Effect of pre-treatment and heat treatment on tensile and thermal behavior of Parawood strands

This study was carried out to investigate the effect of pre-treatment and heat treatment at varied temperature and timeon tensile and thermal behavior of Parawood strands. A three-way factorial experiment was employed with ten replications.The factors are (1) pre-treatment conditions of three levels (oven-dried strand, EMC strand, boiled strand), (2) temperatureof heat treatment of four levels (170oC, 180oC, 190oC, 200oC) and (3) time of heat treatment of four levels (15 min, 30 min,45 min, 60 min). The specimens prepared from the heat-treated strands were tested in tension parallel to grain and analyzedusing thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Moreover, the specimens were examinedusing scanning electron microscopy (SEM) to reveal its internal structure. The results indicated that the Parawood strands subjected to the pre-treatment by boiling in water (100oC) for 30 minutes and subsequently heat treated in a hot air oven at 190oC for 30 minutes yielded highest tensile strength of 57 MPa and highest toughness of 0.75 MPa. The resulted tensile strength and toughness of boiling pre-treated strands are about 30 and 79 percent higher than those of the oven-dried pre-treated strands, respectively. The specimens subjected to the aforementioned treatment also required highest capacity of endothermic heat of 215 J/g for decomposing its modified crystalline structure. This study suggested that the pre-treatment by boiling in water for 30 minutes, followed by heat treatment at 190oC for 30 minutes, could increase tensile strength and toughness of Parawood strands by increasing its modified crystalline regions (a cellulose crystalline region reinforced by hygrothermally modified lignin and hemicellulose molecules).