Temperature dependence of the interfacial shear strength in glass reinforced polypropylene and epoxy composites

We have recently reported the development of a method which allows the measurement of IFSS over a wide temperature range [6,7]. In this paper we present data obtained using the microbond test in the temperature controlled environment of a thermo-mechanical analyser (TMA). IFSS in glass fibre–polypropylene and glass fibre-epoxy systems in the temperature range -40°C to 150°C are presented and discussed

The role of residual thermal stress in interfacial strength of polymer composites by a novel single fibre technique

The temperature dependence of the interfacial properties of glass fibre reinforced polypropylene and epoxy composites was investigated using a novel microbond test in the temperature controlled environment of a thermo-mechanical analyser. Highly significant inverse dependence of IFSS on testing temperature was observed in both systems. The temperature dependence of the GF-PP IFSS was accounted for by the variation of residual radial compressive stresses at the interface with the test temperature. On the other hand, it was found that the residual thermal stress did not seem to fully account for the temperature dependence of IFSS in GF-Epoxy. Nevertheless, the results clearly showed that GF-Epoxy IFSS had a strong correlation with the modulus of the epoxy matrix

Development and application of micromechanical techniques for characterising interfacial shear strength in fibre-thermoplastic composites

The development of single fibre pull-out and microbond tests for characterising interfacial strength in thermoplastic composites is reviewed in detail. Manufacture of an experimental jig and sample preparation regimes for both tests are described. The challenges addressed in the sample preparation include the measurement of embedded fibre length for pull-out samples and the low yield rate of axisymmetric resin droplets obtained during sample preparation under nitrogen. The applications of these laboratory developed techniques are demonstrated by characterisation of the interfacial shear strength (IFSS) of glass fibre-polypropylene (GF-PP) and natural fibre-polylactic acid (NF-PLA). The comparison of the IFSS between neat and modified GF-PP showed that both methods were sensitive to the interfacial performance change despite the poor agreement between them for the absolute IFSS values from the same composite. The effect of the material modification was also reflected in load-displacement curves with different behaviour of the frictional motion after complete debonding. When a high level of fibre-matrix adhesion was realised in the composites with weak fibres, the microbond test showed higher feasibility for characterising the IFSS. This was clearly shown in its application to NF-PLA

Effect of Silane coupling agent on mechanical performance of glass fibre

Mechanical performance of commercially manufactured unsized and γ-APS sized boron-free E-glass fibres has been characterised using single fibre tensile test. Both apparent fibre modulus and fibre strength were found to strongly depend on fibre gauge length. The average strength of sized fibres was found 40%-80% higher than unsized fibres at different gauge lengths. Weibull analysis suggested that the failure mode of unsized fibres could be described by unimodal Weibull distribution, whereas the strength distribution of sized fibres appeared to be controlled by two exclusive types of flaw population, type A and B. Comparison of the Weibull plots between unsized and sized fibres revealed that the strength of unsized fibres was likely to be dominated by type A flaws existing on the bare glass surface and type B flaws may be related to the defects on the glass surface coated with silane. This was partially supported by the observation of fractured cross-sectional area using SEM. It was, therefore, proposed that the strength difference between unsized and sized glass fibres may be more reasonably interpreted from the surface protection standpoint as opposed to the flaw healing effect. The results obtained from this work showed that silane coupling agent plays a critical role in the strength retention of commercially manufactured E-glass fibres and the silane effect on the fibre strength is also affected by the change in gauge length of the sample

An efficient one-step site-directed deletion, insertion, single and multiple-site plasmid mutagenesis protocol

Background: Mutagenesis plays an essential role in molecular biology and biochemistry. It has also been used in enzymology and protein science to generate proteins which are more tractable for biophysical techniques. The ability to quickly and specifically mutate a residue(s) in protein is important for mechanistic and functional studies. Although many site-directed mutagenesis methods have been developed, a simple, quick and multi-applicable method is still desirable. Results: We have developed a site-directed plasmid mutagenesis protocol that preserved the simple one step procedure of the QuikChange (TM) site-directed mutagenesis but enhanced its efficiency and extended its capability for multi-site mutagenesis. This modified protocol used a new primer design that promoted primer-template annealing by eliminating primer dimerization and also permitted the newly synthesized DNA to be used as the template in subsequent amplification cycles. These two factors we believe are the main reasons for the enhanced amplification efficiency and for its applications in multi-site mutagenesis. Conclusion: Our modified protocol significantly increased the efficiency of single mutation and also allowed facile large single insertions, deletions/truncations and multiple mutations in a single experiment, an option incompatible with the standard QuikChange (TM). Furthermore the new protocol required significantly less parental DNA which facilitated the DpnI digestion after the PCR amplification and enhanced the overall efficiency and reliability. Using our protocol, we generated single site, multiple single-site mutations and a combined insertion/deletion mutations. The results demonstrated that this new protocol imposed no additional reagent costs (beyond basic QuikChange T) but increased the overall success rates.Publisher PDFPeer reviewe