Citric acid as a green binder for particleboard fabricated from oil palm biomass

Owing to its natural adhesivity, citric acid (CA) could serve as a promising natural-based adhesive to replace the petroleum-based urea formaldehyde (UF) resin for bonding wood and wood-based composites. In this study, the performance of CA with the addition of tapioca starch in various ratios was evaluated as a green binder for oil palm biomasses particleboard production. The objectives of the study were to investigate the effects of starch addition on the performance of CA-bonded oil palm biomasses particleboard in terms of physical, mechanical, formaldehyde emission and biological properties. Three CA/starch ratios (100:0, 87.5:12:5, and 75:25) were used as a binder for particleboard to bond three types of oil palm biomasses, namely oil palm trunk (OPT), oil palm frond (OPF) and empty fruit bunch (EFB). CA and starch at different mixing rations were dissolved in distilled water to attain adhesive solutions with 60% solid content. 20 wt% adhesive level were sprayed on the particles of oil palm biomasses. The sprayed particles were then dried in an industrial oven at 60 °C for 12 h prior to hot pressing. The partially dried particles were then subjected to hot pressing at 180 °C for 10 min. A set of control particleboards using 10 wt% UF resin level was produced for comparison purposes. The mechanical, physical, formaldehyde emission, and biological properties of the particleboards as function of CA/starch rations were evaluated in accordance with JIS A 5908 (2003), JIS A 1460 (2001) and AWPA E10-16 (2020) standard test methods, respectively. Statistical Analysis System (SAS) were used to further compare the mean between each variable using two-way ANOVA analysis. The results revealed that, as a dimensionally instable adhesive, UF-bonded particleboard showed very high thickness swelling (TS) values (59.96 to 144.02%) after being soaked in water for 24 h. Meanwhile, The TS values of OPF, OPT, and EFB particleboards bonded with pure CA (100:0) were approximately one-sixth, one-fifth, and one-seventh of their respective UF counterparts. However, starch addition increased the TS values of the particleboard due to the starch solubility in water. Similarly, the water absorption (WA) of the particleboard increased when 25% starch was added to the CA solution. The results of cyclic aging treatment revealed that UF-bonded particleboard failed to withstand the treatment under severe conditions and disintegrated during aging treatment. Meanwhile, CA-bonded particleboard displayed superior dimensional stability and maintained its original shape after the cyclic aging treatment. However, the dimensional stability of the particleboards deteriorated as a higher ratio of starch was added. As for mechanical strength, all CA-bonded particleboards displayed superior performance compared to that of UF-bonded particleboard. Some of the particleboard displayed better bending strength when bonded with a mixture of CA and tapioca starch at ratio of 87.5:12.5. Although some particleboards showed a decreasing trend after an addition of 12.5% starch, the decrement was, however, insignificant compared to those bonded with pure CA. The addition of 25% starch was unfavorable as it resulted in an adverse effect on the mechanical properties of the particleboard. Decay resistance against white rot fungi and termites of both UF- and CA-bonded particleboards indicated that the CA could protect the wood from decay owing to its acidic nature. Addition of starch slightly increased the weight loss of the samples against white rot fungi and termites. More importantly, the formaldehyde emission of CA-bonded particleboard is very low compared to that of UF-bonded particleboard. The effect of starch addition on the formaldehyde emission is insignificant. Overall, the addition of 12.5% starch could be beneficial to the physical and mechanical properties of the oil palm biomasses particleboard. But the addition of 25% starch was unfavorable as it resulted in an adverse effect on the mechanical properties of the particleboard. In conclusion, this study demonstrated that CA and starch could be used as a green binder for bonding oil palm biomasses particleboards.

Text 121182.pdf Download (1MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18549

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