Sheet-molded polyolefin natural fiber composites for automotive applications

The use if natural fibers as reinforcing filler in thermoplastics is a relatively new application and has great potential in replacing glass fiber products in automotive industry. However, most of the research in this area has been focused primarily on flax fiber. In the first part of the work presented here, hemp fiber non-woven mats are used exclusively in combination with a poly(propylene) matrix to study the mechanical properties of natural fiber mat thermoplastics (NMT) in the absence of binder. Film stacking was used as the method of preparation. The results show that hemp-based NMT have comparable or even higher strength properties as compared with conventional flax-based thermoplastics. A value of 63 MPa for the flexual strength is achieved at a fiber content of 64 wt. %. The influence of the compression ratio on the mechanical properties and density of NMT also reported. A definite increase in strength is observed with increasing compression together with a much more uniform density profile. In the second part of this study, a unique combination of random hemp fibers, non-woven mats and poly(propylene) films was employed in film stacking to evaluate strength properties and economic implications. The same fiber content (64 wt.-%) was maintained in the final NMT by replacing 78 wt.-% of the mats by random fibers. Preliminary tests reveal better mechanical properties especially in terms of impact energy, which is 50 to 100% higher, as compared with different mats-only/poly(propylene) combinations. Further, a net saving of 40% in fiber cost is anticipated by replacing 78% non-woven mats with an equivalent amount of random fibers. Overall results of this study indicate that hemp-based NMT are promising candidates in automotive applications where high specific stiffness is required.