Effects of process conditions on physicomechanical, creep and biodegradable properties of bamboo–polylactic acid composites

本研究利用桂竹（Phyllostachys makinoi）加工廢料、原生型聚乳酸（Virgin polylactic acid，vPLA）、回收型聚乳酸（Recycled polylactic acid，rPLA）及回收型高密度聚乙烯（Recycled high density polyethylene，rHDPE）製備竹材塑膠複合材（Bamboo–plastic composite，BPC）。同時，利用萬能強度試驗機、動態機械分析儀、示差掃描熱分析儀、掃描式電子顯微鏡、色差計等儀器，探討竹粒片尺寸、竹粒片添加量、生物性潤滑劑添加量、熱壓溫度、冷卻速率及單板層積等對複合材各項物理性質、機械性質、熱性質及生物降解性質之影響。試驗結果顯示，利用竹粒片尺寸-6+16 mesh所製備之BPCvPLA，具有最佳之抗彎強度及最小的吸水率。此外，於vPLA基質中添加竹粒片，可提升其抗拉彈性模數及橡膠態區之儲存模數。而添加適量的生物性潤滑劑（2–4 wt%）則可增加BPCvPLA耐水性、尺寸安定性以及儲存模數。另外，抗彎強度、抗彎彈性模數及儲存模數均隨熱壓溫度升高而增加，顯示較高之熱壓溫度有助於提升BPCvPLA之抗彎性質及黏彈性質。再者，BPCvPLA之吸水率隨著密度增加而減少，其抗彎強度及抗彎彈性模數則隨著密度的增加而增加；其中，密度900 kg/m3者具有最佳之抗彎強度（42.4 MPa）及抗彎彈性模數（4.1 GPa）。而利用單板層積所製備之BPCvPLA板心合板（BPC core plywood，BPCP），相較於BPCvPLA（900 kg/m3）可提升約2.3倍之抗彎強度，而抗彎彈性模數約可提高2.0倍，顯示單板層積確實有助於提升BPCvPLA之機械性質。 此外，在生物降解性質方面，由BPCrPLA之質量損失率試驗結果得知，以密度500 kg/m3者之損失率最大，經360 d土壤掩埋試驗後，其質量損失率達44%，此現象與複合材吸水率具相關性。在PLA基質數量平均分子量（Mn）方面，不同密度BPCrPLA之Mn均隨著降解時間增加而減少。其中，密度700 kg/m3之BPCrPLA經360 d的掩埋後，Mn由42 kg/mol下降至約16 kg/mol，顯示rPLA經土壤掩埋試驗後能有效地降解。 而在潛變性質方面，透過時間–溫度疊加原理（Time-temperature superposition principle，TTSP）之短期加速潛變試驗模式，可有效預測BPCvPLA長時間潛變行為及使用年限。於vPLA中添加40 wt%竹粒片製備之複合材，於試材10%平均破壞載重（Average breaking load，ABL）下，其使用年限較vPLA延長約3.5倍時間。In this study, Makino bamboo (Phyllostachys makinoi) residue, virgin polylactic acid (vPLA), recycled polylactic acid (rPLA) and recycled high density polyethylene (rHDPE) were used as raw materials to manufacture bamboo–plastic composite (BPC). Effects of bamboo particle size, bamboo particle content, bio-based lubricant, hot-press temperature, cooling rate and laminated veneer on physicomechanical, thermal and biodegradable properties of BPC were evaluated by universal testing machine, dynamic mechanical analyzer (DMA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and color difference meter, etc. These results showed that the BPCvPLA with bamboo particle of -6+16 mesh exhibited the strongest modulus of rupture (MOR) and the lowest water absorption. In addition, the tensile modulus and storage modulus (rubbery plateau) were significantly improved when the vPLA reinforced with bamboo particle. On the other hand, the water absorption resistance, dimensional stability and storage modulus of BPCvPLA could be increased by adding the bio-based lubricant at weight fraction of 2–4 wt%. Moreover, the MOR, modulus of elasticity (MOE) and storage modulus increased with press temperature increasing. It is indicated that the flexural and viscoelastic properties of BPCvPLA can be improved at higher press temperature. In addition, the water absorption of BPCvPLA decreased and the MOR and MOE of BPCvPLA increased with increasing composite density. The BPCrPLA with a density of 900 kg/m3 exhibited the strongest MOR (42.4 MPa) and MOE (4.1 GPa). On the other hand, the BPCvPLA core plywood (BPCP) with a density of 900 kg/m3 can be 2.3-fold enhancement in MOR and 2.0-fold enhancement in MOE of BPCvPLA with a density of 900 kg/m3, respectively. This result demonstrated that the manufacture technology of laminated veneer can improve the mechanical property of BPCvPLA. After 360 d of burial soil test, the BPCrPLA with a density of 500 kg/m3 exhibited the highest mass loss (44%). This phenomenon may be correlated with water absorption behavior of composites. Regardless of BPCrPLA density, the number-average molecular weight (Mn) of PLA matrix in BPCrPLA decreased with increasing degradation time. As an example of the BPCrPLA with a density of 700 kg/m3, the Mn decreased from original 42 to 16 kg/mol after 360 d of burial soil test. This result indicated that rPLA can be degraded effectively undergoing burial soil test. The time-temperature superposition principle (TTSP), a short-term and acceleration creep test, can be simulated or predicted long-term creep behavior and lifetime of BPCvPLA. Accordingly, the lifetime of BPCvPLA with 40 wt% bamboo particles at 10% average breaking load (ABL) was extended to 3.5 times as compared to the vPLA.摘要 i Abstract iii 目錄 v 表目次 vii 圖目次 ix 第一章 前言 1 第二章 文獻回顧 4 一、竹林分布與竹材應用 4 二、製程條件對塑膠複合材性質之影響 6 三、聚乳酸複合材之介紹 10 四、生物可分解型塑膠複合材之生物降解性質 13 五、時間–溫度疊加之理論基礎 16 第三章 材料與方法 20 一、試驗材料 20 二、複合材製備及試驗方法 21 三、性質分析 24 第四章 結果與討論 32 一、竹粒片尺寸對BPC性質之影響 32 （一）竹粒片尺寸對BPC物理性質之影響 32 （二）竹粒片尺寸對BPC機械性質之影響 33 （三）竹粒片尺寸對BPC黏彈性質之影響 36 二、竹粒片含量對BPC性質之影響 39 （一）竹粒片含量對BPC物理性質之影響 39 （二）竹粒片含量對BPC機械性質之影響 40 （三）竹粒片含量對BPC黏彈性質之影響 43 三、生物性潤滑劑添加比例對BPC性質之影響 46 （一）生物性潤滑劑添加比例對BPC物理性質之影響 46 （二）生物性潤滑劑添加比例對BPC機械性質之影響 47 （三）生物性潤滑劑添加比例對BPC黏彈性質之影響 50 四、熱壓條件對BPC性質之影響 52 （一）熱壓條件對BPC吸水率及吸水厚度膨脹率之影響 52 （二）熱壓條件對BPC結晶性質及機械性質之影響 55 （三）熱壓條件對BPC黏彈性質之影響 58 （四）冷卻速率對BPC內部構造之影響 60 五、密度及單板層積對BPC性質之影響 61 （一）密度及單板層積對BPC物理性質之影響 61 （二）密度及單板層積對BPC機械性質之影響 66 （三）密度及單板層積對BPC生物降解性質之影響 69 六、以時間–溫度疊加原理預測BPC之使用年限 85 第五章 結論 94 參考文獻 9