The effect of different fibre volume fractions of hemp and nanoclay reinforcement on the mechanical, thermal and environmental properties of unsaturated polyester composites has been investigated experimentally. Due to the incorporation of different fibre volume fractions of hemp into polyester resin an improvement in tensile strength and tangent modulus was realised. Likewise, the flexural strength and modulus of unsaturated polyester (UPE) matrix increased with the introduction of hemp fibre. The mechanical tests results suggest that the tensile and flexural properties of composites are related to the fibre volume fractions and interfacial bond strengths between the fibre and matrix. Flexural properties of the composites were found to be comparable to those of chopped strand mat (CSM) glass fibre reinforced UPE composites. Low velocity instrumented falling weight impact tests were conducted to evaluate impact and damage characteristics of hemp and nanoclay reinforced composites. A significant improvement in load bearing capability and impact energy absorption was found by introducing hemp fibre and nanoclay as reinforcement. The impact test results in this study show that the total energy absorbed by the 0.21 fibre volume fraction of hemp reinforced specimen is comparable to the energy absorbed by the composites specimen equivalent in fibre weight percentage of CSM E-glass fibre. All nanoclay reinforced nanocomposite specimens have shown a significant improvement in their impact strength and energy absorption properties compared to unreinforced UPE matrix. The effects of various loading levels of nanoclay reinforcement on the nanomechanical properties of UPE/layered silicate nanocomposites were investigated by a nanoindentation test method. It has shown that the nanoindentation behaviour is strongly influenced by nanoclay reinforcement and the extent of clay dispersion in the polymer matrix. The creep behaviour of hemp fibre reinforced unsaturated polyester (LIFRUPE) composites was investigated using a three-point bending clamp system. Creep strain decreased as the hemp fibre reinforcement increased. The creep deflection value was significantly higher for unreinforced samples compared to hemp fibre reinforced samples. Thermal properties were evaluated using Thermogravimetric Analysis (TGA), Thermo Mechanical Analyser (TMA), Differential Scanning Calorimetry (DSC) and thermal conductivity analysis. TGA results suggest that various concentrations of nanoclay and hemp reinforcement increases the thermal stability of UPE/layered silicate nanocomposites and IIFRUPE composites. Glass transition temperatures (Tg) were also increased with the introduction of clay and hemp fibre reinforcement. Hemp reinforced specimens also showed increased thermal stability indicated by an increased Tg value and decreased decomposition rate. Thermal conductivity values were found to be higher for both clay and hemp reinforced specimens compared to unreinforced polyester. Different fibre volume fraction of HFRUPE composites were subjected to water immersion tests in order to study the effects of water absorption on a range of properties. Water absorption tests were conducted by immersing specimens in a de-ionised water bath at room temperature and 100 °C for different time durations. The tensile, flexural and nanohardness properties of water immersed specimens subjected to both aging conditions were evaluated and compared alongside dry composite specimens. The percentage of moisture uptake increased as the fibre volume fraction increased. The tensile, flexural and nanohardness properties of HFRUPE specimens were found to decrease with increase in percentage moisture uptake. However, the impact properties of HFRUPE composites were found increased after water immersion. Moisture induced degradation of composite samples was significant at elevated temperature. The water absorption pattern of these composites at room temperature was found to follow Fickian behaviour, whereas at elevated temperatures it exhibited non- Fickian. Keywords: Polymer matrix composites (PMCs); Layered silicate nanocomposites; Natural fibre reinforced composites (NFRC); Mechanical properties; Mechanical testing; Moisture absorption; Thermal stability
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:503594 |
| Date | January 2006 |
| Creators | Dhakal, Hom Nath |
| Publisher | University of Portsmouth |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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