This is an editorial article. It has no abstract.

Poly(lactic acid) (PLA) synthesized from renewable resources has drawn a great deal of interest in packaging, electronics and automotive applications. However, poor flame retardancy of PLA, especially its ease of ignitability and heavily flaming drips, represents a major obstacle for its potential application. The article outlines the recent advances in the field of flame-retarded PLA. Current development trends based on the direct incorporation of flame retardant additives, chemical modification, hybridization and synthesis of flame retardants were reported. Results obtained from UL 94 vertical burning, limiting oxygen index (LOI) and cone calorimetry (CCM) tests for each type of flame retardants were discussed and analyzed. Test results summarized in a UL 94-LOI matrix found to be a useful tool to determine the effectiveness of flame retardants in PLA. The UL 94-LOI comparison matrix and CCM test results revealed that the combined use of flame retardants (containing intumescent formulation) is one of the promising strategies to reach the flame retardancy of PLA needed by practical applications. This review ends with a brief summary of and outlook on future developments of flameretarded PLA systems.

Graft copolymers from commercial chlorinated polypropylene (PP-Cl) possessing either poly(ethylene glycol) (PEG) or poly(ε-caprolactone) (PCL) grafts are synthesized by copper (I)-catalyzed azide-alkyne cycloaddition ‘click’ reaction (CuAAC). For this purpose, azido-functional polypropylene is prepared by nucleophilic substitution of chlorine groups of PP-Cl with azidotrimethylsilane-tetrabutylammonium fluoride. Whereas, the clickable alkyne end-functional PEG and PCL are independently synthesized by esterification reaction of poly(ethylene glycol) methyl ether with 4-pentyonic acid at room temperature and ring-opening polymerization of ε-caprolactone using stannous octoate as catalyst and propargyl alcohol as initiator. Finally, the corresponding graft copolymers, PP-g-PEG and PP-g-PCL, with different surface properties were successfully synthesized by CuAAC ‘click’ reaction under mild condition. Spectral, chromatographic and thermal analyses at various stages prove the formation of desired polypropylene-based graft copolymers with well-defined properties. Furthermore, the water contact angle values of PP-Cl, PP-g-PEG and PP-g-PCL are found as 90±1°, 78±1.8° and 83±2.1°, respectively.

Several commercially available thermoplastic biopolymers were processed in a continuous extrusion line. The molecular weight, crystallinity, and mechanical and permeation properties of the cast films were determined in order to evaluate the status quo of biopolymers currently commercially available. The biopolymers that were evaluated were polylactic acid (PLA), several polyhydroxyalkanoates (PHAs) (Poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHBHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)), thermoplastic starch (TPS), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polycaprolactone (PCL) and biobased polyethylene (BioPE). Due to its potential for biobased production, thermoplastic polyurethane elastomer (TPU) was also analysed. Mechanical analysis showed the PLA and PHA films had high strength and extremely low elongation at break. These were also the materials with the highest molecular weights. Films made of TPU, PCL, TPS, PBAT and BioPE had a significantly lower Young’s modulus and significantly higher elongation at break; these films had comparatively low molecular weights. Permeation measurements showed that PHA films, and particularly PHBV, had the lowest oxygen and water vapour permeability of the biopolymers that were analysed. The biopolymers BioPE, TPS, PCL, TPU and PBAT were highly permeable to oxygen, and had comparatively low molecular weight. The biopolymers TPU, PBS, PBAT, PCL and TPS were highly permeable to water vapour.

Polymer-based electrospun amorphous solid dispersions (ASDs) were prepared and investigated from pharmaceutical application point of view. Spironolactone (SPIR) was used as model drug mixed in various concentrations with polymers suitable for fibre formation, such as vinylpyrrolidone-vinyl acetate copolymer, polyvinylpyrrolidone K30 and hydroxypropyl methylcellulose. Single needle electrospinning was applied at first for screening the composition of the prepared ASDs. Scaling-up the selected polymer-drug combination was accomplished by high speed electrospinning, the productivity of which enabled investigation of downstream processing to generate tablet formulation. The steps of a potential continuous production line (fibre collection, grinding, feeding and tableting) proved to be feasible with the electrospun ASD without any sign of crystallization. If crystalline drug was added into the ASD containing tablets as impurity strictly monotonous decrease of drug dissolution was observed in the function of the crystalline drug content. The capabilities of the non-destructive Raman and near-infrared spectroscopies, as fast quality assurance tools, were compared to each other in quantifying of crystalline SPIR content in the prepared tablets.

A synthetic procedure is described for preparation of magneto-sensitive nanocomposites from maghemite nanoparticles and a natural polysaccharide, sodium alginate cross-linked with calcium ions. With this procedure, a series of nanocomposites was synthesized and characterized by spectrophotometry, transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy, Fourier transform IR-spectroscopy and magnetometry with the following main conclusions: (a) The nanocomposites retain their solubility in water unless the iron content exceeds 18.1±0.2 wt%. (b) Only γ-Fe₂O₃ nanoparticles are included in the nanocomposite. (c) Size of nanoparticles lies within a 4–20 nm range with a dominant diameter of 7±1 nm. (d) Maghemite nanoparticles bind to the alginate matrix via formation of electrostatic and coordination contacts between the surface Fe³⁺ maghemite ions and functional alginate groups. (e) The nanocomposites exhibit properties which are characteristic for soft magnetic materials since they have a low coercive force. (f) Magnetic characteristics of the nanocomposites, saturation magnetization and residual magnetization, are effectively controlled by the maghemite content. (g) An external magnetic field causes the nanocomposites to move in an aqueous dispersion.

This paper represents the first report of thermoplastic starch (scCO₂TPS) and glutaraldehyde (GA) modified TPS resins (scCO₂TPS₁₀₀GA_x), gelatinized and/or modified with the aid of supercritical carbon dioxide (scCO₂). The melt flow rate, initial and retention values of tensile strength (σ_f) of TPS and GA-modified TPS prepared using scCO₂ fluid were considerably higher than those of TPS and TPS₁₀₀GA_x materials prepared in the conventional way. After conditioning at 20 °C/50% RH for 56 days, the σ_f of properly prepared scCO₂TPS₁₀₀GA_0.1 still remained at 17.5 MPa, which is around 3.5 times of that of the corresponding conditioned TPS₁₀₀GA_0.1. The moisture contents of conditioned scCO₂TPS and scCO₂TPS₁₀₀GA_x were considerably lower than those of the corresponding TPS and TPS₁₀₀GA_x aged for the same amounts of time. Conditioned scCO₂TPS andscCO₂TPS₁₀₀GA_x exhibited only V_h-type crystals with melting temperatures ~20°C lower than those of corresponding conditioned TPS and TPS₁₀₀GA_x. In comparison to TPS and TPS₁₀₀GA_x, more dissociated amylopectin chains with loosely hydrogen-bonded –OH groups and significantly less retrogradation was found for conditioned scCO₂TPS and scCO₂TPS₁₀₀GA_x.

A series of aromatic polyimides has been obtained by the reaction of two dianhydrides, the commercial 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and another having a 5′-tert-butyl-m-terphenyl moiety (BTPDA), with several diamines, including two that have a cardo structure (derived from 9H-fluorene), one of them bearing methyl groups ortho to the amino functionalities (TMeCardo). The solubility, and also the thermal, mechanical, and gas separation properties of the corresponding polyimide membranes were evaluated and compared in order to explore the effect of the different groups in the polyimide backbone. The novel polyimides, which were derived from BTPDA and the cardo diamines, showed high thermal stability, excellent solubility in organic solvents and good gas separation properties, especially the polyimide that bore the ortho methyl substituents. The behavior was especially good for the pair O₂/N₂, where the TMeCardo polymer overpassed the Robeson upper bound.