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与机械压缩作用使样品致密化；通过调整时间、温度与压力的不同组合，可提升木材密度并改善其部分性能。本研究旨在对帕里卡胶合板进行热机械处理，并观察其对材料物理与力学性能的影响。试验试样分为两组，分别在120℃与150℃下进行处理，保压7分钟，随后卸压并维持15分钟。试验结果显示，试样比质量（specific mass）从0.48 g·cm⁻³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：处理后的试样吸水膨胀程度与吸水率均高于未处理试样，且厚度不可逆膨胀率更高。这表明本次热机械处理未释放板材压制过程中产生的内部压应力，因此未能改善材料的尺寸稳定性。另一方面，力学性能得到正向提升：经120℃与150℃处理的试样，其静曲模量（modulus of rupture, MOR）分别提升27.5%与51.8%；弹性模量（modulus of elasticity, MOE）与胶层剪切强度无统计学显著性差异，而经150℃处理后的詹卡硬度（Janka hardness）提升29.7%。