JEC COMPOSITES MAGAZINE - Issue #71 - March 2012 - 112

automotive

cellulose and wheat straw have been investigated in injection moulding grade materials, primarily in polyolefin resins. The following is a case study for wheat straw-reinforced polypropylene (WSPP). Wheat straw fibre, a co-product of the wheat harvest, is a bast fibre that can be grown in many parts of the globe Fig. 4: Timeline for the development of wheat straw-reinforced composite. Project initiation to vehicle implementation was and has very little approximately 20 months use outside of animal bedding. The objective development of WSPP from concepprocessability, and inhibit oxidation in the development of this technology tion to commercialization. The timeline and degradation. The initial target was was to replace glass fibre or mineral for this case study comprised only 20 to match the mechanical performance reinforcements in injection moulding months, which is highly compressed of talc-reinforced polypropylene grade compounds to achieve the same versus the typical case for the autohomopolymer. Table 1 shows physical performance and durability while redumotive industry. This was due to the properties of 20% and 40% loadings cing CO2 emissions and density. inclusion of all key stakeholders from of wheat straw-reinforced PP compaThe development team included parthe project start. red to talc-reinforced PP at the same tners and stakeholders from throughout Wheat straw fibre was cleaned and weight percentage loadings. Due to the the supply chain to the end user. These milled to a uniform length and aspect decreased density of wheat straw versus included: research institution, raw ratio prior to melt compounding with talc, a significant decrease in composite material supplier (farm), natural fibre polypropylene (PP). Although the fibre density was achieved. Although a slight processor, compounder/Tier 3 material itself was not treated, compatibilizers decrease in tensile strength and flexural supplier, moulder/Tier 1 supplier and and other additives were used in the modulus was observed, notched Izod end user/automotive OEM. composite formulation to enhance the impact and heat distortion tempeFigure 4 shows the timeline for the fibre-matrix interface, improve flow and rature (HDT) were improved. This initial screening of properties allowed Tab. 1: Physical property comparison of wheat straw reinforcement versus talc reinforcement in polyprofor an assessment of feasibility and pylene the selection of automotive material 20% 20% 40% 40% specification. Physical talc wheat straw talc wheat straw Figures 5 and 6 show radar plots of property WSPP formulations compared to 3 existing Ford material specifications. 1.01 0.96 1.16 1.030 Desnity (g/cm ) In Figure 5, a 20% WSPP formulation is compared with a heat-stabilized, Tensile Str 25.5 23.2 26.4 25.7 20% mineral-reinforced PP homo@ yield (MPa) polymer with 25% recycled content. Flexural modulus The plots are normalized to show the 2107 1962 3265 2979 (MPa) specification requirement at 100%. The figure shows that a direct replaceNotched Izod 4.2 4.6 2.7 3.8 ment of mineral with WS yields similar @ 23°C (kJ/m2) properties, only falling short for tensile strength. Note that the differences in HDT @ 0.45 MPa 100.6 114 115.7 138.1 melt flow rate and shrink rate can be (°C) taken into account during processing Mold shrink, and tool making. Small optimizations 0.94 0.75 0.76 0.52 48 hrs @ 23°C(%) were made to increase the tensile

112 jec composites magazine / No71 March 2012

JEC COMPOSITES MAGAZINE - Issue #71 - March 2012

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