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Development and Characterization of Biodegradable Plastic Pellets Based on PHBV/ PVA
response surface methodology
|摘要:||本研究擬以擠壓技術開發PHBV/ PVA為基底之生物可分解塑膠粒，透過熔融混煉的方式，將生物可分解高分子聚羥基丁酯戊酯(Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV)、特定水解度之聚乙烯醇(Poly(vinyl alcohol), PVA)與可再生資源澱粉進行混煉，獲得生物複合塑膠粒。研究主題分為三部分：(1)以反應曲面法尋找PHBV/ PVA/ 玉米澱粉混煉塑膠粒之最適配方；(2)以PHBV/ PVA/ 樹薯澱粉開發生物可分解塑膠粒，並找尋最適操作條件與探討其理化特性；(3)PHBV/ PVA為基底之生物複合塑膠粒之商品化測定。本論文之各部分內容敘述如下：
Formulation optimization of poly(hydroxybutyrate-co-hydroxyvalerate)/ poly(vinyl alcohol) blended with corn starch blends via response surface methodology
Section 1：以擠壓機混煉PHBV/ PVA/ 玉米澱粉，添加塑化劑(甘油和檸檬酸三乙酯)進行改質，利用反應曲面法三變數三層級之實驗設計，共計15組實驗組別。每一處理組總重為1 kg，其中主副原料佔75%，塑化劑占25%。將物料經擠壓機混煉後，將處理組進行機械性質、吸水率、樣本表面結構分析等測定項目，結果透過統計迴歸分析配合等高線圖，可得到在最高0.71的期望值(desirability)下之最適操作條件之範圍與其對應之反應性狀。
Section 2：由第一階段找出原料最適配方後，由反應曲面法瞭解不同塑化劑量對PHBV/ PVA/ 玉米澱粉混煉後之反應性狀之影響及尋找塑化劑之最適配方。以不同塑化劑作為操作參數，透過反應曲面法三變數三層級之實驗設計，設定操作參數：甘油添加量(80 g、92.5 g、105 g)、檸檬酸三乙酯(triethyl citrate, TEC)添加量(35 g、55 g、75 g)、癸二酸二辛酯(dioctyl sebacate, DOS)添加量(15 g、25 g、35 g)。將物料經擠壓機混煉後進行測定。根據各項測定結果可知，塑化劑增加塑膠粒之拉伸性質但減低荷重，由統計結果可知，甘油及TEC對最大拉伸荷重有負向的二次效果(square effect)，而對吸水率有正向的二次效果，DOS則對於最大拉伸位移有較大的正向線性效果(linear effect)。由期望函數的計算可得到一期望值為0.79下的最適合的塑化劑添加量。藉由運用反應曲面法，不僅瞭解操作參數對各反應性狀之影響模式，更可找出塑化劑之最適添加配方。
Formulation optimization and characterization of poly(hydroxybutyrate-co-hydroxyvalerate)/ poly(vinyl alcohol) blended with tapioca Starch
Part II是以Part I中所得到PHBV/ PVA之最適比例，搭配低成本的樹薯澱粉，輔以偶合劑馬來酸酐增強材料相容性，透過一次性擠壓技術將其混煉加工，開發生物可分解塑膠粒，並進行其機械性質分析、熱分析等分析項目，探討反應性狀與操作參數間之關係。期望藉由此生物可分解塑膠粒之最適操作條件範圍，可作為未來產業商品化之依據。此階段採用反應曲面法之三變數三層級之實驗設計，設定樹薯澱粉比例、螺軸轉速及不同添加比例之馬來酸酐比例為操作參數。每一處理組總重為1 kg，其中主副原料佔75%，塑化劑占25%，共計15組實驗組別。將物料經擠壓機混煉後，測定並探討其機械性質、物理性質、熱特性、樣本表面結構性質等項目。根據各項測定結果可知，樹薯澱粉添加比例及馬來酸酐比例對於最大拉伸荷重、最大拉伸位移及吸水率之線性項有極顯著的影響，而且各迴歸模式具有超過90%的判定係數(coefficient of determination)，且為無顯著之缺適性(lack-of-fit)，表示可利用各模式進行找尋最適操作條件。得到最適操作條件後，將實際值與預估值進行t檢定，結果無顯著差異。
Further test prior to commercialization of the poly(hydroxylbutyrate-co-hydroxyvalerate)/ poly(vinyl alcohol)/ tapioca starch pellets
論文Part III則將先前得到的最適配方塑膠粒，依照EN13432標準中有關可堆肥包裝材料所需性質來進行測試，依照ISO 14855標準進行生物分解能力之測試、依照ISO 20200標準進行崩解度之測定、依照EN 71-3標準進行溶出物之重金屬含量測定及依照CNS 15138進行有害塑化劑含量測定。由實驗結果可得，塑膠粒之生物分解率為83.3%。並得塑膠粒之崩解度達到合乎檢測範圍(90%以上之殘餘物可通過孔徑2 mm之標準篩網)之天數。塑膠粒之可溶性重金屬含量及有害塑化劑含量之測定亦合乎規範。期望藉由此等生物可分解塑膠粒之相關檢測，作為未來商品化之參考依據。|
The dissertation elucidates the development of biodegradable pellets base on poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)/ particular hydrolyzed poly(vinyl alcohol) (PVA) by extrusion techniques and the pre-commercial studies. The topic include: (i) formulation optimization of PHBV/ PVA blended with corn starch blends via response surface methodology; (ii) optimization and characterization of PHBV/ PVA blended with tapioca starch; (iii) Further test prior to commercialization of the PHBV/ PVA/ tapioca starch pellets. The contents of each part are listed below: Part I: Formulation optimization of poly(hydroxybutyrate-co-hydroxy-valerate)/ poly(vinyl alcohol) blended with corn starch blends via response surface methodology Section 1: The extrusion technology was used to produce the biodegradable plastic pellets composed by biopolymers (PHBV, PVA and corn starch) blended with the fixed content of plasticizers glycerol and the triethyl citrate. Response surface methodology (RSM) which adopted a three-variable and three-level experimental design was chosen for finding out the relationship between the responses (maximum loading, maximum displacement, water absorption) and the process variables, and used to analyze the composition of PHBV/ PVA/ corn starch. The total weight of one treatment was 1 kg including the major and auxiliary formulations 75% and the plasticizers 25%, respectively. The optimized ranges of operating conditions were determined by optimization process in RSM. Superimposing the individual contour plots affected by process variables resulted were obtained at a desirability value of 0.71. Section 2: This study investigated the effects of plasticizers (glycerol, triethyl citrate (TEC) and dioctyl sebacate (DOS)) on the physical properties of bioplastic pellets based on PHBV/ PVA/ corn starch using response surface methodology (RSM). Experiments were designed according to a Box-Behnken design (BBD) to quantify the relationship between the variables and responses and to present mathematical models as a function of plasticizers for the prediction of maximum loading, maximum displacement, and water absorption of the blends. Three levels were chosen for the considered variables as follows: glycerol (80, 92.5, 105 g), TEC (35, 55, 75 g), and DOS (15, 25, 35 g). These plasticizers increased the flexibility, but decreased the maximum loading. Glycerol and TEC have a negative square effect on maximum loading and an opposite effect on water absorption. DOS content has a greater positive linear effect on maximum displacement. Applying the method of Derringer's desirability function, the modelled optimization conditions for the desired performance were obtained at a desirability value of 0.79. Finally, the results were consistent with the BBD prediction for optimum plasticizer conditions thus obtained, indicating the proposed model is highly suitable for industrial usage. Part II: Formulation optimization and characterization of poly(hydroxybutyrate-co-hydroxyvalerate)/ poly(vinyl alcohol) blended with tapioca starch In this part, tapioca starch was considered as a replacement for the corn starch for reducing production costs. Also maleic anhydride was selected as a compatibilizer for improvement of adhesion between the matrixes. PHBV, PVA and tapioca starch are environment-friendly materials. The present study used these materials to produce biodegradable plastic pellets by melt extrusion. The tapioca starch content of composite formulations, the maleic anhydride content and the screw speed of extruder were chosen as variables for the extrusion process. A Box-Behnken response surface design was used to establish mathematical models to predict the relationship between the operating variables and the objective attributes (maximum loading, maximum displacement, and water absorption) of the blends. Blend morphology and thermal properties were also assessed. The regression coefficients revealed that the extrusion parameters most significantly affecting extrudate responses were tapioca starch content and maleic anhydride content, both showing significant (p < 0.01) linear effects. The results of the analysis of variance found the models are in good agreement with experimental results as informed by high coefficient of determination (R2 > 0.9), with no significant lack-of-fit, thus indicating suitability of the used model and the response surface methodology for system optimization. Part III: Further test prior to commercialization of the poly(hydroxylbutyrate-co-hydroxyvalerate)/ poly(vinyl alcohol)/ tapioca starch pellets In accordance with the required analyses of compostable packaging materials in EN 13432, the objective in Part III was to investigate the biodegradability and disintegrability of the extruded pellets. Biodegradability of the sample was measured in controlled compost according to ISO 14855. The biodegradability of extruded pellets reached 83.3%. An evaluation of the disintegration of pellets was assessed according to ISO 20200. The end of the disintegration of the PHBV/ PVA/ tapioca starch blend was obtained, when it was considered to be totally disintegrated. As it can be seen, 90% of the test materials were passed through a 2 mm sieve met standard requirements. Validity of sample preparation method for biodegradable pellets was confirmed. Phthalates and soluble heavy metals contents of PHBV/ PVA/ tapioca starch blend were not detected which analyzed according to norms CNS 15138 and EN 71-3, respectively.
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