The degradable polymers polylactide (PLA) and polylactide-co-glycolide (PLGA) have found widespread use in modern medical practice. However, their slow degradation rates and tendency to lose strength before mass have caused problems. The aim of this study was to ascertain whether treatment with e-beam radiation could address these problems. Samples of PLA and PLGA were manufactured and placed in layered stacks, 8.1 mm deep, before exposure to 50 kGy of e-beam radiation from a 1.5 MeV accelerator. Gel permeation chromatography testing showed that the molecular weight of both materials was depth-dependent following irradiation, with samples nearest to the treated surface showing a reduced molecular weight. Samples deeper than 5.4 mm were unaffected. Computer modeling of the transmission of a 1.5 MeV e-beam in these materials corresponded well with these findings. An accelerated mass-loss study of the treated materials found that the samples nearest the irradiated surface initiated mass loss earlier, and at later stages showed an increased percentage mass loss. It was concluded that e-beam radiation could modify the degradation of bioabsorbable polymers to potentially improve their performance in medical devices, specifically for improved orthopedic fixation.

In this paper, a study of the relationship between the impact performance of rotationally molded polyethylenes and their dynamic mechanical properties is carried out. A wide range of conventional linear low density polyethylene powders and met‐allocene catalyzed linear low density polyethylene powders were rotationally molded and tested. Instrumented falling weight impact tests were carried out over a temperature range of −60°C to 20°C. Dynamic Mechanical Thermal Analysis (DMTA) tests were also carried out between −100°C and 90°C, at a frequency of 100 Hz. Comparisons between the impact performance of metallocene catalyzed LLDPEs and Ziegler‐Natta LLDPEs are made. The transitions evident in the DMTA results are related to changes in impact performance with temperature. The beta transition is found to fall in the transition region between high impact performance at low temperatures and lower impact performance at ambient temperatures.

This paper presents work from an ongoing study into the use of post-consumer waste polymer in the rotational moulding process. Raw plastic recyclate, predominantly consisting of polyethylene, was processed into polymer powders containing an additive package suitable for rotational moulding, with and without the addition of a compatibiliser. Rheological studies on the materials showed very high viscosities at low shear rates in comparison with materials typically used in rotational moulding, which has significant implications for melt flow and bubble removal during the process. It was possible to mould the materials successfully, but poor surface finishes were achieved. Impact strength was drastically lower for recyclate mouldings compared with virgin material. Tensile strength of the recyclate mouldings was reduced compared to virgin polyethylene, but results indicated that optimising the processing conditions could lead to improvements. This work gives some baseline indicators to inform further planned work on optimising processing conditions and identifying viable material compositions.

The present paper describes trials that were carried out on a conventional and a metallocene linear low density polyethylene to determine the effect of bubble content on the impact performance of rotationally moulded parts. Internal mould pressurisation was applied at different levels and at different internal air temperatures during the moulding cycle. The quantity of bubbles in the different mouldings was determined and related to impact performance at room temperature and at 240uC. Variations in dynamic mechanical properties were also highlighted.

The objective of this paper is to provide a better understanding of how thermal relaxations in linear low density polyethylenes are related to the crack initiation energy of rotomoulded parts. Trials were carried out on two Ziegler -Natta catalysed linear low density polyethylenes (LLDPE) and two metallocene catalysed linear low-density polyethylenes (mLLDPE). Instrumented impact tests and dynamic mechanical thermal analysis (DMTA) were carried out on each material at a wide range of temperatures. The frequency of impact at each test temperature was determined, and the DMTA results were shifted to a corresponding frequency. A correlation can be seen between changes in loss modulus and crack initiation energy with temperature. When comparing the crack initiation energy of the samples and the tan d values, it can be seen that the b transition affects the way in which the polymer behaves under impact. A method for predicting impact performance over a wide temperature range is proposed.