針葉樹構造用合板の製造プロセスにおける配分方法の違いが製品の温室効果ガス排出量に与える影響

抄録

The manufacture of softwood plywood does not vary greatly from product to product, and allocation of greenhouse gas (GHG) emissions is often based on the lumber volume of the finished product. However, since products of the same thickness may be characterized by different numbers of veneer layers, an allocation method that considers this may be more appropriate.

Therefore, to evaluate the GHG emissions involved in manufacturing plywood products, this study allocated energy and other inputs to the product-manufacturing process according to the number of layers of veneer. To assess the impact of the allocation method on GHG emissions, the results were compared with those of an allocation method based on the lumber volume of the product. Four products were evaluated: 9-mm-thick × 5 veneer layers, 12-mm-thick × 5 veneer layers, 24-mm-thick × 7 veneer layers, and 28-mm-thick × 9 veneer layers. The system was bound by the raw material procurement and product-manufacturing stages.

The allocation method based on the number of layers showed a 1.44-fold difference in GHG emissions per m3 of product between the product with the highest GHG emissions (9-mm-thick × 5 veneer layers) and that with the smallest thickness (24-mm-thick × 7 veneer layers). This difference was influenced by the number of veneer layers per unit thickness. In comparison, the allocation method based on product volume resulted in a 1.11-fold difference in GHG emissions between the product with the greatest emissions (9-mm-thick × 5 veneer layers) and that with the smallest thickness (24-mm-thick × 7 veneer layers). This difference was influenced by differences in the amounts of adhesive used. Comparing the impact of the different allocation methods, the difference in GHG emissions was greatest for the 24-mm-thick × 7-veneer-layers product, with the result of the allocation method that considered the number of layers being 0.87 times greater than that based on the amount of lumber in the product. This difference indicates that the number of layers per unit has a greater impact on GHG emissions than the lumber volume of the finished product.

In summary, it is clarifying that different allocation methods for the manufacturing process have different impacts on the GHG emissions of the product. Therefore, for allocation in the plywood manufacturing process, the number of layers per unit thickness of veneer should be considered.