The influence of the green timber moisture content on the bending strength of the lengthwise glued pine cladding board | Svaigi zāģētas koksnes mitruma ietekme uz garumā līmētu priedes koksnes apdares dēļu robežstiprību liecē
2009
Iejavs, J., Latvia Univ. of Agriculture, Jelgava (Latvia). Forest Faculty. Dept. of Wood Processing
Finger jointing of green timber makes possible an efficient production of value-added wood. Green gluing is a new production method for established wood based products. In the conventional gluing process, when gluing dry wood, the first step is to dry the wood material to correct moisture content to achieve necessary properties of the wood. Normal wood moisture content will be in the range from 5% to 18%. In the green gluing technology the moisture content of the wood will be higher than fibre saturation point and it may vary a lot. Green gluing is applied on the wood material at early stage in the production process, before a lot of work has been invested in the material. This leads to a reduction of the cost of raw material. No need to dry the waste as it is eliminated before drying, reduced energy consumption and with improved value of the waste material. The present research evaluates finger jointing of green European pine (Pinus sylvestris L.) timber with two adhesive systems in five variations: one-component structural polyurethane (Purbond HB 440); one-component non structural polyurethane (Bostik XPU 18268 F); two component phenol resorcinol formaldehyde with soy protein (Prefere 4030\\SI-300 and Prefere 4030\\SIPC-500) and two-component phenol resorcinol formaldehyde with casein protein (Prefere 4030\\C80). The aim of the research: to investigate the influence of the pine wood moisture content on green glued pine cladding board critical bending strength after drying. The samples have been made according to standard cladding processing and finger jointing technology, but with diverse adhesive system application. 4-point critical bending strength according to LVS EN 408, moisture content and density before gluing and after drying were evaluated. In total were tested 100 specimens 20 for each adhesive system and adhesive combination. For statistical analysis were used standard MS Excel and SPSS soft ware. Both adhesive systems (polyurethane and two-component phenol resorcinol formaldehyde with soy ore casein protein) obtain necessary critical bending strength for producing cladding boards. After drying process, phenol resorcinol formaldehyde combination systems have 30% higher average critical bending strength than polyurethane systems. Several European Union countries collaborate in the COST action E34 to work out the core document ''Green gluing of wood'' for structural application. That will open up new opportunities upon both structural and non-structural gluing of green wood and will increase the efficiency of the glue-lam producing process.
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