Structural evolution in propylene-based elastomer with γ form during stress relaxation

Enhancing biodegradation of polyolefins and real mixed plastic waste by combination of pretreatment and mixed microbial consortia

Polyolefins (PO)1 are the most common consumer plastics, constituting about half of plastic waste. This work investigated the process combining physicochemical pretreatment and PO-enriched mixed microbial consortia (MMCs) on biodegrading European real mixed plastic waste. The MMCs, acclimatized on PO powders, were enriched with strains that could use PO, primarily dominated by the genus Rhodanobacter. Several pretreatment methods were investigated on pure polyethylene (PE) and polypropylene (PP). UVC combined with Fenton's reagent was found to be the best pretreatment process for pure PO, increasing the total oxidative indices of PE and PP by 135 and 21 times, respectively, and decrease the total crystallinity of PP by 2.3 times (but not PE), compared to the untreated ones. Maximum 7.7% and 16.3% weight reductions were achieved after MMCs biodegradation of UVC-Fenton-treated PE and PP powders (80 μm), with a 4.3- and 27.2-times improvement from the untreated ones. Selected pretreatments and MMCs were then applied to real mixed plastic waste and post-consumer multilayers from 10 different streams. The highest weight reductions after 30-days biodegradation were obtained using mixed plastic reject from a biogas plant (MW2) followed by the unrecyclable mixed plastic waste from a Danish municipality (MW1), with a reduction of 36.8% and 30.0% using radio frequency (RF) oxygen plasma pretreatment, respectively. Integration of ultrasonic irradiation with atmospheric pressure plasma treatment increased the biodegradation of MW1 to 39.4%. This study addressed the bottleneck of slow biodegradation of recalcitrant plastics, laying down the basis for future development of biotechnological recycling of unrecyclable plastic fractions.

Specific deformation behavior of isotactic polypropylene films under a multiaxial stress field

The specific deformation behavior of crystalline polymer films, namely unoriented crystallized isotactic polypropylene (it PP) films, was investigated under a multiaxial stress field. Changes in the aggregation structure of the films were investigated during the bulge deformation process using in situ small-angle X-ray scattering, wide-angle X-ray diffraction (WAXD) measurements, and polarized high-speed-camera observations. The films had a thickness of approximately 10 μm. The it PP films were fixed at the hole of a plate, then bulge deformation was applied using N₂ or He gas pressure, and stress-strain curves were then calculated from the applied pressure and bulge height. Yielding was observed in the stress-strain curves. Below the yield point, in situ WAXD measurements revealed that the crystal lattice expanded isotropically at the center, edge, and bottom of the bulge hole. Above the yield point, a craze started to form slightly near the center, and crazes formed in various directions with a further increase in strain, while the crystal lattice expanded uniaxially along the circumference at the edge and bottom. Crazes oriented in various directions merged and lost birefringence, indicating a change to the isotropic orientation. The different directions of the crazes indicated several directions of stress. In other words, even if multiaxial deformation is applied to a crystalline it PP film, the string-shaped crystalline polymer chain structure produces local anisotropic uniaxial stress.