The effect of thermoplastic starch on the properties of HDPE/TPS blends during UV-accelerated aging

Crystallinity of Amphiphilic PE-b-PEG Copolymers

The crystallinity and the growth rate of crystalline structures of polyethylene glycol and polyethylene blocks in polyethylene-b-polyethylene glycol diblock copolymers (PE-b-PEG) were evaluated and compared to polyethylene and polyethylene glycol homopolymers. Melting and crystallization behaviours of PE-b-PEG copolymers with different molecular weights and compositions are investigated by differential scanning calorimetry (DSC). The polyethylene/polyethylene glycol block ratio of the copolymers varies from 17/83 to 77/23 (weight/weight). The influence of the composition of PE-b-PEG copolymer on the ability of each block to crystallize has been determined. Thermal transition data are correlated with optical polarized microscopy, used to investigate the morphology and growth rate of crystals. The results show that the crystallization of the polyethylene block is closer to the polyethylene homopolymer when the copolymer contains more than 50 wt. % of polyethylene in the copolymer. For PE-b-PEG copolymers containing more than 50 wt. % of polyethylene glycol, the polyethylene glycol block morphology is almost similar to the PEG homopolymer. An important hindrance of each block on the crystallization growth rate of the other block has been revealed.

Degradation Monitoring of HDPE Material in CO2-Saturated NaCl Environment through Electrochemical Impedance Spectroscopy Technique

Extensive damage due to saturated seawater and CO2 exposure under high temperature and pressure in high-density polyethylene (HDPE) has been studied by Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Field Emission Scanning Electron Microscope (FESEM), and Electrochemical Impedance Spectroscopy (EIS). The degradation of square-shaped HDPE samples having 1 mm thickness was investigated at 70 bars with 60, 75, and 90 °C separately for three weeks in an autoclave chamber. A clear indication of aging was observed in terms of chain scission by the formation of the methyl group (1262 cm-1), and the appearance of degradation products, including the alcohol and hydroxyl groups. The decline in glass transition temperature (Tg), melting point (Tm), and crystallinity (Xc) result from branching and formation of degradation products in the aged samples. TGA results reveal that the degradation shifts the characteristic temperatures (T5% and T10%) to lower values compared to virgin HDPE. FESEM images show clear surface cracks and rough patches after 3 weeks. The Xc value increased due to chain mobility at higher temperatures (90 °C). The impedance is relatively high 1011 ohms.cm-2 for a virgin sample, but it drops down to 109 and 106 after degradation. Impedance and dielectric loss were correlated, and the significance of dielectric loss was observed at lower frequencies. These characterizations will contribute to more efficient and detailed evaluation criteria for degradation monitoring.

Starch-Based Fishing Composite Fiber and Its Degradation Behavior

The starch-based fishing composite fibers were prepared by one-step reactive extrusion and melt spinning. The effects of starch contents on the microstructural, thermal, dynamic mechanical, and mechanical properties of starch-based composite fibers were studied. And the degradation behaviors in soil of the fibers were also investigated. The compatibility between starch and HDPE is improved significantly by grafting maleic anhydride (MA) using one-step reactive blending extrusion. As the starch content increased, the melting temperature and the crystallinity of the fibers gradually decreased due to fluffy internal structures. Dynamic mechanical analysis showed that the transition peak α in the high-temperature region was gradually weakened and narrowed with increasing starch content; moreover, a shoulder appeared on the low-temperature side of the α peak was assigned to the β-relaxation related to starch phase. In addition, the mechanical results showed the significant decrease in the breaking strength and increase in the elongation at break of the starch-based composite fibers as the starch content increased. After degradation in soil for 5 months, the surface of the composite fibers had been deteriorated, while flocculent layers were observed and a large number of microfibers appeared. And the weight loss rate of the starch-based composite fibers (5.2~34.8%) significantly increased with increasing starch content (50~90 wt%).

The promiscuous activity of alpha-amylase in biodegradation of low-density polyethylene in a polymer-starch blend

Blending polyolefins with certain types of natural polymers like starch can be beneficial to their biodegradation. The impact of alpha-amylase on the biodegradation of low-density polyethylene (LDPE)-starch blend samples in an aqueous solution was investigated through characterizing their physical, mechanical and chemical properties. Results indicated that the weight and tensile strength of the enzyme treated samples were reduced by 48% and 87% respectively. Moreover, differential scanning calorimetry (DSC) showed an increase in fusion enthalpy of degraded samples which means that the crystallinity has been increased. The biodegradation of LLDPE appeared in Fourier-transform infrared spectroscopy (FT-IR) through the reduction in the intensity of the related peaks. This observation was supported by energy dispersive x-ray spectroscopy (EDXS) analysis where decreasing the percentage of carbon atoms in the treated blend was obtained. Likewise, the gel permeation chromatography (GPC) results pointed to a significant reduction in both the molecular weight and viscosity of LDPE more than 70% and 60% respectively. Furthermore, thermal gravimetric analysis (TGA) affirmed the function of amylase in degradation of the blend. On the basis of the obtained results, it can be claimed that the main backbone of the polymer, as well as the side branches, have been scissored by the enzyme activity. In other words, alpha-amylase has a promiscuous cometabolic effect on biodegradation of LDPE in polymer-starch blends.

Thermoplastic starch–polyethylene blends homogenised using deep eutectic solvents

Deep eutectic solvents are shown to be effective modifiers to enable polyethylene to be blended with starch to make a plastic with which can be more easily degraded.