Mechanical behaviour of acetylated rubber wood subjected to artificial weathering

Abstract

Rubber wood utilization in Nigeria has become a viable alternative because of over-exploitation of more durable species. The use of rubber wood in its native form has some disadvantages including dimensional instability, low durability and susceptibility to weathering in outdoor uses. However, it may be improved through chemical modification such as acetylation. In this study, we revealed the effectiveness of acetylation on the protection of rubber wood against weathering in terms of weight loss (WL), colour change, lignin degradation, and mechanical properties. Acetylation was carried out using two different reaction times to achieve weight percent gains (WPG) of around 7% and 10%. Understanding of the effect of acetylation and subsequent weathering on mechanical properties was enabled by analysing wood chemistry with Fourier transform infrared (FTIR) analysis and Raman spectroscopy. The mechanical tests of weathered unmodified and acetylated rubber wood revealed a decrease of tensile stiffness of the unmodified samples as a function of weathering time, while stiffness was retained for the acetylated samples. Weathered unmodified samples showed a bi-phasic stress-strain pattern with a high strain at breakage indicating a slippage of fibres under stress due to degradation of the middle lamella. This was hardly visible for acetylated samples. Thus, acetylation was shown to be effective for protecting rubber wood used in outdoor conditions.

Quasi-static and fatigue performance of bonded acetylated rubberwood (Hevea brasiliensis, Müll. Arg.)

“…The equilibrium moisture content of rubberwood at 65% RH/20 °C was reduced from about 11% to about 5.8%. Similar values have previously been reported for acetylated rubberwood for similar WPG (Olaniran et al 2019). In the following, the effects of acetylation of rubberwood on TSS and WFP of respective adhesives is examined.…”

“…06.59308° N, Long. 004.89078° E), shipped to Switzerland and further processed as described in Olaniran et al (2019). By the time of harvesting one tree (April 2017), the trees of the plantation were well over 30 years old and latex production had ceased.…”

“…The procedure for acetylation in this study was reported in a previous study (Olaniran et al 2019). Prior to chemical modification, the individual rubberwood samples were oven-dried at 103 °C for 24 h until a constant weight was achieved.…”

“…Rubberwood has been classified into durability class 4 (EN350:2016 2016) as mentioned in Wagenführ (2007).The durability issue has previously been tackled by acetylation (Chauhan et al 2001;Hassan et al 2017;Hisham et al 2018). However, the effect of acetylation on mechanical properties of rubberwood has only been investigated in a previous study by Olaniran et al (2019). It was shown that acetylation is a valuable treatment for outdoor use of rubberwood, as it slows down the impact of weathering on the mechanical properties of rubberwood.…”

Hyperspectral imaging and chemometrics reveal wood acetylation on different spatial scales

“…The loading vector showed corresponding positive bands at 2940 cm -1 and 1660 cm -1 due to the C-H stretch of O-CH 3 groups and the C=O of acetyl groups previously observed in the Raman spectra of acetylated lignin [37]. The loading also includes a positive band at 1725 cm -1 , which was likely due to the carbonyl stretching of acetyl groups previously reported for acetylated lignin and wood [37,38]. The fourth component explained 5% of the remaining data variation and mainly illustrated the outer layers of the cell walls based on a strong contribution from the orientation sensitive cellulose band at 1090 cm -1 [39].…”