Manufacturing of wheat straw particleboards based on the mixture of MF and UF resins

In order to manufacture wheat straw particleboards, different mixtures of UF and MF resins were applied. The ratio of UF: MF was 0:100,75:25,50:50,25:75 and 100:0 based on resin weight. Boards densities were set as 0.7gr/cm3.Physical and mechanical properties such as thickness swelling(TS) after 2 and 24 hours, internal bonding(IB), modulus of elasticity(MOE), modulus of rupture(MOR) were measured and compared to EN 312-4 standard. The highest amounts of IB, MOR and MOE were from the boards made of 50:50 (UF:MF). All of the boards MOE and MOR amounts of the treatments except for the treatment 100:0 (UF:MF) were in the range of EN 312-4 standard but the IB amounts did not comply. The TS amount was improved in the boards with more MF content but it was not in EN 312-4 range. Due to the thin waxy layer covers the outer most layer of wheat straw surface, the non polar structure of this layer brings low-compatibility between polar resins and wheat straw particles which will result in poor physical and mechanical properties for wheat straw particleboards. Also due to the low porosity of waxy layer, the penetration of polar formaldehyde resins into straw particles surface, not well occur and this is itself an important factor in low physical and mechanical resistance in wheat straw particleboards that in the case of wood.