蚕丝纤维增强聚乳酸体系中柱晶的形成及其结构分析

发布时间：2018-08-31 17:13

【摘要】：聚乳酸(PLA)具有较好的机械性能、生物相容性以及可降解性,应用于生物医疗和包装领域。由于PLA的结晶速率慢,传统工艺条件下得到的制品多为非晶结构,导致其呈脆性大,耐热性不佳,因此极大的限制了PLA的应用。对于纤维增强的聚合物基复合材料,纤维改性是改善PLA结晶性能,提高制品结晶度的有效方法。本课题选天然蚕丝(SF)作为增强材料,利用碳酸钠溶液对蚕茧脱胶,得到蚕丝纤维(丝素纤维),利用溶液法制备PLA薄膜,将单根蚕丝纤维放置于两PLA薄膜之间,制成“三明治”结构的试样,研究了等温温度和牵引速率对SF/PLA界面结晶形貌的影响。首先,利用偏光显微镜(POM)研究了等温过程中柱晶(或球晶)的结晶行为和晶体形貌,分析了等温温度、SF牵引速率以及牵引时间对晶体形貌的影响;其次,利用显微红外光谱(FTIR)对柱晶的晶体类型、结晶度及取向度进行了表征;最后,考察了小含量(5 wt%)的聚氧化乙烯(PEO)对PLA结晶行为的影响,主要内容简述如下:(1)等温温度在100-130℃之间,牵引速率为0时,SF表面无法诱导PLA结晶。温度较低时(120℃),由于过冷度较大,PLA基体的成核很快,较小的球晶迅速充满POM观测区域,很难观察SF对PLA结晶行为的影响,本实验表明120-130℃是研究SF诱导PLA结晶行为的理想温度区间。(2)利用POM研究了牵引速率对SF/PLA界面结晶行为的影响,发现牵引速率不同,PLA在SF表面上的结晶形貌不同。牵引速率较小时,SF表面上形成“串形球晶”结构,牵引速率增大,“串形球晶”转变为柱晶结构,牵引速率过大时,蚕丝纤维发生断裂。无论是形成“串形球晶”还是柱晶,其结晶诱导时间都随牵引速率的提高而缩短,成核速率、最终晶核密度则随牵引速率的提高而增大。等温温度为120℃时,生成“串形球晶”的临界牵引速率为5μm/s,形成柱晶的临界牵引速率为40μm/s,蚕丝纤维在牵引过程中发生断裂的牵引速率为150μm/s,而130℃条件下的三个临界速率分别为10、50和250μm/s。相同牵引速率下,120℃等温时,PLA的结晶诱导时间更短,成核速率更大,最终晶核密度更高。(3)以牵引时间为变量,固定牵引速率为40μm/s,研究牵引时间对界面结晶形貌的影响,发现牵引时间与牵引速率具有类似的效果,延长牵引时间,PLA在SF表面的结晶形貌由“串形球晶”变成柱晶结构,即成核密度随牵引时间的延长而增加,与130℃相比,120℃条件下,PLA在SF表面的成核密度更高,成核速率更快。(4)利用FTIR分析牵引速率对PLA柱晶的晶型、结晶度和取向度的影响,发现牵引速率不能改变PLA的晶体类型,柱晶均为α晶体结构。120℃条件下,随着牵引速率提高,柱晶的结晶度提高,取向度增加。130℃条件下的实验结果与120℃基本一致,不同之处在于,牵引速率超过临界值时(100μm/s),柱晶的结晶度和取向度分别趋于固定值。(5)探究小含量的聚氧化乙烯(PEO)对SF/PLA复合体系结晶行为的影响,发现PEO加入后,开始在SF表面生成“串形球晶”和柱晶的临界牵引速率均提高,此外,PEO还明显提高了PLA的晶体生长速率。
[Abstract]:Polylactic acid (PLA) has good mechanical properties, biocompatibility and biodegradability, and is widely used in biomedical and packaging fields. Due to the slow crystallization rate of PLA, the products obtained under traditional process conditions are mostly amorphous structure, resulting in its brittleness and poor heat resistance, which greatly limits the application of PLA. Fiber modification is an effective method to improve the crystallinity and crystallinity of PLA. In this paper, natural silk (SF) was selected as reinforcing material, cocoon was degummed with sodium carbonate solution, and silk fiber (fibroin fiber) was obtained. PLA film was prepared by solution method, and single silk fiber was placed between two PLA films to make "SF" as reinforcing material. The effects of isothermal temperature and traction rate on the crystal morphology of SF/PLA interface were studied. First, the crystallization behavior and morphology of columnar (or spherulite) crystals were studied by polarizing microscope (POM), and the effects of isothermal temperature, SF traction rate and traction time on the crystal morphology were analyzed. Microscopic infrared spectroscopy (FTIR) was used to characterize the crystal type, crystallinity and orientation of the columnar crystals. Finally, the effect of polyethylene oxide (PEO) with small content (5 wt%) on the crystallization behavior of PLA was investigated. The main contents were summarized as follows: (1) SF surface could not induce the crystallization of PLA when the isothermal temperature was between 100 -130, and the traction rate was 0. It is difficult to observe the effect of SF on the crystallization behavior of PLA because of the large degree of undercooling and the rapid nucleation of PLA matrix and the small spherulite filling the POM observation region. The experiment shows that 120-130 C is the ideal temperature range for studying the crystallization behavior of PLA induced by SF. (2) The influence of the traction rate on the crystallization behavior of SF/PLA interface was studied by POM. When the traction rate is low, the "string spherulite" structure is formed on the SF surface, and the "string spherulite" is transformed into columnar structure. When the traction rate is too high, the silk fibers break down. Whether the "string spherulite" or columnar crystal is formed, the induction time of crystallization varies with the traction time. The critical traction rate for the formation of string spherulites is 5 micron/s, the critical traction rate for the formation of columnar crystals is 40 micron/s, and the traction rate for the breakage of silk fibers during traction is 150 micron/s and 130 micron/s respectively. At the same traction rate, the induction time of PLA crystallization is shorter, the nucleation rate is higher, and the final nucleation density is higher at 120 C. 3. The influence of traction time on the interfacial crystallization morphology is studied by taking the traction time as variable and the fixed traction rate as 40_ micron / s. The nucleation density of PLA on SF surface increased with the extension of traction time. Compared with 130 C, the nucleation density of PLA on SF surface was higher and the nucleation rate was faster at 120 C. (4) FTIR was used to analyze the effect of traction rate on PLA columnar crystal. It was found that the traction rate could not change the crystal type of PLA, and the columnar crystals were all alpha crystals. At 120 C, the crystallinity and orientation of columnar crystals increased with the increase of traction rate. The experimental results at 130 C were basically the same as those at 120 C. The difference was that the traction rate exceeded the critical value. The crystallinity and orientation of the columnar crystals tend to be fixed at 100 micron/s. (5) The effect of small content of polyethylene oxide (PEO) on the crystallization behavior of SF/PLA composite system was investigated. It was found that the critical traction rate of string spherulites and columnar crystals on SF surface increased with the addition of PEO. Rate.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O633.14;O631.13

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