Plastics,Rubber and Composites: Macromolecular Engineering

Thermal processing of poly(vinyl alcohol) (PVA) has been a big challenge worldwide because its melting point is very close to its decomposition temperature. Based on intermolecular complexation and plasticisation, an amido containing compound (Ac), which has a complementary structure to PVA, together with water, were adopted to improve thermal processing of PVA. The results show that water and Ac can control the supramolecular structure of PVA, confine its crystallisation, decrease its melting point, thus obtain the thermal processing window for PVA. In this way, melt spinning of PVA fibres, extrusion blowing of PVA films and extrusion blowing moulding of PVA containers are realised. Then PVA high performance fibres with tensile strength over 1·9 GPa, PVA blown films with good mechanical properties and transparency, and PVA containers with good gasoline barrier properties and thermal resistance are obtained. Compared with the traditional wet processing of PVA solution, the thermal processing technology adopted for modified PVA is much more simple, effective and cost saving. More encouragingly, the PVA container with excellent chemical resistance and physical properties will open a new application field for PVA.

The polymer blends of polyoxymethylene (POM) and gel acrylonitrile–butadiene elastomer (GNBE) with phenol formaldehyde resin (PFR) as the compatibiliser were prepared, and the structure and properties were studied. The results show that GNBE is an excellent toughening agent for POM. The blend POM/GNBE (80/20) with 6 phr PFR attains a notched Charpy impact strength of 21·6 kJ m⁻², an elongation at break of 133% and a tensile strength of 33·8 MPa. PFR is incorporated into GNBE and the hydroxyl groups in PFR form intermolecular hydrogen bonds with POM. Dynamic mechanical analysis studies show that POM and GNBE are partially miscible and the miscibility of the blends is improved by PFR. The results from TEM show that the size of the dispersed phase of the ternary blends decreased with increasing PFR content in the blends. A rubber band of GNBE dispersed phase and a complex wrapped structure in POM were observed in the POM/GNBE and POM/GNBE/PFR blends.

Polyoxymethylene (POM)/carbon nanotubes (CNTs) (2: 1 by weight) composite powders were prepared by a solid mechanochemical method with a self-designed pan type mill equipment. Photos of SEM and TEM show that the average size of composite powder is several micrometres, and the CNTs adhered to the surface of POM powder to form a special structure like silk cocoons. The composites were prepared by adding the mixed POM/CNTs powder to POM matrix. Three different processing methods were tried and the results confirm that the solid mechanochemical method is the most effective to reinforce the POM matrix. The good dispersion of CNTs in POM matrix is attained and the interface interaction between CNTs and POM is improved through the mechanochemical mixing. Compared with talc, calcium carbonate and carbon black, CNT is the most effective filler to reinforce POM due to its high aspect ratio. Differential scanning calorimeter analysis shows that in the presence of CNTs, the crystallisation temperature and enthalpy of POM are enhanced. Thermogravimetric analysis data suggest that the thermal stability of POM is also improved.

Some oxygen containing groups (mainly carbonyl group) are introduced onto the molecular chains of styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS) through ozone treatment, so as to improve the interface compatibility between PA6 and SEBS. With increasing ozonised SEBS content, toughness of the PA6/SEBS blend is increased. Compared with PA6/SEBS blend (80: 20), the impact strength of PA6/ozonised SEBS (80: 20) blend is increased from 21·5 to 68·7 kJ m⁻².

In this paper, high density polyethylene (HDPE)/montmorillonite nanocomposites (HDPECNs) were prepared via conventional and ultrasonic extrusion technology developed in the authors' laboratory. X-ray diffraction analysis, scanning and transmission electron microscopy results show that ultrasonic oscillations can effectively improve the dispersion of organic montmorillonite (OMMT) particles in HDPE matrix with some exfoliation of OMMT. The yield strength, elongation at break and Young's modulus of ultrasonicated HDPECNs with the ultrasonic intensity of 200 W are thus respectively improved by 11·1, 30·2 and 12·3% compared to those of conventional HDPECNs. The crystalline behaviour and spherulite morphology of HDPE in HDPECNs were also investigated by differential scanning calorimetry and polarising light microscopy. The results show that the OMMT particles and ultrasonic oscillations play important roles in the nucleation rate, crystallisation temperature and spherulite size of HDPE. Ultrasonic oscillations can improve the crystallinity and reduce the spherulite size of HDPE matrix in nanocomposites.

Effects of blending sequence on properties of a ternary polyolefin blend based on isotactic polypropylene (PP) have been studied. The ternary blend was composed of three components: PP, metallocene ethylene–octene copolymer (mPE) and high density polyethylene (HDPE), with PP as matrix, mPE and HDPE as toughened fillers. The ternary blends were prepared by melt mixing in a twin screw extruder under three different blending procedures: simultaneous mixing of the three components, premixing of mPE and HDPE followed by mixing with PP and premixing of PP and HDPE followed by mixing with mPE. It was found that Izod notched impact strength of the ternary blends prepared by simultaneous mixing was dramatically improved, and blends prepared by premixing of mPE and HDPE followed by mixing with PP had a higher modulus and a higher elongation at break than those of other ternary blends. The dependence of the microstructure on blending sequence was investigated.

Polypropylene/polyolefin elastomer (PP/POE) blends with and without β nucleating agent were prepared by injection moulding. Wide angle X-ray diffraction (WAXD) results are in agreement with differential scanning calorimetric (DSC) melting curves; both demonstrate the formation of the hexagonal β phase after adding β nucleating agent in PP/POE blends. The addition of β nucleating agent increases the toughness of PP and PP/POE blends but decreases their tensile strength. Brittle–ductile transition (BDT) occurs in PP/POE blends, but no obvious BDT point can be seen in β nucleated PP/POE blends. The toughening mechanism, morphology of the fractured surfaces after impact, was investigated by scanning electron microscope (SEM). From impact strength interparticle distance curves, a critical interparticle distance of ∼0·2 μm is seen in PP/POE blends, but no critical value is observed for β nucleated system, indicating better interaction between PP and POE, deduced by their good compatibility. The toughening and softening effect of β nucleating agent is also responsible.

How to improve the electrical properties of conductive polymer composite (CPC) such as lowering the percolation threshold and endowing the composite with unique properties is a most important research area in developing this kind of material. Various methods have been employed, among which changing the processing procedure of the material is the most simple. The present paper describes how the authors, by eliminating the mixing procedure before compression moulding, managed to fabricate a material with different percolation thresholds and much more stable volume resistivity temperature behaviours compared to that utilising the mixing procedure. Microstructures of these two materials were investigated. The authors found that the composite produced using the mixing procedure had much shorter conductive fibrils, while that produced without mixing had a hierarchical structure, in which long and well defined conductive fibrils composing the conductive sheet structure first and conductive sheet overlapped together to form the conductive network throughout the composite.

The effect of nanoCaCO₃ on crystallisation behaviour of linear low density polyethylene (LLDPE) was investigated through time resolved small angle light scattering (SALS). The results indicate that the spherulite size of LLDPE is influenced in the presence of nanoCaCO₃. In case the LLDPE and composites were crystallised at room temperature, the spherulite size of LLDPE composites is smaller than that of LLDPE. Also, the contents of the nanoCaCO₃ (20·0–30·0 wt-%) could influence the structure of spherulite. The spherulite size of LLDPE is also influenced by the crystallisation temperature. When the crystallisation temperature is increased to 85°C, the spherulite size of LLDPE is remarkably affected by the contents of nanoCaCO₃. At isothermal crystallisation temperature of 85°C, the crystallisation induction time of LLDPE is greatly shortened in the presence of nanoCaCO₃. Furthermore, there is an orientation fluctuation emerging in the early stage of crystallisation in LLDPE containing 2·0 wt-% nanoCaCO₃.

Hybrid films derived from two polymeric precursors of polyamic acid (HYBRID-PAA) and soluble polyimide (HYBRID-PI) were prepared via a sol–gel process from hydrolysed tetraethoxysilane (TEOS). The UV-vis and scanning electron microscopy results show that two sizes of silica particles were acquired from PAA, while a single size of silica particles was acquired from PI. This phenomenon was induced by the carboxyl group in PAA. The differential scanning calorimetry results show that the glass transition temperature (T _g) of the hybrid using PAA was 40°C higher than when using PI. The tensile strain stress test shows that the tensile strength and modulus of hybrid films from PAA are greater than that from PI; but the elongation at break of hybrid films from PAA is lower than that from PI. The dynamic mechanical analysis and thermal mechanical analysis tests further suggest that the thermal properties and mechanical properties are influenced by the morphology of hybrids.

A series of poly(p-phenylene-1,3,4-oxadiazoles) (PODs) were synthesised from terephthalic acid (TPA) and hydrazine sulphate in fuming sulphuric acid via a recently developed procedure, namely, one step with three stages. The influence of the reaction temperature and time, and molar ratio of SO₃/TPA on the cyclisation degree of POD was investigated. The structure of PODs was characterised by a Fourier transform infrared spectrophotometer, and the cyclisation degree was calculated based on the results of elemental analysis. The stability and fluidity of POD solutions with different cyclisation degrees were determined by viscometry. The filaments of PODs were formed through wet spinning, in which the POD solutions were directly extruded into a coagulating bath containing 40% sulphuric acid solution. The thermal resistance and structure of POD fibres were studied by thermogravimetric analysis, SEM and wide angle X-ray diffraction. The relationship between the fibre's properties and the cyclisation degree was discussed. Results show that the POD solutions with high cyclisation degree are stable and spinnable. The thermal, mechanical and chemical properties of fibres depend greatly on the cyclisation degree of POD fibre and post-treatment conditions. The higher the cyclisation degree of POD fibre, the better the properties, except for those fibres which have undergone extensive heat-treatment. The resulting POD fibres have good thermal stability and moisture regain, as well as proper mechanical properties. These fibers can be used as heat resistant filtering fabrics, and protective working clothes for firemen, metallurgists and welders.

A series of alkyl ammonium/montmorillonite (MMT) organoclays were selected and melt blended with polyoxymethylene (POM) to explore the effect of MMT on the thermostability and mechanical properties of POM. The effects of the nature of the surfactants used in MMT modification on the intercalation of POM chains within the silicate galleries, the interfacial compatibility of POM/MMT and the thermostability of the composites were studied. The POM/MMT composites were prepared via melt, solution, solid state pan milling and in situ intercalative polymerisation blending method respectively, and the effects of preparation methods on the dispersion and exfoliation of MMT in POM matrix were measured by the wide angle X-ray scattering analysis. The thermal stabilisation effect of MMT on POM was studied by the isothermal weight loss analysis, thermogravimetric analysis (TGA) and formaldehyde emission amount measurement (FEA), which showed that a proper type and content of surfactant modified MMT may endow POM with improved thermostability. The crystallisation behaviour of POM/MMT composite was studied by the methods of polarised light microscopy (PLM), isothermal and non-isothermal crystallisation, which showed that a proper type and content of MMT had remarkable nucleation effect on POM and can improve the mechanical properties of POM efficiently.

The poly(dimethylsiloxane)–titanium dioxide (PDMS–TiO₂) composites were prepared by emulsion polymerisation of octamethylcyloteterasiloxane (D₄) in the presence of TiO₂ particles modified by [γ-(methacryloxy)-propyl] trimethoxysilane (γ-MPS). The structure of the prepared PDMS–TiO₂ composites was characterised by fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The results show that PDMS is grafted onto the surface of TiO₂ particles via γ-MPS. The photocatalytic activity of PDMS–TiO₂ composites was evaluated by decomposition of methyl orange (MeO). The result indicates that PDMS–TiO₂ composite is one kind of efficient catalyst for MeO decomposition and the decomposition rate constant of MeO for PDMS–TiO₂ composite is ∼3 times of that for TiO₂. UV-vis diffuse reflectance spectra measurements show that the absorbance of PDMS–TiO₂ composites is higher than that of TiO₂ in the visible light range.

A kind of temperature sensitive polymers of acrylamide (AM) and 3-isopropenyl-α, α-dimethylbenzyl urethane (macromer) were synthesised by free radical aqueous solution copolymerisation. Their molecular structures were verified by ¹H NMR and fourier transform infrared (FTIR) spectroscopy. Some factors affecting synthesis, such as macromer content, initiator concentration, reaction temperature as well as solution behaviours of these polymers were studied. The results show that these factors have significant effect on the performance of the products, the optimum reaction conditions are 1·8 mol-% macromer, 0·4 wt-% initiator and 35°C. The copolymer solutions exhibit good thermothickening behaviour. Even at 0·15 wt-% polymer solution, a typical thermothickening behaviour can be seen. The higher the polymer concentration, the more prominent the thermothickening behaviour of polymer solution. The polymer solutions show shear thickening behaviour.

The devulcanisation of natural rubber (NR) vulcanisate was carried out with the self-designed pan mill type mechanochemical reactor that can exert fairly strong shearing force on the milled materials. The experimental results indicate that gel fraction of the devulcanised NR is substantially reduced, and the reduction of molecular weight of the sol part of devulcanised NR is not significant. The mechanical properties of the revulcanised NR increase with increasing milling cycle. After mechanochemical milled 30 cycles, the tensile strength increased to 7·1 MPa, which is about 60% of that of the virgin NR vulcanisate. Elongation at break as high as 973·0% was obtained, which is the same as that of the virgin NR vulcanisate. Solid state mechanochemical milling is a simple, low cost method for the devulcanisation of cross-linked rubber vulcanisates at ambient temperature without the use of any chemicals and is feasible to be industrialised.