Stress-strain behavior of four types of polyethylene (PE), i.e. low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE) and high-density polyethylene (HDPE), under a wide strain rate ranging from 0.001 to 1000 s−1, and the crystalline structures of corresponding fractured PEs were investigated. Results demonstrated that when the strain rate was less than 1 s−1, PE exhibited ductile fracture with a rougher section. While at strain rates larger than 1 s−1, the damage was manifested as brittle fracture with a smooth fracture surface. For all PE specimens, the yield strength increased with strain rate, but the increasing dependency of yield stress on strain rate was diverse in various strain rate ranges. Under the same strain rate, due to the largest molecular weight and lowest branching degree, HDPE showed the highest values in yield strength, crystallinity, crystal orientation degree, and crystallite size. At the appropriate stain rate, i.e. 10 s−1, HDPE with less branched structure is more likely to obtain higher crystallinity and molecular chain orientation degree.

Abstract High density polyethylene (HDPE) was toughened by linear low density polyethylene (LLDPE) and polypropylene (PP) to prepare HDPE film, and the melt index, haze, mechanical properties and morphology structure of the modified HDPE film were studied. The results showed that the toughening effect of the 10%PP/30%LLDPE/60%HDPE composition was the best; the haze was reduced 6%, dart impact strength and elongation at break were increased 27.3% and 47%, respectively. The blend of 10%PP/30%LLDPE/60%HDPE had good compatibility, and the toughness of modified HDPE film was improved.

ABSTRACT Polyethylene-based modification for asphalt is more and more widely used in paving engineering to deal with growing rutting distress on road pavement. The internal structure of polyethylene (PE) and the resulting asphalt are of interest due to their great influences on performance of pavement. This study investigated the correlation between polyethylene structure and asphalt performance. The polyethylene considered in this paper incorporates high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). The influence of various PEs on rheological properties of asphalt was investigated by SHRP (Strategic Highway Research Program) method. Compatibility was also evaluated by rheological criterion and microscopic characterisation. The results indicated that modulus, G*/sinδ and viscosity of MDPE modified asphalt are largest among studied samples and it is a good choice for asphalt modification from the perspective of rutting resistance. LLDPE modified asphalt showed the preferable low temperature performance and LDPE is most compatible with asphalt. Higher branched degree of PE improves the low temperature performance of asphalt, but it reduces high temperature performance. A reduction in MFI (melt flow index) facilitates improvement of rutting resistance performance. Unfortunately, low MFI makes PE difficult to be dispersed and leads to poor compatibility with asphalt.

To prepare high-density polyethylene (HDPE) films with excellent mechanical properties and lower haze, HDPE was modified by using linear low-density polyethylene (LLDPE) and polypropylene (PP), and their characterizations were performed by melt index, light transmittance/haze, dart impact and elongation at break, infrared (IR) spectra, scanning electron microscopy image and IR image analyses. The results showed that the modifying effect of the 10% PP/30% LLDPE/60% HDPE composition was the best; the haze was reduced 6% and the translucency, dart impact strength, elongation at break and tensile strength were increased 1, 27.3, 29.4 and 1.0%, respectively. The blend of 10% PP/30% LLDPE/60% HDPE had good compatibility, and PP, LLDPE and HDPE were only the physical entanglement, and no chemical reaction, the modified HDPE films can partly replace polyvinyl chloride and LLDPE films.

This study aimed an experimental data about the effect of physical properties of samples on the mechanical characteristics of high-density polyethylene (HDPE) used for the manufacture of preinsulated pipes for heating networks. The main waterproofing insulation material in the construction of preinsulated pipelines for heating networks is polyethylene. Outer outer casing of preinsulated pipes made of high density polyethylene (HDPE) are used as a waterproofing insulation of polyurethane foam of steel pipes manufactured in the factory. The sufficient resistances to cracking and mechanical stress, resistance to ultraviolet radiation, high density, high strength, low aging are main properties of HDPE. The study of HDPE of different manufacturers is relevant because of the aging of preinsulated pipelines with HDPE outer casing. In this study are tested physical characteristics of HDPE as a melt flow rate, density at 23°C, water content of PE80, PE100 pipe polyethylene of different world manufacturers. The best samples of HDPE and the effects of various aging factors on the properties of polyethylene are presented.

Yellow and dark mealworms (Tenebrio molitor and Tenebrio obscurus) biodegrade commercial polyethylene (PE) materials at a high rate. We examined the impact of physical and chemical properties on biodegradation using high purity microplastics (MPs). These included high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE), all with different weight average molecular weights (Mw) and different crystallinity degrees in T. molitor and T. obscurus larvae. The biodegradation extent in the two mealworms was similar but strongly depended on the polymer type in sequence, since LDPE > LLDPE> HDPE (with respective Mw of 222.5, 110.5 and 182 kDa). When LDPE MPs with Mw of 0.84, 6.4 and 106.8 kDa and HDPE with Mw of 52, 105 and 132.7 kDa were tested, the PE MPs with lower Mw showed a greater extent of depolymerization. The results of dominance analysis indicated that less branching structure and higher crystallinity degree negatively impacted depolymerization and biodegradation. Py-GC/MS analysis confirmed the breaking of the macromolecule backbone as well as the formation of oxidized functional groups after all the tested PE materials passed through the mealworm intestine. The results demonstrated that molecular weight, PE type, branching, and crystallinity degree significantly affect the biodegradation capability of PE by the mealworms, and possibly by other biological systems as well.

In this study, four kinds of specimens of PE(polyethylene)-based insulating materials were prepared for selecting the optimum insulation materials in a wet environment. The specimens were tested by various methods, the anti tracking test, the transmittance test in the water vapor transmittance(WVT) and the abrasion resistive test, etc. The HDPE(high-density polyethylene) specimen was showed excellent property in the tracking resistance test and the lowest transmittance in water vapor transmittance test. In the abrasion resistive test, the LLDPE(linear low-density polyethylene) and MDPE(medium-density Polyethylene) were showed excellent mechanical properties. The value of cut-through resistance for MDPE and HDPE were superior to that for LLDPE and LDPE(low-density polyethylene).

In this work, the effect of temperature and crystallinity on the thermal conductivity was investigated in a series of polyethylenes (PEs) with different crystallinities including high-density polyethylene (HDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE). It was found that the applied ambient temperature has a significant effect on the thermal conductivity. At −20~100 °C, the thermal conductivity of PE showed a linearly decline with the increase of temperature. The thermal properties of a series of PE samples were also investigated by differential scanning calorimeter. The results showed that the higher the crystallinity, the higher the thermal conductivity of polyethylene. However, above the melting point, thermal conductivity of all PE samples tended to be the same, with a value of about 0.21 W/m·K. Based on the crystallinity and temperature, an empirical formula was proposed to predict the thermal conductivity of PEs with an error within 3%, which was also consistent with the results of other reported thermal conductivity of PEs. This work can guide the design of thermally conductive polymers in the future.

In order to study the effects of the crystallinity of polyethylene with different densities on breakdown strength and conductance properties, this paper mainly tests the X-ray diffraction (XRD), different scanning calorimeter (DSC), direct current (DC) breakdown and conductance properties of low-density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), and high-density polyethylene (HDPE), and further analyzes the experimental results separately. The results show that an increase in the density of polyethylene leads to the continuous improvement of crystallinity, and an increase in crystallinity causes a significant decrease in the conduction current at the same field strength. The field strength corresponding to the two turning points in the conductance characteristic curve increases simultaneously.

Mechanical properties of blend of high density polyethylene (HDPE) and low density polyethylene (LDPE) have been investigated. Four different HDPE/LDPE blends with various ratio (80/20,60/40,40/60, and 20/80) were prepared by melt-mixing technique using mini-twin-extruder at 200 ᵒC and 90rpm. Characterization tests including tensile and impact strength tests as well as hardness have been performed in order to better understand the behavior of these blends. Information on ductility and toughness were obtained from the stress-strain curves of HDPE/LDPE blends. Mechanical properties were varied according to LDPE content. Blends-rich with LDPE showed to have lower strength and hardness and higher elongation, impact strength, ductility and toughness than blends-rich with HDPE. Blend with the composition (HDPE (40)/LDPE (60)) showed comparatively better overall mechanical properties.