followed by melt blending with PLLA in a 70/30 PLLA/PBS weight ratio. Scanning and Transmission Electron Microscopy reveals micron-sized droplets of PBS in the PLLA matrix with the GO nanofiller preferentially found in the PBS phase. The GO acts as nucleating agent for both semicrystalline polymers. The nanofiller nucleating effect is compared to the one of own selfnuclei for each polymer, to define a convenient nucleating efficiency (NE) scale. A value of around 80% is determined for GO towards PBS, among the highest NEs ever reported for this polymer. On the other hand, the efficiency in nucleating PLLA is equal to a modest 15%, also due to the uneven distribution of the nanofiller in the two polymers. A close relationship between the nanocomposite morphology and crystallization behavior of the two different polymers is thus established.

A novel gold/aniline-pentamer-based electroactive polyamide (Au/EPA) composites that can modify carbon paste electrodes (CPEs) for ascorbic acid (AA) sensing has been studied in detail in this article. Cyclic voltammetry studies indicated improved electrochemical properties of the Au/EPA composites, demonstrating the occurrence of efficient electron/charge transfer between the Au and the EPA. Experimental tests shows that there is a linear relationship between the concentration of added AA and the response current for the CPE modified with Au/EPA sensor to the concentration of AA in the range of 0.05–0.75 mM (R² = 0.996, n = 15). The detection limit and the sensitivity of the Au/EPA-CPE AA sensors were 2.75 µM at a signal to noise ratio (S/N) of 3, and 21.7 mA·mM^–1, respectively.

The thermal behavior and pyrolytic kinetic analysis of main waste polymers (polypropylene (PP), polyethylene film (PE), poly(ethylene terephthalate) (PET), polystyrene (PS)) and three synthetic mixtures representing commingled postconsumer plastics wastes (CPCPWs) output from material recovery facilities were studied. Thermogravimetry (TG) pyrolysis experiments revealed that the thermal degradation of single polymers and the synthetic mixture enriched in PP occurred in one single step. The other two mixtures underwent a two-consecutive, partially overlapping degradation steps, whose peaks related to the first-order derivative of TG were deconvoluted into two distinct processes. Further TG experiments carried out on binary mixtures (PS/PP, PET/PP, PET/PEfilm and PP/PEfilm) showed a thermal degradation reliance on composition, structure and temperatures of single polymer components. A kinetic analysis was made for each step using the Kissinger-Akahira-Sunose (KAS) method, thus determining almost constant activation energy (E_a) for pyrolysis of PS, PET, PP and PE film in the range 0.25<α<0.85, unlike for pyrolysis of CPCPWs, with particular reference to CPCPW1 and the second step of CPCPW2 and CPCPW3, both ascribable to degradation of PP and PE film. To account for the reliability of these values the integral isoconversional modified method developed by Vyazovkin was also applied.

Application of human mesenchymal stem cells brings a new hope for advanced wound healing. To enable cells culture and their viability maintenance, a new type of biomaterials must be developed. Scaffolds prepared from polymers of natural origin can mimic extracellular matrix. Chitosan, which is a chitin derivative, has many favorable properties like biodegradability or lack of cytotoxicity. Therefore, it is widely applied in medicine and pharmacy. Nevertheless, its chemical modification may lead to the loss of biocompatibility of the material and generate some significant problems with cells culture. In this article a novel strategy of the bioactive and antimicrobial chitosan hydrogel scaffolds is presented. As crosslinking agents non-toxic substances were used such as aspartic acid and glutamic acid. Obtained biomaterials were investigated over their chemical structure, morphology and biological activity. Performed tests using human mesenchymal stem cells confirmed bioactivity and biocompatibility, as well as antibacterial and antifungal properties.