Evaluating the influence of CCA and DOT wood preservative treatments on one component laminated P. patula polyurethane bond performance
Date
2021-03
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: With the increasing movement towards environmentally friendly and sustainable building materials in the construction industry, engineered wood products have become a preferred structural material. However, the adoption of engineered wood products as a building material could be curtailed by failure to identity and eliminate threats,such as biodeterioration agents(e.g. fungus, insects). Wood preservation offers the opportunity to improve wood resistance and increase product service,through the impregnation of wood preservative chemicals into the wood cell lumen and walls.Some engineered wood products are too large to be treated after manufacturing, which necessitates treatment before adhesive bonding of laminates. In other cases treatment before adhesion is preferable from a process and chemical retention perspective. However, the metallic and inorganic salt deposits of the preservatives may present complications,as they can interfere with bond formation between the wood substrates and adhesive. The interference of these deposits may lead to poor bond strength and durability and could lead to product failure and not meeting the standard requirements.
This research involved evaluating popular wood preservation treatments on the bond line performance of Pinus patula wood bonded with a one-component polyurethane (PUR) adhesive. The specific objectives of the experimental study were as follows:•Evaluate the effects of chromium copper arsenic(CCA)and disodium octaborate tetrahydrate (DOT) wood preservatives and Pinus patula wood properties (density, sapwood/heartwood) on the bond performance of one component polyurethane bonded laminates;•Evaluate the influence of wood properties of Pinus patula (sapwood, heartwood, and density) on retention rate.The experimental design consisted of four factors (treatment chemical, concentration, wood density and sapwood/heartwood ratio). The treatment chemicals had different treatment levels: CCA (2% and 4%concentration),DOT(1.67% and 3.30%concentration)and an untreated control. The density had two levels -lower than 462 kg/m3and higher than 473 kg/m3and the wood type was separated into two levels,sapwood only specimens and specimens with more than 35% heartwood. In total, the experimental study had 20 groups which were tested for bond shear strength and delamination.To realise the objectives of the experimental research, the wood impregnation process was adopted from SANS 10005 (2016), whilst the material specifications and laminate manufacturing procedures were adopted from SANS 10183-4-2 (2009) and ASTM D905 (2008). The performance of the PUR adhesive bonds was evaluated and measured through standardised test methods including shear strength, wood failure percentage and resistance to delamination by accelerated exposure.
produced higher shear strength. However, one of the unexpected findings was that in most cases heartwood specimens showed a higher shear strength (whether treated with CCA or DOT or untreated) in comparison to sapwood.In terms ofbond durability, all the treated and untreated (control) test blocks met the requirementsof EN 14080 (2013), as the average total delamination did not exceed 10% in length (mm)in any of the groups. Overall, the DOT treated samples were found to have abetter resistance to delamination in comparison to CCA treated samples. The results also indicated that with increasing concentration levels of CCA, delamination increased.
With regards to the effect of wood properties on retention rate, the results showed that sapwood had a higher retention capacity than heartwood for both preservatives (CCA andDOT).Density was also found to have a significant effect on retentionwiththe retention rate beingmuch lower in most high-density wood samples when compared to low density-wood samples. Such findings highlight the importance of understanding the treatability behaviour/response of various parts of wood (e.g. sapwood, heartwood), anatomical characteristics (e.g. thick or thin cells walls) and size, in order to ensure the required or targeted retention and penetration is achieved during treatment.Overall, the shear strength,wood failure and delamination results suggested that engineered wood products canbe produced from CCA and DOTtreated Pinus patula.However, the concentration levels should be carefully selected, as the study found that with increasing concentration levels, delamination also increased.
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
Description
Thesis (MSc)--Stellenbosch University, 2021.
Keywords
Heartwood, UCTD, Pinus patula, Engineered wood industry, Strength of materials, Composite materials -- Delamination