Properties of Gypsum Boards Made of Mixtures of Wood and Rice Straw

Aims: It was investigated to produce gypsum-based experimental composite panels with red pine wood/rice straw particles in the mixture up to 60:40 (ratio) (w/w) in gypsum-water mixture. In this case, the additives could be observed more closely.

Methodology: The red pine wood chips and the rice straw (stalks) have been turned into suitable particle dimensions. The experimental boards were cut to determine the IB (Internal bond), MOE–MOR (Modulus of Elasticity and Rupture), and TS (thickness swelling after 24 hours immersion in water). A standard flame combustion test system was conducted according to TS EN-ISO 11925-2. For surface chemical analyses, FTIR was used to evaluate the chemical groups present in the board surface. The thermogravimetric analysis (TGA) was conducted for measuring changes in boards as a function of increasing temperature. The natural weathering tests were conducted that were exposed to outdoor for two months then color and surface hardness measurements conducted for determining property changes.

Results: The rice straw had negative impact on thickness swelling (TS) properties of boards in water. The highest TS value of 47.66% was observed in the board that produced from 60:40 (ratio) (w/w) wood/rice straw mixture (DE4). However, the addition of rice straw to the wood/gypsum mixture has a lowering effect on the internal bond (IB) and bending strength (MOR) properties of experimental boards some level. The maximum IB strength of 0.06 N/mm2 and MOR of 2.77 N/mm2 found control sample (DE0). However, the highest MOE value of 553 N/mm2 was calculated on the DE4 board, which was produced by adding 40% rice straw to the wood/gypsum mixture. The addition of rice straw and wood particles to the gypsum structure has a positive effect on the heat transfer properties.

Conclusion: It is clear that the addition of rice straw to the wood/gypsum mixture adversely affected the strength properties negatively. However, rice straw in wood chip/gypsum mixture helps to improve heat resistance (insulation) properties of panels at some level. Moreover, the addition of rice straw to wood/gypsum mixture effects on extending hardening time.