多元醇液化木材製備聚胺基甲酸酯膠合劑及用於低密度粒片板之製造

Abstract

本研究將相思樹(Acacia confusa; Taiwan acacia)及杉木(Cunninghamia lanceolata; China fir)利用PEG-Glycerol混合液為液化藥劑，硫酸為催化劑進行液化處理，所得之液化木材與PMDI、Desmodur L、Desmodur N等三種異氰酸酯混合製備聚胺基甲酸酯(Polyurethane; PU)樹脂，探討液化木材樹種、異氰酸酯種類、NCO/(OH+COOH)莫耳比（R值）、界面活性劑、催化劑等對PU樹脂性質之影響，並進一步探討此PU樹脂應用於木材膠合劑及應用於低密度粒片板製造可行性。由結果可知，以液化木材為基質之PU樹脂具備常溫硬化性，其中以PMDI為原料者具有最短的膠化時間，以Desmodur N為原料者之膠化時間最長。隨PU樹脂R值增加其膠化時間延長，添加催化劑可縮短其膠化時間，界面活性劑影響則較小。耐溶劑試驗顯示此類PU樹脂具有良好之重量保留率，而以Desmodur N為原料者之重量保留率較高，隨R值增加其重量保留率提高。DSC熱分析顯示硬化成膜之PU樹脂在高溫下可進一步促進其架橋反應。由FT-IR分析顯示，液化木材與異氰酸酯之間會形成胺基甲酸酯之鍵結。PU樹脂之拉伸強度和膠合強度，以液化相思樹-Desmodur L為原料者為佳。隨R值提高，PU樹脂之膠合強度和拉伸強度增加。以液化木材-異氰酸酯作為結合劑而應用於低密度粒片板製造時，宜採用熱壓方式製板，添加催化劑可降低所需之熱壓溫度並縮短熱壓時間。以PMDI為異氰酸酯原料有較佳的粒片板內聚強度及尺寸安定性。提高液化木材-異氰酸酯之R值可增加所有粒片板之內聚強度及尺寸安定性。以PMDI和Desmodur L為原料之PU結合劑，增加發泡劑添加量，可提高其粒片板之內聚強度和尺寸安定性。以液化相思樹為原料之粒片板性質優於以液化杉木為原料者。低密度粒片板經單板貼面可有效提高其靜曲強度，並達CNS 2215號中8型粒片板之標準。

Taiwan acacia (Acacia confusa) and China fir (Cunninghamia lanceolata) wood were liquefied using PEG-glycerol co-solvent with H2SO4 as catalyst. In preparation of polyurethane (PU) resins, the liquefied woods were blended with three kinds of isocyanate, such as PMDI, Desmodur L and Desmodur N. The effects of liquefied wood species, isocyanates, NCO/ (OH+COOH) ratios (R ratios), surfactant and catalyst on the properties of PU resins were investigated. The feasibility of these PU resins for wood gluing and low density particleboard manufacturing were investigated. From the results, PU resins with liquefied woods as base ingredients could cure at room temperature. The gel time of PU resins prepared from PMDI was the shortest, but prepared from Desmodur N was the longest. The gel time extended as the R ratios increased, but shortened as catalyst added. The effect of surfactant on gel time was not obvious. Solvent resistance test showed high degree of weight retention for these PU resins, among which, PU resins made from Desmodur N had the highest retention rate, and it could be increased as the R ratio increased. DSC thermoanalysis showed that the cured PU films could undergo further cross-linking reaction at high temperature. FT-IR analysis showed that urethane bond had formed between liquefied woods and isocyanate. PU resins prepared from liquefied Taiwan acacia- Desmodur L had the best film tensile strength and wood bonding strength. As the R ratios increased, the tensile strength and bonding strength of all PU resins were increased. When the liquefied wood-isocyanate was used as the binder for the manufacturing of low density particleboard, processing with hot-pressing was necessary, but the hot-pressing temperature and time could be lowered and shortened if catalyst was added. Low density particleboard made with PMDI had higher internal bonding strength and better dimensional stability than with others isocyanates. When the R ratio of liquefied wood-isocyanate increased, the internal bonding strength and dimensional stability would be increase for all particleboards. Increasing the amount of foaming agent could improve the internal bonding strength and dimensional stability of low density particleboards made with the binders of PMDI and Desmodur L. The properties of particleboard made from liquefied Taiwan acacia were better than liquefied China fir. Veneer overlay could increase the bending strength of low density particleboard and reached the type 8 standard in CNS 2215.