Plastics,Rubber and Composites: Macromolecular Engineering

Maleic anhydride (MA) grafted styrene ethylene butadiene styrene copolymer (SEBS-g-MA) and styrene MA copolymer (SMA) were used to compatibilise and toughen poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 (PPO/PA6) blend. The mechanical properties, morphology and rheological behaviour of PPO/PA6/SEBS-g-MA/SMA blends with different SEBS-g-MA and SMA content were studied. SEBS-g-MA was an effective impact modifier for PPO/PA6/SMA blends, and the notched Izod impact strength reached 143 J m⁻¹ at the SEBS-g-MA content of 25 parts per hundred rubber (phr). The morphology observation showed that the dispersed phase of PPO/PA6 blends was more uniform, and its size became smaller after the addition of SMA, indicating an effective compatibilisation. Furthermore, the elongation at break of the blend reached 86·3% at the SMA content of 5 phr. In conclusion, PPO/PA6/SEBS-g-MA/SMA blends with better mechanical properties could be obtained at the SEBS-g-MA content of 20–25 phr and SMA content of 2–5 phr.

To understand the effects of thermal gradient field with phase change on the crystal morphologies of high density polyethylene (HDPE) during gas assisted injection moulding (GAIM) process, the combination of the simulation of the temperature field via an enthalpy transformation method and the hierarchical structures and the crystalline morphology of HDPE were investigated in this work. The GAIM parts of HDPE 6098 can be grouped into four layers in the direction of thickness: skin layer, subskin layer, intermediate layer and core layer. Besides, the cooling logarithmic curves were adopted in this experiment, and it is found that they can clearly display the phase change plateaus even at the skin layer zone.

The morphological and structural evolution of quenched high density polyethylene specimens subjected to different strains during the heating process was explored via synchrotron small-angle X-ray scattering technique. On the basis of one-dimensional scattering intensity distribution profile analysis, a general scheme for the melting of polyethylene was proposed that surface melting occurs below the crystallisation temperature, followed by melting and recrystallisation and/or lamellar thickening process via sequential melting and stack melting at the ultimate stages of melting. It was shown that in the case of undeformed specimen, the crystallisation process has finished at the temperature of ∼90°C during quenching, while the crystallisation temperature is equivalent to 70°C for the highly oriented sample, which was attributed to the thermal effects in the necked region due to high strain rate. A qualitative argument that the isotropic material possesses a wide distribution of lamellar (or amorphous domain) thicknesses with respect to the highly oriented one can be made in terms of the temperature dependent one-dimensional correlation function. In addition, it could be evidenced that moderate deformation ratio does not affect the intrinsic property of existing stacks of lamellar crystals by a direct comparison of the evolution of structural parameters of their lamellar structure during heating.

Thermoplastic polyurethane (TPU)/multiwalled carbon nanotube (MWNT) composites were prepared through mixing and extrusion process in a minimixer equipped with a single screw plus twin shaft paddles. In order to improve the dispersion of MWNT and the compatibility between MWNT and polyurethane, the MWNT were functionalised with polytetramethylene ether glycol (PTMEG) through a grafting process to get the MWNT-g-PTMEG. The relationship between the structure and properties of the TPU/MWNT composites was examined. The results showed that MWNT-g-PTMEG can be uniformly dispersed in the TPU matrix, and the tensile strength and elongation at break were both improved. For 1 wt-%MWNT-g-PTMEG/TPU composites, the tensile strength and elongation a break were enhanced to ∼41 MPa and 568% respectively, while for pristine TPU, they were ∼34 MPa and 508% respectively. Dynamic mechanical analysis showed that the storage modulus at room temperature increased, and the maximum tan δ decreased with increasing MWNT-g-PTMEG contents. The simultaneous small and wide angle X-ray scattering measurements showed that with the incorporation of MWNT-g-PTMEG, the degree of crystallinity, interdomain distance, hard domain thickness as well as the degree of microphase separation increased. It appears that the functionalised MWNT-g-PTMEG promotes the formation of the ordered lamellar structure of polyurethane hard segments.

Poly(vinyl alcohol) (PVA) is a polyhydroxyl polymer with many excellent properties and wide uses. However, its applications are based on and limited in wet process due to its very close melting point and decomposition temperature. In this paper, based on the thermal processing technology of PVA developed in the State Key Laboratory of Polymer Materials Engineering through molecular complexation and plasticisation and by cooperating with the Polymer IRC Bradford site, small scale injection moulding of modified PVA has been realised on the FANUC 5t injection moulding machine. The effect of the modifier content on the melt behaviour, melt crystallisation behaviour and rheological properties of PVA, and the effect of processing conditions on mechanical properties of PVA injection samples were studied. The transparent PVA injection samples with uniform structure and 42 MPa tensile strength were obtained with proper modifier content and at optimum processing conditions. This is a convenient way to produce high performance PVA three-dimensional products.

The nanosized ZnO particles were prepared and filled into bisphenol A polycarbonate by melt blending process. The thermal property and processing stability as well as the optical performance of the nanocomposites were investigated. The results indicated that the thermal degradation was accelerated by adding nanosized ZnO into the polycarbonate, the processing stability and performance of the material became deteriorated during the melt blending process and its eventual usage. A strategy was developed to overcome this shortage: the nanosized ZnO was covered by an inert amorphous SiO₂ shell to protect the polymer chains from direct contact with the active surface of ZnO. Both the thermal stability and processing stability of the polymer nanocomposites were improved after adding the encapsulated ZnO particles. Besides, the transparency of the nanocomposites was also improved by adjusting the component ratio of the core–shell particle according to a refractive index law without losing the UV shielding efficiency.

A series of isotactic polypropylene (iPP)/calcium carbonate (CaCO₃) composites are prepared by melt blending, and the crystallisation behaviours of these composites are investigated by differential scanning calorimetry (DSC). The results show that the crystallisation exotherms displayed double peaks as the concentration of CaCO₃ reaches a critical value of typically ∼8 wt-% for nano-CaCO₃ and ∼20 wt-% for micron-CaCO₃. With increasing content of CaCO₃, the intensity of the higher temperature crystallisation peak increases, while that of the lower one decreases. Modifying the surface of CaCO₃ with stearic acid leads to the increase in the critical concentration to trigger double crystallisation peaks, which is 50 wt-% for nano-CaCO₃ filled iPP. The results of isothermal crystallisation, transmission electron microscopy (TEM) and polarised light optical microscope (POM) experiments indicate that the different nucleating abilities of CaCO₃ composites are mainly responsible for the occurrence of the double crystallisation peaks in the composites.