Impact of Thermal Properties on Crystalline Structure, Polymorphism and Morphology of Polymer Matrices in Composites

Morphological analysis at different levels is fundamental to understand properties of materials, as these latter are dictated not only by the chemical composition but also by the shape. Solid structures arise from a balance between thermodynamic and kinetic factors, which, especially for polymer composites, depend also on interactions amongst components. In particular, morphology is strongly affected by the heat transfer pattern during crystallization and by the difference in thermal behavior between polymer matrix and filler. Polymers show a spherulitic structure, arising from the start of crystallization in several points of the liquid phase. Within a general rounded shape, spherulites show variability in growth patterns, morphology, and geometry of boundaries. The appearance and the number of spherulites, as well as their growth mechanism, may vary not only in dependence of the chemical composition and the crystalline structures but also, for a same polymer, in consequence of experimental conditions and incorporation of fillers. This article reviews the crystallization process of polymer matrices in the framework of crystal growth and heat transport theories, and explains microstructural differences between composites and neat matrices on the basis of the differences in thermal capacity and conductivity between polymers and additives.

The Effect of Top Surface Lubrication on the Friction Stir Welding of Polycarbonate Sheets

In this work, top surface lubrication during friction stir welding of polycarbonate sheets was applied. A homogenous layer of Paraffin wax has been placed on the top surface of the joint area with a width that ensures to cover the shoulder diameter. Then FSW was applied using conventional FSW tool with rotating pin and shoulder at different FSW parameters (Rotation speeds of 1 000, 1500, 2 000 min–1 and welding speeds of 25, 50, 75,100 mm/min). The main objective of using the wax is to act as a lubricant that reduces the friction between the shoulder and the polycarbonate surface. The joints produced were investigated in terms of surface quality, internal defects, and mechanical properties. During FSW the wax is melted and played as lubricant between the tool shoulder and the polycarbonate surface and resulted in defect-free surface with no thickness reduction of the original plate. The transverse cross-section showed defect-free joints for the majority of the FSW parameters investigated. Tensile testing results showed a reduction of the tensile strength after FSW, and an enhancement in the tensile strength with the increase of welding speed or rotation speed. The fracture occurs at the joint zone and the fracture surface investigation using SEM showed the existence of spherulitic structure in the weld joint.

Tribotechnical Properties of HA Nanocomposite Based on UHMWPE under Dry Sliding and Lubrication

The tribotechnical properties of hydroxyapatite (HA) nanocomposite based on ultra-high molecular weight polyethylene (UHMWPE) under dry sliding and lubrication of distilled water and plasma blood was investigated with block-on-ring. It was shown that modification of UHMWPE by HA nanoparticles within range of 0.1–0.5 wt.% results in decrease of wear intensity at dry sliding up to 3 times. The under lubrication, wear intensity of pure UHMWPE and nanocomposite are deceased up to 50–70% as compared with under dry sliding. Permolecular structure of pure UHMWPE and nanocomposite are spherulitic structure, which nanoparticle does not alter the nature of the permolecular structure, and homogeneously dispersed in the UHMWPE matrix.

Tribotechnical Properties of UHMWPE Based Composite Filled with HA Microparticles under Dry Sliding and Lubrication

The tribotechnical properties of ultra-high molecular weight polyethylene (UHMWPE) based composite filled with hydroxyapatite (HA) microparticles under dry sliding and lubrication of distilled water and plasma blood wear investigated with block-on-ring. It was shown that modification of UHMWPE by HA microparticles of 20 wt.% results in decrease of wear intensity at dry sliding up to 4 times. The under lubrication, wear intensity of pure UHMWPE and microcomposite are deceased up to 50–70% as compared with under dry sliding. Permolecular structure of pure UHMWPE and microcomposite are spherulitic structure and the HA microparticles were dispersed in the UHMWPE matrix.

Crystallization Behavior and Crystal Morphology of PP/POEg Blends

Polypropylene (PP)/Maleic anhydride grafted poly (ethylene-octene) (POEg) were prepared by melt blending method. The crystallization behavior and crystal morphology were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarzing optical microscope (POM). Differential scanning colorimetry (DSC) experiments showed that the melting point and crystallization point decreased when POEg added to the blend. XRD results show that the POEg not change the crystal structure in the blends but only decrease the intensity of the diffraction peak. The spherulitic structure could also observed when added POEg to the matix of PP, but the shape of the spherulites distorted.

Investigations of polycaprolactone/gelatin blends in terms of their miscibility

Synthetic and natural polymers blends represent a new brand of materials with application in wound healing, scaffolds or drug delivery systems. Polycaprolactone/gelatin (PCL/Gt) blends were analyzed in terms of their miscibility. The PCL structure was investigated as a function of Gt content. Changes in the PCL spherulitic structure with Gt content were investigated by a polarizing-interference microscope. The analysis of the glass transition temperature (Tg) of both components as a function of PCL/Gt ratio by differential scanning calorimetry indicates that the system of polycaprolactone/gelatin belongs to a type of s.c. compatible system, being intermediate between miscible and immiscible systems. There is possibility of very limited miscibility of both components. Supplementary wide angle X-ray scattering results are presented.