多元醇液化竹材與異氰酸酯所製備聚胺基甲酸酯樹脂之膠化時間及木材膠合強度

Gelation time and wood bonding strength of polyurethane resins prepared with polyhydric alcohol liquefi ed bamboo and isocyanate

本研究將孟宗竹（Phyllostachys heterocycla；Moso bamboo）、麻竹（Denrdrocalamus latifl orus；Ma bamboo）及桂竹（Phyllostachys makinoi；Makino bamboo）於聚乙二醇／丙三醇混合液中以硫酸為催化劑進行液化處理，所得液化竹材分別與PMDI、Desmodur L及Desmodur N等三種異氰酸酯混合製備聚胺基甲酸酯樹脂（Polyurethane resins；PU）。探討不同液化竹材、異氰酸酯及NCO/ （OH+COOH）莫耳比（R值）所調配PU樹脂之膠化時間、樹脂薄膜之機械性質及木材膠合強度。試驗結果顯示，液化竹材與異氰酸酯混合之PU樹脂具備常溫硬化性，其中以Desmodur L為異氰酸酯原料者有較適合加工應用之膠化速度，以PMDI為原料者則膠化速度過快而無法提供足夠的可使用時間，以Desmodur N為原料者則反應過慢，然添加催化劑可縮短其膠化時間。異氰酸酯種類及R值為影響PU薄膜拉伸性質之主要因素，以Desmodur L為原料者，其薄膜性質硬脆，拉伸強度及模數較大，破壞變形量則較小；而以Desmodur N為原料者則較為軟韌，其拉伸強度偏低，然在拉伸破壞前可容許較大之變形量；提高PU樹脂調配時之R值可使樹脂薄膜之拉伸強度、模數及破壞變形量增加。將此PU樹脂做為膠合劑而應用於木材膠合時，採用Desmodur L為原料之膠合性能優於採用 Desmodur N者。 Phyllostachys heterocycla (Moso bamboo), Denrdrocalamus latiflorus (Ma bamboo) and Phyllostachys makinoi (Makino bamboo) were liquefi ed in the mixture of polyethylene glycol/glycerol with H2SO4 as a catalyst. The liquefi ed bamboos were blended with three kinds of isocyanate, such as PMDI, Desmodur L and Desmodur N to prepare polyurethane resins (PU). The gelation time, mechanical properties of resin films and wood bonding strength of PU resins that prepared with different liquefied bamboos, isocyanates and NCO/(OH+COOH) molar ratios (R value) were investigated. The results show that PU resins prepared by mixing liquefied bamboo with isocyanate could set under room temperature. Among which, using Desmodur L as the raw material of isocyanate had a gelling speed more suitable for processing than others. However, the gelling speed for that used PMDI as the raw material was too fast to provide a suffi cient pot-life. On the other hand, the gelling speed was too slow for that used Desmodur N as the raw material, but its gelation time could be shortened by adding a catalyst. The kind of isocyanate and the R value were the main factors that infl uenced the tensile properties of PU fi lms. Using Desmodur L as the raw material formed fi lms with the properties of hard and brittle, which had higher tensile strength and modulus but had lower breaking deformation. While used Desmodur N as the raw material, the fi lms were more soft and toughness, which had low tensile strength but allowed a larger amount of deformation before the tensile damage occurred. The tensile strength, modulus and breaking deformation of fi lms could be increased by increasing the R value during the preparation of PU resin. When these PU resins was applied as an adhesive for bonding wood, using Desmodur L as the raw material could provide a better bonding performance than that with Desmodur N