新穎生物高分子共聚酯與石墨烯複合材料製備與應用之研究

The study of preparation and application of novel biopolymer copolyester and graphene composites

楊健和(Chien-Ho Yang)

指導教授 ： 李育德 ； 蔡宏斌

國立清華大學/工學院/化學工程學系/博士(2012年)

摘要

摘要
以石油為基礎原料的塑膠材料，廣泛應用在生活的各個層面，大幅提升了日常生活的舒適性，現今全球各類塑膠的年需求量已經超過2 億公噸，但每年仍然持續成長，但此類材料大部份具有不易分解或對生物具有毒性之缺點，當大量使用時，預期必將造成嚴重的環保和社會問題，因此可利用具生物分解性(biodegradable)或生物相容性(biocompatiable)的生物高分子取代現在使用的泛用塑膠，以避免或減輕此類問題。
本研究可分為兩部份，第一部份乃是利用共聚合的方式，調控生物分解性之左旋聚乳酸(PLLA)之熱性質、生物分解速率等性質，以增加PLLA在工業或民生用品上應用之潛力。第二次部份則是利用少量之石墨烯分別導入生物相容性聚乙烯醇(PVA)與PLLA，改善高分子之熱穩定性、結晶性質，並賦予優良之導電性，以拓展此類生物高分子於光電應用之可能性。
在PLLA共聚高分子的研究中，主要是利用陽離子開環製備PLLA-PTMEG-PLLA(TMLA)與PLLA-PC-PLLA(PCLA)之三嵌段共聚高分子，以及利用轉酯化反應製備PET-r-PLLA(ETLA)與PBT-r-PLLA(BTLA)亂排共聚酯。在PCLA共聚高分子的部份，脂肪族之PC與PLLA互為相溶，其Tg亦隨著PLLA含量上升而提高，且PC的含量提升可有效的減少PLLA之結晶度，可利用脂肪族PC導入，或調控PLLA之透明度。由生物分解測試的結果，可確定其分解反應是由非結晶區(amorphorous region)先開始，且隨著測試時間增加分解量亦增加，足見PLLA於共聚物中仍保有生物分解性。而在TMLA共聚高分子的部份，由於PTMEG與PLLA互為不溶，使PLLA之熱性質可得到最大程度的保留。且經由酵素分解測試，發現改變PTMEG的含量，可有效的調控PLLA分解的速率，在應用上，可針對不同壽命(life time)須求的產品進行設計。此外，在PET、PBT分別與PLLA共聚合而得之亂排共聚酯方面，以一次進料的方式以聚縮合反應器合成，可成功的生產出新穎之PLLA亂排共聚酯，相較於多次進料法，此法在生產效率上較為優異。且由酵素分解測試結果，可發現PET或PBT的導入，可有效的延遲PLLA之分解時間，並應用於使用壽命較長的產品中。
在生物高分子與石墨之烯複合材料方面，利用減小氧化石墨烯(GO)尺寸的方式，可製備GO含量高達14wt%且均勻分散之GO/PVA複合材料，並提升PVA熱穩定性(Td-s提升約100oC)，成功的利用GO的原位還原法，製出高rGO含量且分散均勻之rGO/PVA複合材料，並表現出優異的導電性(rGO 14wt%時，5.92 S m-1)。
在熱還原石墨烯(TRG)與PLLA複合材料(GLLA)的部份，利用熔融陽離子開環聚合法，成功的製備GLLA複合材料，証明TRG上殘於之-OH可直接作為PLLA聚合反應之起始官能基，亦可推論此類-OH基或可進行其它反應。此外TRG可作為成核劑，提升PLLA初期的結晶速率，但隨著TRG含量增加，亦可利用其間所產生的空間阻礙，控制PLLA最大結晶度的範圍。由型態學觀察結果，可確定由共價鍵結法結合之複合材料，具有優異的介面作用力，避免材料缺陷產生，亦是此緣故，TRG微量的導入，即可賦予PLLA良好的導電性質(TRG於2wt%時，1.63×10-2 S m-1)。
綜言之，利用共聚合的方式控制生物高分子之Tg、結晶度、分解速率以及延遲其分解時間，以及石墨烯不同方法導入製成導電複合材料，期望在未來上，可將生物高分子之實際應用率大幅的提高，以避免不環保泛用塑膠的使用。

關鍵字

聚左旋乳酸 ； 石墨烯 ； 開環反應 ； 原位共聚合

並列摘要

Abstract
In this study, a series PLLA triblock copolymers and random copolymers were synthesized for adjusting various properties of PLLA. Expect to increase the application potential of biodegradable PLLA by introducing these polymers, including PTMEG, aliphatic PC, PET and PBT, respectively. For electrical application purpose, we also introduced graphene oxide(GO) and graphene(rGO and TRG) into biopolymers, PVA and PLLA, respectively.
In the part of ABA triblock copolymers, a series of ABA triblock copolymers of PLLA and aliphatic polycarbonate (PCLA) have been synthesized and thoroughly characterized. PLLA and aliphatic PC are miscible and its Tg is increased with increasing PLLA content. The crystallinity of PLLA is decreased with increasing PC content. These tendency might be used for adjusting the transparency of PLLA. According to the results of biodegradability test, we found that the PLLA in PCLA triblock copolymers is still biodegradable and the degradation is starting from the amorphous region.
A series of ABA triblock copolymers of PLLA and PTMEG(TMLA) have been also synthesized and thoroughly characterized. In enzymatic degradation, through the manipulation of PTMEG content in the triblock copolymer, the hydrolysis rate of PLLA segment by enzyme can be well controlled. The enzymatic degradation of PLLA segment decreases with increasing PTMEG content in the copolymer, while the weight loss percentage of the PLLA segment increases exponentially with time, indicating that the enzymatic degradation of PLLA segment is a diffusion-controlled process. Besides, the random copolymer, PET/PLLA and PBT/PLLA also had been synthesized and thoroughly characterized. The series of random copolymers display a long-term biodegradation, indicating that the introduction of PBT or PET with random form could retard the biodegradation of PLLA.
In the part of graphene/biopolymer composites, GO/PVA composites were prepared and thoroughly characterized. Through a convenient effective method, uniform dispersed reduced graphene oxide(rGO)/PVA composites could be obtained by swelling the PVA matrix with a reducant solution. The electrical conductivity of the composite increases with increasing rGO content, while a sharp increase happens as the rGO content beyond 10wt%. Such an increase was evidenced by the formation of rGO network so as to diminish the electrical resistance by the interconnection structure of rGO. In our studies, the conductivity of rGO/PVA film increases from 6.04×10-3 S/m to 5.92 S/m as the rGO content increases from 4wt% to 14wt%.
A series of poly(L-lactide) (PLLA)/thermally reduced graphene oxide (TRG) composites (GLLA) were prepared via the in situ ring-opening polymerization of lactide, with TRG as the initiator; after their preparation, the composites were characterized. By using a more effective method of synthesis, the thermal stability, crystallization rate, and electrical conductivity of PLLA were increased. The starting temperature for the thermal decomposition of PLLA was increased from 173oC to 211oC via the introduction of 2.00wt% TRG sheets. At a TRG content of 2.00wt%, the chemical interaction between the PLLA and the TRG sheets was strong enough to increase the nucleation rate and the overall crystallization rate of the PLLA. The electrical conductivity of the GLLA composites increased with increasing TRG content. Typical insulating-conductive percolation behavior was observed for TRG contents between 1.00 and 1.50wt%, and the electrical conductivity of the PLLA was improved by 12 orders of magnitude in the GLLA composites, from 7.14×10-14 S/m for neat PLLA to 1.63×10-2 S/m for GLLA with 2.00wt% of TRG sheets. These results demonstrate a straightforward means of preparing GLLA composites that perform satisfactorily in terms of their electrical conductivity and their thermal stability.
In conclusion, the Tg, crystallinity and biodegradation rate of PLLA could be adjusted or controlled by copolymerized with other polymers. Besides, introduction of GO and TRG could enhance the thermal stability of biopolymer PVA and PLLA respectively and endowed the biopolymers(PLLA and PVA) with an outstanding electrical conductivity. To sum up, these improvement raised the applied potentials of PLLA, successfully.

並列關鍵字

PLLA ； graphene

參考文獻

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