Dissertation in Forest industrial production systems, Nicolas Neitzel

Abstract

The intensified demand for renewable materials, rising wood prices and increasing protection zones of forest areas make the wood panel industry consider alternative raw materials. The agricultural sector provides, at the same time, large amounts of lignocellulosic materials.

This thesis explored the potential of agro-industry feedstocks and side streams as raw materials for wood panel manufacturing based on a literature review and experimental tests. The material characteristics of barley husk (BH), oat husk (OH) and wheat bran (WB) were analysed in detail. It was found that BH and OH have at 70% and 66% a slightly lower holocellulose content than wooden materials (poplar, spruce), while their hemicellulose content exceeds that of cellulose. Micromechanical tests showed that OH could resist a higher ultimate stress load than BH and WB, but the modulus of elasticity, affected by the microfibril angle, was lower. OH was suggested as promising raw material and evaluated for particleboard manufacturing. In an experimental investigation, OH was explored as raw material in a special particleboard type, i.e., tubular particleboards. Although the boards showed higher insulation properties than wood particle-based ones, the mechanical properties were considerably affected by the reduced wettability, and the manufacturing method led to poor density distribution.

In addition, the agricultural feedstock wheat starch, in combination with microfibrillated cellulose (MFC) and emulsifiable diphenylmethane diisocyanate (eMDI), was investigated as an adhesive system for fibreboard production. Wheat starch was modified to dialdehyde starch (DAS) and served as the backbone in an adhesive formulation of 99.5% bio-based content using 1% MFC and 4% eMDI based on DAS, which showed excellent mechanical and water resistance performance in fibreboards. The DAS-based adhesive was used to bond OH in particleboards, whereas challenges in practical implementation were encountered. The severely shortened starch molecule reacted with the proteins of the OH, and from temperatures of 160°C, it led to accelerating degradation and reduced bonding capacity of the adhesive.

Finally, this thesis provided a deeper knowledge of husked-based raw materials' properties in the context of panel manufacturing and showed that they are a possible but challenging alternative to wood. The investigation of a DAS-based adhesive opened a promising path for bio-based adhesives and the independence of formaldehyde systems.