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      The Influence of Fibre Processing and Treatments on Hemp Fibre/Epoxy and Hemp Fibre/PLA Composites

      Islam, Mohammad Saiful
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      Islam, M. S. (2008). The Influence of Fibre Processing and Treatments on Hemp Fibre/Epoxy and Hemp Fibre/PLA Composites (Thesis, Doctor of Education (EdD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/2627
      Permanent Research Commons link: https://hdl.handle.net/10289/2627
      Abstract
      In recent years, due to growing environmental awareness, considerable attention has been

      given to the development and production of natural fibre reinforced polymer (both

      thermoset and thermoplastic) composites. The main objective of this study was to

      reinforce epoxy and polylactic acid (PLA) with hemp fibre to produce improved

      composites by optimising the fibre treatment methods, composite processing methods,

      and fibre/matrix interfacial bonding.

      An investigation was conducted to obtain a suitable fibre alkali treatment method to:

      (i) remove non-cellulosic fibre components such as lignin (sensitive to ultra violet

      (UV) radiation) and hemicelluloses (sensitive to moisture) to improve long term

      composites stability

      (ii) roughen fibre surface to obtain mechanical interlocking with matrices

      (iii)expose cellulose hydroxyl groups to obtain hydrogen and covalent bonding with

      matrices

      (iv) separate the fibres from their fibre bundles to make the fibre surface available for

      bonding with matrices

      (v) retain tensile strength by keeping fibre damage to a minimum level and

      (vi) increase crystalline cellulose by better packing of cellulose chains to enhance the

      thermal stability of the fibres.

      An empirical model was developed for fibre tensile strength (TS) obtained with different

      treatment conditions (different sodium hydroxide (NaOH) and sodium sulphite (Na2SO3)

      concentrations, treatment temperatures, and digestion times) by a partial factorial design.

      Upon analysis of the alkali fibre treatments by single fibre tensile testing (SFTT),

      scanning electron microscopy (SEM), zeta potential measurements, differential thermal

      analysis/thermogravimetric analysis (DTA/TGA), wide angle X-ray diffraction

      (WAXRD), lignin analysis and Fourier transform infrared (FTIR) spectroscopy, a

      treatment consisting of 5 wt% NaOH and 2 wt% Na2SO3 concentrations, with a treatment temperature of 120oC and a digestion time of 60 minutes, was found to give the best

      combination of the required properties. This alkali treatment produced fibres with an

      average TS and Young's modulus (YM) of 463 MPa and 33 GPa respectively. The fibres

      obtained with the optimised alkali treatment were further treated with acetic anhydride

      and phenyltrimethoxy silane. However, acetylated and silane treated fibres were not

      found to give overall performance improvement.

      Cure kinetics of the neat epoxy (NE) and 40 wt% untreated fibre/epoxy (UTFE)

      composites were studied and it was found that the addition of fibres into epoxy resin

      increased the reaction rate and decreased the curing time. An increase in the nucleophilic

      activity of the amine groups in the presence of fibres is believed to have increased the

      reaction rate of the fibre/epoxy resin system and hence reduced the activation energies

      compared to NE.

      The highest interfacial shear strength (IFSS) value for alkali treated fibre/epoxy (ATFE)

      samples was 5.2 MPa which was larger than the highest value of 2.7 MPa for UTFE

      samples supporting that there was a stronger interface between alkali treated fibre and

      epoxy resin. The best fibre/epoxy bonding was found for an epoxy to curing agent ratio of

      1:1 (E1C1) followed by epoxy to curing agent ratios of 1:1.2 (E1C1.2), 1: 0.8 (E1C0.8), and

      finally for 1:0.6 (E1C0.6).

      Long and short fibre reinforced epoxy composites were produced with various processing

      conditions using vacuum bag and compression moulding. A 65 wt% untreated long

      fibre/epoxy (UTLFE) composite produced by compression moulding at 70oC with a TS of

      165 MPa, YM of 17 GPa, flexural strength of 180 MPa, flexural modulus of 10.1 GPa,

      impact energy (IE) of 14.5 kJ/m2, and fracture toughness (KIc) of 5 MPa.m1/2 was found to

      be the best in contrast to the trend of increased IFSS for ATFE samples. This is

      considered to be due to stress concentration as a result of increased fibre/fibre contact

      with the increased fibre content in the ATFE composites compared to the UTFE

      composites.

      Hygrothermal ageing of 65 wt% untreated and alkali treated long and short fibre/epoxy

      composites (produced by curing at 70oC) showed that long fibre/epoxy composites were

      more resistant than short fibre/epoxy composites and ATFE composites were more

      resistant than UTFE composites towards hygrothermal ageing environments as revealed from diffusion coefficients and tensile, flexural, impact, fracture toughness, SEM, TGA,

      and WAXRD test results. Accelerated ageing of 65 wt% UTLFE and alkali treated long

      fibre/epoxy (ATLFE) composites (produced by curing at 70oC) showed that ATLFE

      composites were more resistant than UTLFE composites towards hygrothermal ageing

      environments as revealed from tensile, flexural, impact, KIc, SEM, TGA, WAXRD, FTIR

      test results.

      IFSS obtained with untreated fibre/PLA (UFPLA) and alkali treated fibre/PLA (ATPLA)

      samples showed that ATPLA samples had greater IFSS than that of UFPLA samples. The

      increase in the formation of hydrogen bonding and mechanical interlocking of the alkali

      treated fibres with PLA could be responsible for the increased IFSS for ATPLA system

      compared to UFPLA system.

      Long and short fibre reinforced PLA composites were also produced with various

      processing conditions using compression moulding. A 32 wt% alkali treated long fibre

      PLA composite produced by film stacking with a TS of 83 MPa, YM of 11 GPa, flexural

      strength of 143 MPa, flexural modulus of 6.5 GPa, IE of 9 kJ/m2, and KIc of 3 MPa.m1/2

      was found to be the best. This could be due to the better bonding of the alkali treated

      fibres with PLA. The mechanical properties of this composite have been found to be the

      best compared to the available literature.

      Hygrothermal and accelerated ageing of 32 wt% untreated and alkali treated long

      fibre/PLA composites ATPLA composites were more resistant than UFPLA composites

      towards hygrothermal and accelerated ageing environments as revealed from diffusion

      coefficients and tensile, flexural, impact, KIc, SEM, differential scanning calorimetry

      (DSC), WAXRD, and FTIR results. Increased potential hydrogen bond formation and

      mechanical interlocking of the alkali treated fibres with PLA could be responsible for the

      increased resistance of the ATPLA composites.

      Based on the present study, it can be said that the performance of natural fibre composites

      largely depend on fibre properties (e.g. length and orientation), matrix properties (e.g.

      cure kinetics and crystallinity), fibre treatment and processing methods, and composite

      processing methods.
      Date
      2008
      Type
      Thesis
      Degree Name
      Doctor of Education (EdD)
      Publisher
      The University of Waikato
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