Today, most wood adhesives are prepared from fossil-based polymers and contain hazardous components, e.g., formaldehyde. With the growing environmental concern there is an urge to develop biobased and harmless substitutes....

Today, the most commonly used adhesives in the wood industry are fossil-based, but the search for new, renewable and less hazardous, resources for adhesives is intensifying. Hemicelluloses show promising bonding performance when used as a component in wood adhesives. Since batch-to-batch variations can affect the use of hemicelluloses in a large-scale production, we have investigated the effect of hemicellulose molecular weight on important adhesive properties, such as viscosity and bond strength, by using locust bean gum as a hemicellulose model and varying the molecular weight through hydrolysis. Results showed that there is a nonlinear proportionality between bond strength and molecular weight. In the molecular weight range used in the study, 70–1460 kDa, anoptimum in the adhesive performance was achieved with intermediate molecular weights, 320 and 530 kDa, especially when considering applicability and bond strength. Adhesives with lower molecular weights, 70 and 150 kDa, did not exhibit sufficient cohesive strength; therefore, the bond strength was lower. The adhesive with higher molecular weight, 1460 kDa, was difficult to apply, especially since its maximum solid content was very low, 5 wt %.

The formaldehyde release and the formaldehyde content from the commercial particleboards were determined using the flask and perforator methods. Since the melamine faced boards were used in this research, the flask method was applied to evaluate how much the decorative surface (melamine impregnated paper) affects the test results in terms of reducing the formaldehyde emission from the samples. Hence, the flask method tests were performed simultaneously with one test series presenting the melamine faced samples, and the other one presenting the samples with sanded surface. Also, the decorative surface was sanded off from all of the test samples intended for formaldehyde content measurements using perforator method. During this research, it was found that by removing the decorative surface, the formaldehyde emission increased in the range from 12.6% to 16.6%, suggesting that the decorative surface acts as a barrier to formaldehyde emission even for the samples of such a small size used in the flask method. In addition, very high correlation, of 0,989 and 0,959, was found between the formaldehyde content values (perforator method) and the values of formaldehyde release from sanded and melamine faced samples, respectively.