定向竹重組板材製造及其性能評估

Abstract

本研究選取臺灣及中國竹材加工業市場廣泛使用之孟宗竹（Phyllostachys pubescens）及臺灣桂竹（P. makinoi）進行定向竹重組板材（Oriented bamboo scrimber board，OBSB）製造及其性能評估，除探討去竹皮加工（Epidermis-peeling treatment，EPT）及蒸汽熱處理（Steam-heating treatment，SHT）對於各項基本性質及製成OBSB後之影響外，亦比較不同組合型式之竹木混合板材（Bamboo-wood composites，BWC）與OBSB性質差異。再者，利用無甲醛相思樹皮單寧膠（AcBTanGlu），評估與酚甲醛（PF）、脲素甲醛（UF）樹酯所製作OBSB性質之差異，另將OBSB以三層型式製成直交式集成OBSB板材（Cross laminated-OBSB，CL-OBSB），評估不同組合比例之CL-OBSB各項性能。試驗結果顯示，孟宗竹及桂竹經EPT及SHT後將提升半纖維素、抽出成分及灰分的百分比含量，而全纖維素及α-纖維素的含量百分比則降低，各竹材經SHT後之木質素含量並無明顯差異。未去皮竹材呈現較大的抗彎彈性模數（MOE）及抗彎強度（MOR）值，經SHT之後，MOE及MOR值均下降，當竹材經過EPT後則會提升吸水率（WA%），而SHT將降低竹材的吸水性。再者，評估中國產（C-OBSB）及臺灣產（T-OBSB）二種孟宗竹所製造之OBSB各項性質的結果顯示，超音波傳遞速度（Vu）、MOE、MOR值及內聚強度（IB）值均與板材密度呈正比關係，且T-OBSB之Vu (//)、MOE、MOR值及IB值亦明顯較C-OBSB高，Vu (┴)顯示較木理方向低，而以T1.0B的MOR值最大（172.88 MPa）。 此外，評估八種OBSB竹材之各項性質顯示含竹皮經蒸汽熱處理桂竹（TPmE-H）製成OBSB的 Vu (//)及動彈性模數(//)（DMOE(//)）最高，而以CMoso-H最低，竹材經SHT後再製成OBSB時，其Vu (//)及DMOEu (//)均無顯著差異（p > 0.05）；至於垂直木理方向之Vu (┴) 及DMOEu (┴)則較平行木理方向低。由MOE (//)及MOR (//)值均顯示TPmE-H經SHT後可獲最大值（分別為19.58 GPa及196.50 MPa）。此外，竹材經SHT的回彈率（SB）較低，由TMoso製成OBSB之 IB值（3.04 N/mm2）最高。其TMoso-H可獲207.83 kgf最大的木螺釘保持力（SHS）值。竹材經SHT後製成OBSB之吸水率（WA%）、體積膨脹率（S%）及厚度膨脹率（TS%）均明顯下降，顯示尺寸安定性獲得改善。BWC方面的Vu及打音音速值（Vt）以GroupⅡ（全竹廢料）最高，MOE、MOR及SHS值則顯示GroupⅤ（竹/木/竹=1：2：1）可獲最大的值。WA%值與竹廢料含量呈正比關係，而TS%則呈現反比情形，又因邊皮材廢料的半纖維素含量較廢竹材料高，因此廢竹材比例與TS%及S均呈反比關係。利用桂竹及PF膠製成OBSB，其Vu (//) 、Vt (//)、DMOEu (//) 及DMOEt (//)值均顯著地較孟宗竹及UF膠高，桂竹及孟宗竹製成OBSB後同樣為DMOEu值 > DMOEt值 > MOE值。當桂竹經SHT後並配合PF膠合劑製成OBSB時可獲最大的MOR值（210.5 MPa），而桂竹及孟宗竹經SHT後可降低OBSB之WA%、TS%及S%值，亦可提升OBSB尺寸安定性。 再者，AcBTanGlu之聚酚類經13C核磁共振分析儀（13C NMR）及散反射式傅立葉轉換紅外線光譜儀（DRIFT）圖譜分析得知富含酚類化合物及類黃酮鍵結組成之B型縮合單寧。由六叉極化魔角旋轉（CP/MAS）13C-NMR圖譜得知其縮合單寧可與六亞甲基四胺形成網狀結構之高分子化合物，由GC-MS分析顯示未出現甲醛的訊號，經熱重分析得知具良好熱穩定性且未影響原竹材之化學官能基特性。當AcBTanGlu混合2%六亞甲基四胺，於150 oC熱壓溫度下持續15 min所壓製成的OBSB可獲最大的膠合剪斷強度。AcBTanGlu做為OBSB膠合劑後之Vt、Vu、DMOEu、DMOEt、SHS、尺寸安定性均較UF及PF膠合者高，經白腐菌（L. b.）及褐腐菌（L. s.）耐腐朽試驗後顯示具良好的耐腐朽性。OBSB製成CL-OBSB三層結構材料，平行方向之Vu、DMOEu、Vt及DMOE值與明顯地較垂直方向測值高，其中以Type Ⅲ（2：1：2）將可獲得最大的Vu (//) 值，由於Type Ⅲ平行木理方向之竹條佔80%，故MOE、MOR及壓縮強度（C）值均顯示最大。利用PF做為CL-OBSB材料時之膠合剪斷強度顯示S//值僅為S┴值1.03倍及可獲得卓著的膠合剪斷強度及尺寸安定性。

Moso bamboo (Phyllostachys pubescens) and makino bamboo (P. makinoi) are important economic bamboo species in Taiwan and China. This research evaluated the effects of epidermis-peeling (EPT) and steam-heating (SHT) treatments on basic properties of these two bamboo culms and oriented bamboo scrimber board (OBSB) made from them. Comparison was also made between species from Taiwan and China. Moreover, OBSB was compared against bamboo-wood composites (BWC) made using coniferous slabwood and makino bamboo residue of various proportions to explore their differences in properties. Furthermore, OBSB was manufactured using different adhesives including phenol formaldehyde (PF) resin, water-soluble urea formaldehyde (UF) resin and glue made of tannin extracted from Acacia bark (AcBTanGlu) to determine their impact on OBSB properties. Finally, cross-laminated OBSB (CL-OBSB) was processed using layers of OBSB in different orientations to examine the differences in performance. Significant results obtained are summarized that EPT and SHT changed the chemical and mechanical properties of moso and makino bamboo culms from both Taiwan and China. In terms of chemical properties, the amounts of extractives and ash were increased after EPT and SHT in both moso and makino bamboos. In contrast, the contents of holocellulose and α-cellulose were decreased after EPT and SHT for the two bamboos. Steam-heated moso bamboo collected from China contained the lowest cellulose content but the highest amount of hemicellulose. The contents of lignin whose structure was not destroyed at 120oC showed no significant difference after SHT. As for mechanical properties, the density of all makino and moso bamboo samples were reduced after SHT. Moreover, the trend of decrease in density was similar to that of reduction in holocellulose, α-cellulose, hemicellulose, and equilibrium moisture contents. All bamboo samples with epidermis intact presented the highest modulus of elasticity (MOE) and modulus of rupture (MOR) whether steam-heated or not. Epidermal integrity contributed to dimensional stability of the bamboo. Both MOE and MOR of all bamboo samples were decreased after SHT. The water absorption (WA%) ability was increased after EPT but decreased after SHT. Besides, OBSB made using moso bamboo grown in Taiwan (T-OBSB) and China (C-OBSB) was examined using non-destructive techniques (NDT). Ultrasonic-wave velocity (Vu) measurements were obtained at three density levels (0.8, 0.9, and 1.0 g/cm3) and the dynamic modulus of elasticity (DMOEu) was calculated. Moreover, static MOE, MOR, profile density distribution, internal bond strength (IB), springback (SB), and dimensional stability were determined using traditional methods. Positive linear relationships between density and Vu, DMOEu, MOE, and MOR were observed for measurements parallel (//) or perpendicular (┴) to fiber direction of the OBSB. Moreover, Vu(//), MOEu(//), MOE(//), and MOR(//) were higher than Vu(┴), DMOEu(┴), MOE(┴), and MOR(┴). C-OBSB had slightly lower Vu(//), Vu(┴), DMOEu(//) and DMOEu(┴) than T-OBSB. On the other hand, T-OBSB had higher MOE(//), MOE(┴), and MOR(//) than C-OBSB, but lower MOR(┴). The profile density distribution of high-density T-OBSB showed significant data scattering. The profile density distribution of C-OBSB was homogeneous at all density levels. IB and SB data were directly proportional to density, but WA%, thickness swelling (TS%), and volumetric swelling (S%) were inversely proportional to density. T-OBSB has better bonding, strength and dimensional stability than C-OBSB. BWC made using makino bamboo residue alone was found to have the highest Vu and Vt. In terms of strength properties, BWC made with bamboo/wood/bamboo at 1:2:1 ratio exhibited the maximum MOE, MOR, and SHS. Moreover, WA% was positively correlated with while TS% was inversely related to the proportion of bamboo residue in BWC samples. When OBSB made using makino bamboo strips and PF resin showed significantly higher Vu (//), Vt (//), DMOEu (//) and DMOEt (//) than that made using moso bamboo strips and UF resin. Moreover, SHT and use of PF resin as adhesive in the processing contributed to achieve highest MOR of 210.5 MPa. OBSB made using either makino or moso bamboo strips presented the same trend of DMOEu > DMOEt > MOE. Moreover, higher MOR was observed in OBSB made using moso bamboo strips. OBSB made using steam-heated makino and moso bamboo had lower WA%, TS% and S%, thus enhancing its dimensional stability. When glue made from AcBTanGlu examined using 13C NMR and DRIFT analysis revealed B-type condensed tannins rich in phenolic compounds and flavonoid bonds. CP / MAS 13C-NMR spectrum also showed that the condensed tannins could form a network of polymer compounds with hexamethylenetetramine. Analysis by GC-MS revealed no formaldehyde signal, while thermogravimetric analysis showed good thermal stability and insignificant effect on chemical properties of the original bamboo material. Mixing AcBTanGlu with 2% hexamethylenetetramine, followed by hot pressing at 150°C for 15 min resulted in maximum gluing strength for OBSB. Using AcBTanGlu as adhesive for processing OBSB contributed to higher Vt, Vu, DMOEu, DMOEt, SHS and dimensional stability than using PF and UF. Moreover, OBSB glued with AcBTanGlu showed good decay resistance. At last, CL-OBSB made using three layers of OBSB in different orientations revealed that Vu, DMOEu, Vt, and DMOE were significantly higher in CL-OBSB made with bamboo layered in parallel than in perpendicular direction. Maximum Vu (//), MOE, MOR, and compression strength was observed in CL-OBSB made with 80% of bamboo strips layered in parallel direction. Shear strength analysis on CL-OBSB made using PF resin as adhesive showed S// only 1.03 times that of S┴ and exhibited excellent gluing strength and dimensional stability.