Hemicelluloses extraction and nanocellulose addition as a partial replacement for non-renewable adhesives in oriented strand board.

Abstract

Oriented strand board (OSB) is an engineered wood product used for building wood-based structures (e.g., walls, floors, ceilings, furniture). This composite is manufactured with small pieces of wood (strands) linked together with adhesives and wax, which is added to reduce water absorption. Wood composites are an alternative for satisfying the increased demand for building products and there are several advantages over solid wood. Similarly, to other wood composites, one of the main disadvantages of OSB is the absorption of environmental moisture. Therefore, the applications of wood-composite material are mainly limited by their irreversible thickness swelling. In order to make wood-based panels usable for exterior applications, it is necessary to improve their dimensional stability in high relative humidity conditions. Thus, the first investigation in this work was the pre-treatment of wood strands to increase the hydrophobic performance in final wood-based panels. The hypothesis was that the reduction of hydroxyl groups in wood strands would increase the dimensional stability of OSB. The literature suggests different pre-treatment to reduce hydroxyl groups in wood material. In the present work, pressurized hot water extraction was used, and three different conditions were tested (120, 140 and 160 ºC at 45 min). After wood strand pre-treatment, OSB samples were manufactured and static bending, internal bond, thickness swelling, and water absorption properties were tested using the ASTM D1037 procedures. As a benefit to OSB manufacturers, project results have shown that removal of hemicelluloses with pressurized hot water increases the dimensional stability of the final wood composite. This is attributed to less available hydroxyl groups associated to the presence of hemicelluloses. The pre-treatment at 160 °C resulted in the maximum amount of hemicelluloses extraction and OSB produced with this pre-treated material had the best dimensional stability. The percentage of extracted material increased as reaction temperature increased in the range of temperatures studied. At 120 °C, the percentage of hemicelluloses extracted was reduced but its impact on final OSB mechanical and physical properties was insignificant. The second investigation in this work was the partial replacement of non-renewable polymeric methylene diphenyl diisocyanate (pMDI) adhesive by cellulose nanofibrils (CNF) in OSB. The demand for wood composites has been increasing and consequently so has the demand for pMDI. This has led to several efforts towards replacing non-renewable adhesives with renewable biomaterials. CNF has a high modulus of elasticity; therefore, it could be an opportunity to reinforce and partially replace the pMDI adhesive in OSB. In this work, two experimental designs at different density were conducted, each one with two factors (adhesive and CNF), and three levels (2.7, 4.4, and 6.2 % for adhesive and 0, 3, and 6 % for CNF). Static bending, internal bond, thickness swelling, and water absorption properties were tested on OSB samples using the ASTM D1037 procedures. The result showed that for most of the properties, the CNF did not have a statistically significant effect at the 95.0 % confidence level, for some properties, the effect was positive and for the internal bonding, the effect was negative. For the adhesive, results showed that for most of the properties, it had a statistically significant positive effect at the 95.0 % confidence level. The more adhesive that was added the better the properties were observed.