Some physical and mechanical properties of cross-laminated timber panels produced from heat treated wood

In the study, some physical and mechanical properties of different types of cross laminated timber (CLT) panels produced from different types of wood with and without heat treatment application with the ThermoWood method were determined. In addition, the effect of heat treatment on the adhesion strength of polyurethane (PU) glue and the use of wood species such as poplar (Populus spp.), which is less used as timber, in the middle layer of CLT panel production were investigated. In the production of CLT panels, heat treated Scotch pine (Pinus sylvestris L.) and American ash (Fraxinus americana) timbers and non-heat treated Scotch pine and American ash timbers were provided by Nova company. The Samsun poplar (I-77/51 Populus deltoides Bartr.) wood without heat treatment was provided by Kaswood company. The type of wood material used in the layers in the production of CLT panels was applied in three different ways. The first of these; S 90, TS 90, D 90 and TD 90 group panels produced using scotch pine, thermo scotch pine, ash and thermo ash in the outer layers in one by one groups, poplar wood was used in the middle layer of all groups. The second K 90 group panels produced using only poplar wood in the outer layers and middle layer. Finaly compared to the groups whose middle layer is produced at a 90 degree angle, the S 45, TS 45, K 45, D 45 and TD 45 group panels were produced with the middle layer angle orientation set to 45 degrees againist the outher layers. Test samples were prepared from the produced CLT panels and the wood materials used for producing the CLT panels according to the dimensions specified in the relevant standards. The data obtained as a result of the study were evaluated by applying multiple variance analysis with the help of SPSS 26 statistical program and the results were interpreted. As a result of the study, it was observed that the heat treatment application caused a decrease in the fiber saturation point, equilibrium moisture content, swelling, bending strength, tensile strength, adhesion strength values of the wood materials used in production, and generally an increase in the percentage of extractive contend of the wood materials. In addition, an increase in the modulus of elasticity and compressive strength values of the materials was determined. When the properties of the produced CLT panels were examined, it was seen that the heat treatment application provided a decrease in the thickness swelling percentages of the panels and a small decrease in the water absorbtion percentages of the panels, while the middle layer angle orientation was not effective on the thickness swelling percentage, but it had a slight increasing effect on the water absorbtion percentages. In terms of the water vapor transmission rate of the panels; the heat treatment application caused a decrease in the S 90-45 and TS 90-45 groups, a low decrease in the D 90-45 and TD 90-45 groups and the middle layer angle orientation caused a low decrease in the other groups except the TD 90-45 group. It was observed that the heat treatment application caused a decrease in the thermal conductivity properties of the panels, also the middle layer angle orientation caused a decrease in the values of TS 45, K 45, D 45 ve TD 45 groups. The heat treatment application caused a decrease in the bending strength and modulus of elasticity values of the panels. The middle layer angle orientation caused an increase in these values against the S 90, TS 90, K 90, D 90 and TD 90 group values in the TS 45, D 45 and TD 45 groups, and generally a decrease in these values in the S 45 and K 45. When the values are compared with the values specified in the ANSI APA PRG 320 (2012) CLT production standard, D 45 group provides E1 class, S 90, S 45, D 90 and TD 45 groups provide E3 class properties. TS 90-45, K 90-45 and TD 90 groups were not included in any class due to insufficient modulus of elasticity values. The heat treatment application had an increasing effect on the compressive strength of the panels parallel to the direction of the outher layers and panel surfaces in the S 90-45 groups and a decreasing effect in the D 90-45 groups. The middle layer angle orientation had a decreasing effect in the K 45 and D 45 group and an increasing effect in the S 45, TS 45 and TD 45 groups in terms of compressive strength. When the compressive strength values were compared with the ANSI APA PRG 320 (2012) CLT production standard, it has been observed that all groups meet the E1 class features. There was no statistically significant difference between the groups in the compressive strength properties perpendicular to the panel surfaces. The heat treatment application had an increasing effect on the delamination properties of the panels in the S 90-45 groups, but did not have any effect in the D 90-45 groups. The middle layer angle orientation provided an increase in the strength of the panels against water by reducing the delamination in the groups except the D 45 group. The middle layer angle orientation caused a significant difference in the 4-point bending strength, compressive strength parallel to the direction of the outher layers, delamination properties and thickness swelling of the panels, and although the middle layer angle orientation caused a small difference in the other properties, it could not provide a significant difference in the 95% confidence interval. As a result of the study, new studies are carried out using native or endemic wood species in panel production, determining the suitability of different hardwood species in CLT panel production, determining the performance of CLT panels produced from different wood species in order to determine the effects of 45 degree angle orientation application in the middle layer, determine the performances of different types of glue and brands, to carry out new studies by using different wood species in successive layers in panel production, and to carry out extensive studies on more durable joint types as an alternative to finger joint connections.