All issues / Volume 7 (2013) / Issue 2 (February)
This is an editorial article. It has no abstract.
This paper focuses on the reinforcing of Poly(lactic acid) with chopped basalt fibres by using silane treated and untreated basalt fibres. Composite materials with 5–10–15–20–30–40 wt% basalt fibre contents were prepared from silane sized basalt fibres using extrusion, and injection moulding, while composites with 5–10–15 wt% basalt fibre contents were also prepared by using untreated basalt fibres as control. The properties of the injection moulded composites were extensively examined by using quasi-static (tensile, three-point bending) and dynamic mechanical tests (notched and unnotched Charpy impact tests), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), heat deflection temperature (HDT) analysis, dimensional stability test, as well as melt flow index (MFI) analysis and scanning electron microscopic (SEM) observations. It was found that silane treated chopped basalt fibres are much more effective in reinforcing Poly(lactic acid) than natural fibres; although basalt fibres are not biodegradable but they are still considered as natural (can be found in nature in the form of volcanic rocks) and biologically inert. It is demonstrated in this paper that by using basalt fibre reinforcement, a renewable and natural resource based composite can be produced by injection moulding with excellent mechanical properties suitable even for engineering applications. Finally it was shown that by using adequate drying of the materials, composites with higher mechanical properties can be achieved compared to literature data.
A study on free nanohole volumes in particulate epoxy matrix composites as a function of the aluminum particles content is presented. Specifically, the influence of the filler content in the epoxy matrix on the nanohole volume is analyzed in terms of the mechanical and morphological properties of the composites fabricated. Nanoholes data were measured using positron annihilation lifetime spectroscopy recently published by the authors. Applying the Park-Earmme micromechanical model, these data are interpreted in terms of the thermal stresses generated during the curing process applied during fabrication. Some input parameters of the model were experimentally obtained. In order to obtain a satisfactory description of the evolution of the free nanohole volume in the whole range of filler contents, a contribution due to the matrix-particle interphases is taken into account in the micromechanical model. To this aim, specific information on the interphases was obtained using atomic force microscopy (AFM), scanning electron microscopy (SEM), differencital scanning calorimetry (DSC) and a free-constraint analysis of the positron lifetime data.
In this work, all-polypropylene composites (all-PP composites) were manufactured by injection moulding. Prior to injection moulding, pre-impregnated pellets were prepared by a three-step process (filament winding, compression moulding and pelletizing). A highly oriented polypropylene multifilament was used as the reinforcement material, and a random polypropylene copolymer (with ethylene) was used as the matrix material. Plaque specimens were injection moulded from the pellets with either a film gate or a fan gate. The compression moulded sheets and injection moulding plaques were characterised by shrinkage tests, static tensile tests, dynamic mechanical analysis and falling weight impact tests; the fibre distribution and fibre/matrix adhesion were analysed with light microscopy and scanning electron microscopy. The results showed that with increasing fibre content, both the yield stress and the perforation energy significantly increased. Of the two types of gates used, the fan gate caused the mechanical properties of the plaque specimens to become more homogeneous (i.e., the differences in behaviour parallel and perpendicular to the flow direction became negligible).
This work aimed to study the effect of different ultraviolet (UV) weathering conditions (natural and accelerated) on the photodegradation of polyvinyl chloride (PVC) and wood/polyvinyl chloride (WPVC) composites by considering the structural and physical changes of PVC and WPVC samples as well as examining the photodegradation profiles at different depths from the sample surfaces. The photodegradation of PVC and WPVC composites under natural weathering conditions were lower than those under accelerated weathering conditions. The addition of Tinuvin P stabilizer at 2 phr was sufficient to stabilize PVC and WPVC composites, whereas the presence of wood appeared to accelerate the photodegradation of PVC under both natural and accelerated weathering conditions. When considering the photodegradation profiles at different depths of the samples, it was found that the polyene and carbonyl sequences of PVC and WPVC composites were high at the sample surfaces and tended to decrease rapidly with increasing depth from the specimen surface before stabilizing at a depth of 60 μm for PVC and 80 μm for WPVC composites. The differences in specimen depths for the stabilization of polyene and carbonyl sequences in PVC and WPVC samples implied that the presence of wood particles enhanced the absorption of UV radiation by the WPVC composite samples.
Phenylethynyl terminated novel imide compound based on 1,3-bis(3-aminophenoxy)benzene (APB) and phenylethynyl trimellitic anhydride (PETA) were prepared. The curing behavior of phenylethynyl terminated imide compound was investigated by differential scanning calorimetry and Fourier transform infrared spectrometry. The curing reaction of phenylethynylcarbonyl end group completed at 220°C, and proceeded much faster than that of phenylethynyl end group. Glass transition temperature of the thermosetting resin from phenylethynylcarbonyl terminated novel imide compound determined by dynamic mechanical analysis was almost the same as that of o-cresolnovolac type epoxy resin. In addition, the thermosetting resin from phenylethynylcarbonyl terminated novel imide compound exhibited excellent thermal and dimensional stabilities. These excellent properties of these phenylethynyl terminated imide compound might be due to the incorporation of alkene group or aromatic ring substitutes in the backbones, which might enhance the chain interaction (molecular packing) and reduce the molecular chain mobility.
Cyclic butylene terephthalate oligomers (CBT) were reacted in a ring-opening polymerization with three types of isocyanates: a bifunctional aromatic type, a bifunctional aliphatic type and a polymeric aromatic isocyanate. All reactions took place in a batch mixer. The use of 0.5 to 1 wt% isocyanate led to a dramatic increase in elongation at break of polymerized cyclic butylene terephthalate (pCBT), from 8 to above 100%. The stiffness and strength of the modified pCBT, however, were found to slightly decrease. Proton nuclear magnetic resonance (NMR) analysis shows that the formation of thermally stable amide groups is the dominant chain extension reaction mechanism. Gel content measurements suggest a linear structure for samples containing bifunctional isocyanates while pCBT modified with polyfunctional isocyanate exhibited some gel formation at higher isocyanate content. Melting and crystallization temperatures as well as degree of crystallinity were found to decrease with increasing isocyanate content. No phase separation was detected by scanning electron microscopy (SEM) analysis. Moreover, a high degree of polymerization is deduced due to the absence of CBT oligomer crystals.
Hot and cold non-isothermal crystallization of copolymers having glycolide hard segments and glycolide-cotrimethylene carbonate soft segments was investigated by calorimetry, optical microscopy and synchrotron radiation experiments. The effect of composition and microstructural changes on thermal properties and morphology of crystallized samples was analyzed. Significant differences were found between the nucleation density of spherulites developed during cold crystallization. Crystallizations from the melt were characterized by a lamellar insertion mechanism and a broad distribution of crystal layer widths. By contrast, cold crystallized samples gave rise to practically constant long periods and narrower distributions. Soft segments with high glycolide content were more easily incorporated in the crystalline phase by decreasing the hard segment content of the sample. A significant decrease on the melting point was observed as well as a decrease of the amorphous layer thickness and an increase of the crystalline lamellar thickness when the sample was hot and cold crystallized, respectively.
Twenty-one different commercial-grade engineering polymers, including virgin and composite types, were selected for testing, based on mechanical engineering practices. Three groups were formed according to typical applications: 1) Sliding machine element materials; 2) Mechanically load-carrying machine element materials that are often subjected to friction and wear effects; and 3) Additional two amorphous materials used as chemically resistant materials that have rare sliding load properties. The friction running-in state was tested using a dynamic pin-on-plate test rig. During steady-state friction tests, two pv regimes (0.8 and 2 MPa"ms–1) were analysed by a pin-on-disc test system. Based on the measured forces on ground structural steel, surface friction coefficients were calculated and analysed with respect to the mechanical effects of friction. The friction results were evaluated by the measured mechanical properties: yield stress, Shore D hardness, Young’s modulus and elongation at the break. The three material groups exhibited different trends in friction with respect to changing mechanical properties. Linear (with varying positive and negative slopes), logarithmic and exponential relationships were observed, and occasionally there were no effects observed. At steady-state friction, the elongation at the break had less effect on the friction coefficients. The dynamic sliding model, which correlates better to real machine element applications, showed that increasing hardness and yield stress decreases friction. During steady-state friction, an increase in pv regime often changed the sign of the linear relationship between the material property and the friction, which agrees with the frictional theory of polymer/steel sliding pairs.