EFFECT OF THERMO-MECHANICAL TREATMENT ON PROPERTIES OF PARICA PLYWOODS (Schizolobium amazonicum Huber ex Ducke)

ABSTRACT Thermo-mechanical treatment is a technique for wood modification in which samples are densified by means of heat and mechanical compression, applied perpendicularly to fibers, which under different combinations of time, temperature, and pressure increases wood density and thus improve some of its properties. This study aimed to treat thermo-mechanically parica plywood and observe the effects on its physical and mechanical properties. Specimens were submitted to two treatments, 120 and 150 ºC, remaining under pressure for seven minutes and, subsequently, under zero pressure for 15 minutes. Results showed a significant increase in specific mass from 0.48 g cm-3 to an average of 0.56 g cm-3, and a compression ratio of about 31.7% on average. Physical properties also varied significantly and results showed that treated samples swelled and absorbed more water than those untreated, leading to a greater thickness non-return rate. This indicates the proposed thermal treatments did not release the internal compressive stress generated during panel pressing, not improving its dimensional stability as a result. On the other hand, mechanical properties were positively affected, leading to an increase of 27.5% and 51.8% in modulus of rupture after treatments at 120 and 150 ºC, respectively. Modulus of elasticity and glue-line shear strength did not vary statistically and Janka hardness was 29.7% higher after treatment at 150 ºC.

摘要：热机械处理（Thermo-mechanical treatment）是一种木材改性技术，通过垂直于纤维方向施加热作用与机械压缩使试样致密化。在时间、温度与压力的不同组合条件下，该工艺可提升木材密度，进而改善其部分性能。本研究旨在对帕里卡胶合板进行热机械处理，并观察其对板材物理与力学性能的影响。试验试样接受两种处理工艺，分别为120℃与150℃，处理过程中先保压7分钟，随后卸压保持15分钟。
结果显示，试样的体积密度从0.48 g·cm⁻³显著提升至平均0.56 g·cm⁻³，平均压缩率约为31.7%。物理性能同样出现显著变化：经处理的试样相较于未处理试样，吸水膨胀程度与吸水量更高，进而导致更高的厚度不可逆回复率。这表明本次采用的热处理工艺未能释放板材压制过程中产生的内部压应力，因此未能改善板材的尺寸稳定性。
另一方面，力学性能得到了积极改善：经120℃与150℃处理后的试样，其抗弯强度分别提升27.5%与51.8%。抗弯弹性模量与胶合层剪切强度未出现统计学意义上的显著变化，而经150℃处理后的试样扬卡硬度（Janka hardness）提升了29.7%。