Air-laid and foam-laid nonwoven composites: The effect of carrier medium on mechanical properties

Thermoplastic nonwoven composites were produced with the air-laying and foam-forming processes from cellulosic and plastic fibers. The two raw material combinations were (1) PP/PE (fiber length 3 mm), PP/PE (12 mm), fluff pulp fibers (2 mm) and (2) PP/PE (3 mm), fluff pulp fibers, viscose (10 mm). After forming, the fibrous sheets (400 gsm) were bonded with heat pressing (145°C). The effect of the carrier medium, air or aqueous foam, on the tensile and impact properties and sheet structure was explored. The air-laids differed from the foam-laids by sheet anisotropy, density, and the lack of an additional bonding regime between wood fibers due to the dry forming process. The PP/PE bonding fibers gave the air-laids a good capacity to elongate compared to the foam-laids. The advantage was lost when nonbonding viscose was added. The impact strength was dependent on the PP/PE dosage and the sheet density, rather than the moisture-induced bonding between wood fibers. The changing long/short fiber ratios caused gradual shifts in sheet properties, usually a reduction in a mechanical property as the share of short fiber increased in the mix. Economic analysis revealed that increasing fluff content can reduce raw material costs, providing a possibility for cost optimization in total production costs.