Hemp fibre as alternative to glass fibre in sheet moulding compound. Part 2—impact properties

Abstract

This paper describes the results of falling weight impact tests on natural fibre reinforced polyester composites fabricated using a conventional sheet moulding compound (SMC) process. The influence of hemp fibre and CaCO 3 filler content on the penetration energy of hemp fibre reinforced sheet moulding compound (H-SMC) is reported and compared with glass fibre reinforced sheet moulding compound (G-SMC). To evaluate the influence of fibre/matrix interfacial adhesion on the impact behaviour of these H-SMCs, the hemp fibres were treated with alkaline and silane treatments, as well as a combination of these treatments. A simple mechanistic model is proposed for these natural fibre composites and is used to obtain more insight into the impact behaviour of the composites as well as to provide guidelines to compare the experimental data with theory.

Investigating the impact behaviour of short hemp fibres reinforced polypropylene biocomposites through high speed imaging and finite element modelling

“…For these authors, cohesive interfaces obtained by fibre treatments such as organosilanes only promoted increases in tensile stiffness and strength to the detriment of impact properties. In contrast, Patel et al [5] found that fibre surface treatments (silane and alkaline) promoting interfacial cohesion led to higher absorbed energy upon impact for hemp fibre reinforced polyester composites.…”

“…Santulli et al [7][8][9] compared the impact behaviour of a flax / epoxy composite to a glass / epoxy composite with similar weight ratio reinforcement on a drop-weight impact test, and found a better impact resistance for the glass reinforced ones. Patel et al [5] and Scarponi et al [6] also showed that glass fibres reinforced polyester and epoxy composites have a slightly higher energy absorbed at breakage than hemp reinforced biocomposites. However at low fibre volume fraction (< 20 vol%), the difference was much smaller.…”

“…Biocomposites could thus exhibit a good penetration resistance even after damage initiation. Besides, Patel et al [5] also found that for low fibre volume fraction (< 20 vol%), the differences in absorbed energy between glass and natural fibres composites were not significant. Caprino et al [10][11][12] pointed out that epoxy-hemp biocomposites needed higher impact energy to initiate damage when compared to epoxy-glass composites.…”

“…Several authors compared the impact behaviour of natural fibre reinforced composites to traditional glass fibre ones [5][6][7][8][9][10][11][12]. Among them, Patel et al [5], Scarponi et al [6], and Santulli et al [7][8][9] showed that for glass fibre reinforced epoxy and polyester resins, peak loads and absorbed energies at breakage were higher than those of hemp fibre reinforced composites, but the latter exhibited a higher strain at break. Santulli et al [7][8][9] postulated that the difference in absorbed energy between natural fibres (jute, flax and hemp) and glass reinforced epoxy composites was due to a shorter elastic phase upon impact loading in the case of biocomposites leading to lower peak loads as compared to glass fibre reinforced composites.…”

“…This result suggests that natural fibre composites can have comparable impact damage tolerance as glass fibre composites. Moreover, an interface treatment such as alkaline, silane or a combination of both could even increase the energy absorbed by the biocomposites upon impact [5]. Most of the studies dealing with impact behaviour of natural fibres reinforced composites were mainly based on uniaxial impact tests such as Izod or Charpy tests [13,14].…”