Improving thermal stability and mechanical performance of polypropylene/polyurethane blend prepared by radiation-based techniques

Optimization of the Physical Properties of HDPE/PU Blends through Improved Compatibility and Electron Beam Crosslinking

Polymer blending is a method in which polymers with different properties are mixed so that each advantage appears in one polymer blend. Improved thermal and mechanical properties of blends can be prepared by blending with high-density polyethylene (HDPE) of a non-polar polymer and polyurethane (PU) of a polar polymer. However, a compatibilizer is required because it has the disadvantage that blending has low miscibility due to the different phases. In this study, HDPE/PU blends with new and excellent physical properties were developed through optimal composition with improved compatibility between the HDPE and PU. In addition, the effects of improving the physical properties through electron-beam crosslinking were confirmed. In general, a crosslinking structure of HDPE is formed by electron beam irradiation to increase its thermal stability and strength, but its elongation is rapidly decreased. In particular, the elongation of HDPE irradiated at 100 kGy was about 110%, which was decreased about five times compared to unirradiated HDPE (510%). However, the HDPE/PU blend with improved compatibility (PU 30) showed an elongation of about 450% while maintaining excellent strength (22.5 MPa), which was increased by about four times compared to the HDPE irradiated at 100 kGy. In particular, the thermal stability of PU 30 irradiated at 100 kGy at a high temperature (180 °C) was improved more than six times compared to the HDPE. Therefore, it is possible to develop HDPE/PU blends with new and excellent physical properties by improving compatibility and using electron beam crosslinking technology.

Radiation-Based Crosslinking Technique for Enhanced Thermal and Mechanical Properties of HDPE/EVA/PU Blends

Crosslinking of polyolefin-based polymers can improve their thermal and mechanical properties, which can then be used in various applications. Radiation-induced crosslinking can be done easily and usefully by irradiation without a crosslinking agent. In addition, polymer blending can improve thermal and mechanical properties, and chemical resistance, compared to conventional single polymers. In this study, high-density polyethylene (HDPE)/ethylene vinyl acetate (EVA)/polyurethane (PU) blends were prepared by radiation crosslinking to improve the thermal and mechanical properties of HDPE. This is because HDPE, a polyolefin-based polymer, has the weaknesses of low thermal resistance and flexibility, even though it has good mechanical strength and machinability. In contrast, EVA has good flexibility and PU has excellent thermal properties and wear resistance. The morphology and mechanical properties (e.g., tensile and flexure strength) were characterized using scanning electron microscopy (SEM) and a universal testing machine (UTM). The gel fraction, thermal shrinkage, and abrasion resistance of samples were confirmed. In particular, after storing at 180 °C for 1 h, the crosslinked HDPE-PU-EVA blends exhibited ~4-times better thermal stability compared to non-crosslinked HDPE. When subjected to a radiation dose of 100 kGy, the strength of HDPE increased, but the elongation sharply decreased (80%). On the other hand, the strength of the HDPE-PU-EVA blends was very similar to that of HDPE, and the elongation was more than 3-times better (320%). Finally, the abrasion resistance of crosslinked HDPE-PU-EVA was ~9-times better than the crosslinked HDPE. Therefore, this technology can be applied to various polymer products requiring high heat resistance and flexibility, such as electric cables and industrial pipes.

Extraction of the Polyurethane Layer in Textile Composites for Textronics Applications Using Optical Coherence Tomography

This article presents a new method for the extraction and measurement of the polyurethane layer of Cordura textile composites using optical coherence tomography. The knowledge of coating layer properties in these composites is very important, as it affects mechanical parameters such as stiffness and bending rigidity. Unlike microscopic measurements, which require cross-section samples of the material, the proposed approach is non-invasive. The method is based on detecting the top and bottom boundaries of the polyurethane layer in Optical Coherence Tomography (OCT) images using image processing methods, namely edge enhancement filtering, thresholding and spline smoothing. The cover layer measurement results obtained from a three-dimensional OCT image of the composite fabric are presented as the thickness maps. The average values of the layer thicknesses measured with the OCT method for four types of Cordura showed a high correlation with the results obtained from microscopic measurements (Pearson correlation coefficient r = 0.9844 ), which confirms the accuracy of the OCT method.