No abstract

Stereocomplex formation between poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) in the melt state was investigated and altered via the addition of multi-branched poly(D-lactide) (PDLA) additives. Two different multi-branched PDLA additives, a 3-arm and 4-arm star-shaped polymeric structure, were synthesized as potential heat resistance modifiers and incorporated into PLLA at 5, 10, and 20 (w/w) through melt blending. Mechanical and thermomechanical properties of these blends were compared with linear poly(L-lactide) (PLLA) as well as with blends formed by the addition of two linear PDLA analogs that had similar molecular weights to their branched counterparts. Blends with linear PDLA additives exhibited two distinct melting peaks at 170-1808C and 200-2508C which implied that two distinct crystalline domains were present, that of the homopolymer and that of the stereocomplex, the more stable crystalline structure formed by the co-crystallization of both D-and L-lactide enantiomers. In contrast, blends of PLLA with multi-branched PDLA formed a single broad melting peak indicative of mainly formation of the stereocomplex, behavior which was confirmed by X-ray diffraction (XRD) analysis. The heat deflection temperature determined by thermal mechanical analysis was improved for all blends compared to neat PLLA, with increases of up to1808C for 20% addition of the 3-arm PLLA additive. Rheological properties of the blends, as characterized by complex viscosity (g*), remained stable over a wide temperature range. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42858.

The steam autoclaving of municipal solid waste followed by size separation was shown to be a way to recover virtually 100% of recyclable poly(ethylene terephthalate) (PET); this is a yield not attainable by a typical material recovery facility. The polymer properties of the recovered PET, which had undergone various degrees of thermal processing, were evaluated by thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, viscometry, and solid-state NMR to assess the commercial viability of polymer reuse. The weight-average molecular weight (M w ) decreased as a result of autoclaving from 61,700 g/mol for postconsumer poly(ethylene terephthalate) (pcPET) to 59,700 g/mol for autoclaved postconsumer poly(ethylene terephthalate) [(apcPET)]. M w for the reclaimed poly(ethylene terephthalate) (rPET) was slightly lower, at 57,400 g/mol. The melting temperature increased with two heat cycles from 236 C for the heat-crystallized virgin poly(ethylene terephthalate) (vPET) pellets to 248 C for apcPET and up to 253 C for rPET. Correspondingly, the cold crystallization temperature decreased with increased processing from 134 C for vPET to 120 C for apcPET. The intrinsic viscosity varied from 0.773 dL/g for the vPET to 0.709 dL/g for rPET. Extruded samples were created to assess the potential commercial applications of the recovered rPET samples. The M w values of the extruded apcPET and rPET samples dropped to 37,000 and 34,000 g/mol, respectively, after extrusion (three heat cycles); this indicated that exposure to heat dictated that these materials would be better suited for downcycled products, such as fibers and injected-molded products.

In this study, the enhancement of the biodegradation rate of polylactic acid (PLA) filled with commercially available soil amendment product (NTM) or a nanoclay (Cloisite 25A) were evaluated. Cloisite 25A and NTM were incorporated into PLA at 5, 10, 20 (w/w) through melt blending. Transmission electron micrographs revealed particles with a wide range of sizes that were formed by clumping of many smaller particles. The particles showed good dispersion in PLA by scanning electron microscopy. Under standard composting conditions using a standard technique for aerobic biodegradation of plastic materials, it was shown that the addition of NTM enhanced the biodegradation rate of PLA composites by 3-to 4-fold compared to neat PLA. Linear kinetics were used to obtain induction periods, half-lives, and rates of mineralization. Finally, mechanical and thermomechanical properties of these blends were compared with PLA. Published 2020. This article is a U.S. Government work and is in the public domain in the USA. J. Appl. Polym. Sci. 2020, 137, 48939.