生物可分解性高分子聚乳酸與澱粉之結晶行為與物性研究

The Investigation of Biodegradable Polylactic Acid and Starch in Crystallization Behavior and Characterizations

劉佳怡(Chia-I Liu)

指導教授 ： 黃繼遠

大同大學/工程學院/材料工程學系所/博士(2009年)

摘要

本研究中探討聚乳酸(PLA)或聚乙烯醇(PVA)與馬來酸酐接枝物(MA-g-PLA)之掺合物，加工混煉後之熱性質變化。FT-IR與μ-FTIR也被應用於證實，馬林酸酐確實接枝於聚乳酸高分子中，利用滴定法獲知MA-g-PLA接枝量約為1.625×10-4 mol/g。由DSC觀察掺合物之熱性質變化得知，PLA經加熱後趨於形成透明非結晶結構，加入PVA更形成一非穩定性系統(meta-stable system)，然而添加2.5g相容劑後，掺合物出現明顯再結晶現象，結晶度約為33%，隨著相容劑添加量至12.5g，掺合物之結晶度降至22%，並出現兩個熔融峰於147℃與153℃，經確認後分別為條狀之β-phase與螺旋狀之α-phase，隨著相容劑添加量增加，掺合物之β-phase結晶度也趨於增加。由XRD量測退火處理之掺合物試片，掺合物於加熱溫度80℃產生一微弱結晶峰，90℃至130℃形成一強烈結晶峰，可證實DSC中再結晶峰之溫度起點。
由早期之研究得知，添加澱粉(starch)與甘油(GA)之掺合物，具有低拉伸強度、低伸長量與低流動能力之特性，因此本實驗藉由改質澱粉，做為澱粉掺合物之塑化劑改善上述之缺點。分別將澱粉進行水解與酸解(0.1M、0.3M、0.5M之檸檬酸溶液，簡稱CA)處理，再加入30wt%、50wt%、70wt%添加量於掺合物中觀察物性之變化。添加50wt%水解澱粉時，掺合物之拉伸強度約為3.75MPa伸長量可提升至225%，明顯改善添加澱粉與甘油之掺合物，機械性質不佳之特性。由MFI(Melt Flow Index)測試得知添加70wt% 0.3M CA-starch，掺合物MFI值可達300g/10min，流動性獲得明顯改善。由XRD量測可觀察到0.1M CA-starch結晶度大幅度降低，隨著酸濃度增加改質澱粉之結晶度再次提升。進一步，46KHz之超音波被應於改質澱粉製程中，觀察掺合物之物性變化。於水解或酸解澱粉中施予超音波處理，有助於澱粉分子鏈間之氫鍵斷裂使分子鏈更容易移動，進一步提升掺合物之流動能力。由MFI測試得知隨著超音波處理時間由0min 增至10min，掺合物之MFI值由0.5g/10min提升至5.5g/10min。使用發酵堆肥土做為生物分解性測試之土壤，由SEM觀察分解試片之表面變化可獲知菌類成長之過程。
此外，本實驗在天然澱粉/水解澱粉掺合物中，另加入經鈦系偶合劑處理之碳酸鈣，來增加掺合物疏水性與熱熔融流動性。由SEM觀察得知添加水解澱粉之掺合物脆斷面有大量孔洞出現，然而添加經鈦系偶合劑處理之碳酸鈣，隨著添加量增加至25wt%碳酸鈣仍可均勻性分布於掺合物中。在DSC測試中添加5wt%鈦系偶合劑處理之碳酸鈣導致掺合物之焓由213J/g降至109J/g，因為碳酸鈣表面之偶合劑過度塑化掺合物之分子鏈所致。在MFI測試中，添加25wt%偶合劑處理碳酸鈣的掺合物表現出良好的熱熔融流動性，MFI值可高達70g/10min。當掺合物添加經偶合劑處理之碳酸鈣時，掺合物表現出良好的疏水性，碳酸鈣含量為15wt%時，掺合物之接觸角由60°增加至95°。在生物分解測試中，掺合物裡添加偶合劑處理之碳酸鈣並不影響其生物分解性，分解率仍可維持至50~75%。

關鍵字

疏水性 ； 結晶行為 ； 生物可分解 ； 聚乳酸 ； 澱粉

並列摘要

In this research, poly(lactic acid)/poly(vinyl alcohol)/maleic anhydride-g-poly(lactic acid)(denoted as PLA/PVA/MA-g-PLA) blends were prepared by compounding to study the thermal properties. The FTIR and μ-FTIR were employed to demonstrate the grafting of MA on PLA, and the grafting degree of MA-g-PLA was 1.625×10-4 mol/g measured by a titration method. A thermal analyzer, DSC, showed that the PLA/PVA blends should be a meta-stable system. However, the affinity from the compatibilizer MA-g-PLA could make the PLA/MA-g-PLA/PVA blends become a stable system. Besides, the crystallinity of PLA blends appeared a significantly increase from amorphous state to crystallinization of 33% as addition of compatibilizer was 2.5g. There were two melt peaks at 147℃and 153℃ to show the sheet shape β-phase and helix shape α-phase. The reason was confirmed that PLA resulted in more β-phase crystallization by adding the compatibilizer. A weak crystalline peak was appeared in the blend after a annealing treatment at 80℃. Then, some strong crystalline peaks were observed when the annealing temperatures were from 90℃ to 130℃. The XRD results demonstrated the onset temperature of recrystallinization of PLA blends.
In previous studies, starch/glycerol(GA) blends presented those characters such as low tensile strength、low elongation and poor melt flow ability. Therefore, aim of this study was to improve above disadvantages by modifying starches. A variety of modified starches, which was treated by hydrolysis and acid hydrolysis(0.1M、0.3M、0.5M citric acid solution). Tensile strength of blend with 50wt% hydrolysis starch was 3.75MPa, but the elongation could reach to 225%. The mechanical properties of starch/GA blends were obviously improved by adding modified starch. The MFI of blends increased to 300g/10min when the addition of acid hydrolysis starch (0.3M CA-starch) was 70wt%. The melt flow ability of blends had a significant improvement. The crystallinty of 0.1M CA-starch presented a decreased and then crystallinity of modified starch increased as acid solution was 0.3M and 0.5M. The crystalline behaviors of modified starches were also studied by ultrasonic treatment at 46 KHz of frequency. The ultrasonic treatment could prove the energy to break hydrogen bonds between molecular chains, and the melt flow ability of blends was obviously improved. The MFI of blends increased from 0.5g/10min to 5.5g/10min when the time of ultrasonic treatment increased from 0min to 10min. The SEM micrographs of blends also showed the growth process of fungi on the surface of specimens during the biodegradation.
Calcium carbohydrate which was treated by titanium coupling agent ( denoted as Ti-CaCO3 ) was also added to improve hydrophilicity and melting flow behavior in the starch blends. SEM micrographs showed that there were a lot of holes in the native starch/ hydrolysis starch blends. Moreover, Ti-CaCO3 dispersed uniformly in the native starch/ hydrolysis starch blends when the addition of Ti-CaCO3 reached to 25wt%. The enthalpy of blend with 5wt% Ti-CaCO3 decreased from 213J/g to 109J/g in the DSC measurement. The reason was considered that coupling agent on the surface of CaCO3 plasticized excessively molecular chains. The blend also presents a high MFI (melt flow index) to 70g/10min when the addition of Ti-CaCO3 reached to 25wt%. Furthermore, the blends with Ti-CaCO3 presented an excellent hydrophobility. Water contact angle of blend increased from 60° to 95° as the addition of Ti-CaCO3 was 15wt%. Beside, biodegradation of the blends were not affected by adding Ti-CaCO3. Weight loss of native starch/hydrolysis starch blend with Ti-CaCO3 was between 50% and 75% after the biodegradation for one week.

並列關鍵字

biodegradation ； polylactic acid ； tapioca starch ； crystallization ； hydrophobility

參考文獻

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