Extrusion fractionation of wheat straw for biocomposites utilising the entire straw constituents

Biocomposite boards from wheat straw without addition of bonding agent

“…The NaOH treatment (comparing boards from the medium straw: MB2 and TMB2) has resulted in a significant increase in density (13?6%) showing that it is able to soften the lignin-hemicellulose bonding between straw fibres and given rise to higher compressibility. 7 Density reflects the initial packing efficiency and compressibility of straw under the combined temperature and pressure. Packing efficiency is influenced by geometric aspects of particulate materials such as particle shape, size distribution, surface roughness and 19 For instance, higher aspect ratio (length/diameter for fibrous particulates) normally leads to initial poor packing before compression and stronger mechanical interlocking between straws under compression, restricting mobility and giving rise to lower density.…”

“…The NaOH treatment (comparing boards from the medium straw: MB2 and TMB2) has resulted in a significant increase in density (13·6) showing that it is able to soften the lignin–hemicellulose bonding between straw fibres and given rise to higher compressibility. 7…”

“…Adhesive bonding provided by the natural resin liberated from the native straw and mobilised to the interface. It may be facilitated chemically by the alkali treatment as demonstrated in the TMB2 boards and, to 7 Comparison of flexural modulus before and after 'stress plateau' (nominal and secondary modulus) 8 Flexural stress-strain curves of straw boards compression moulded from untreated straws showing effect of NaOH pretreatment on wheat straw a delamination of boards (MB2) from non-NaOH pretreated straw; b NaOH pretreated boards (TMB2) showing absence of delamination 9 Fracture at different stages of flexural test of straw boards showing effect NaOH pretreatment some extent, physically by applying heat and pressure for the non-alkali treated boards. Within the variation of straw preparation and compression conditions studied, the density ranges between 1100 and 1350 kg m 23 , and maximum flexural modulus and strength are 2?4 GPa (TMB2) and 16 MPa (MC3) respectively.…”

“…This involves high energy consumption during the processes and resulted in large quantities of complex effluent or black liquor, which can be costly to treat. Kang et al 7 reported that wheat straw feedstock from alkaline pretreatment followed by extrusion fractionation could be compression moulded without the addition of any resin in a simple board production process that combines heating and compression. The non-cellulose constitute (lignin and hemicellulose) leached out from the native straw structure acts as a binder in the composites to achieve a good combination of mechanical properties.…”

“…8,9 The extrusion fractionation process, however, incurs additional cost and has been shown to contribute to fibre damage. 7 It is highly desirable therefore to develop a cost effective process for manufacturing straw boards featured by: (i) minimum straw preparation, e.g. using straws in chopped form (ii) simple boards processing, e.g.…”