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Title: The use of sorbitol-initiated polylactic acid as a coupling agent in resorbable phosphate glass fibre reinforced polylactic acid composites
Author: Perera, Madhavie S.
ISNI:       0000 0004 5923 1225
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2015
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Resorbable phosphate glass fibre (PGF) reinforced polymer composites have been investigated for use as fracture fixation plates. While demonstrating impressive initial properties, these composites have shown poor retention of mechanical properties after immersion in a hydrolytic environment. Existing commercially available coupling agents for conventional glass composites have been of limited value and so novel coupling agents have been created specifically for PGF/ Poly (lactide) composites. Previous work on sorbitol-initiated poly (lactide) (S-PLA) oligomers has shown potential both in single fibre and full body composites. This thesis investigates chain length and concentration optimisation of S-PLA based coupling agents on the interfacial properties of PGF reinforced composites, both as manufactured and throughout degradation. S-PLA was synthesised to three different chain lengths: S-PLA_s, S-PLA_m and S-PLA_l where s is short, m – medium and l – long. The oligomers were characterised via NMR, GPC, DSC and FTIR. 40P2O5-24MgO-16CaO-16Na2O-4Fe2O3 (P40) PGF fibres were produced and coated with S-PLA_s, S-PLA_m and S-PLA_l oligomers. It was found that the optimum coating concentration depended on the chain length of the oligomer. Initial tensile strength of the coated fibres increased compared to control though the increase was only significant for S-PLA_s coated fibres. A subsequent degradation study of the fibres in phosphate buffered saline (PBS) at 37 °C for 7 days showed that the tensile strength of the coated fibres decreased significantly compared to that of the control uncoated fibres. S-PLA_l coated fibres had better retention of the tensile strength than the medium and short chain coated fibres. Initial IFSS of embedded S-PLA coated fibres increased significantly compared to that of control but did not differ significantly from each other. A degradation study was conducted for single fibre composites with embedded control and coated fibres immersed in PBS at 37 °C for 7 days. Uncertainty in the true fibre strength during degradation made the IFSS of degraded single fibre composites inconclusive. Full-body composite studies were undertaken to investigate further. Two different methods of application of S-PLA_s on to UD fibre mats were considered: dip coating and spray coating. Composite longitudinal and transverse flexural properties were assessed prior to and after degradation in PBS at 37 °C. The coupling agent improved initial flexural properties and was effective in retaining composite properties for up to 14 days. S-PLA spray coated UD composite samples was more effective in retaining interfacial properties. Water uptake and wet mass change in longitudinal and transverse samples were stable up to 14 days after an initial increase seen at day 1. After day 14 a significant increase in water uptake and wet mass was observed for control composite samples compared to S-PLA coated samples. SEM micrographs and an increase in acidity observed at these time points show advanced fibre dissolution. XRD analysis for composite samples showed a crystallization peak at ~16.5° that did not increase in intensity throughout the degradation period indicating that the crystalline phase did not change during the study. The chain length of S-PLA did not appear to affect the IFSS if the appropriate coating concentration was selected. S-PLA_s was selected due to ease of manufacture however the effect of the other chain lengths on macroscopic composite properties needs to be investigated. The method of coupling agent application onto fibre mats did not appear to make a difference in initial mechanical properties; however the spray coating method shows potential in retarding degradation. This requires further investigation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)