Influence of High Pressure on Single-Crystal Growth of Poly(L-Lactic Acid) in the Solution
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摘要: 采用高压技术实现了500 MPa下聚左旋乳酸(PLLA)在稀薄二甲苯溶液中的单晶生长，采用透射电子显微镜、拉曼光谱和红外光谱对样品的结晶形态和结构进行了表征，考察了高压对聚左旋乳酸单晶生长行为的影响。结果表明，在相同的结晶温度和时间下，高压结晶PLLA的单晶仍为α-型晶体，但单晶尺寸明显大于常压样品；高压环境下PLLA分子链在晶核两端的生长扩散速率不同，容易形成非对称的菱晶形态；高压影响PLLA晶体中分子链的构象分布；在单晶生长期，高压诱导有利于PLLA晶体成核，但不利于单晶生长。
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关键词:
- 聚左旋乳酸(PLLA) /
- 等温结晶 /
- 高压 /
- 单晶
Abstract: Lamellar single crystals of poly (L-lactic acid) (PLLA) were prepared from its dilute xylene solutions under 500 MPa by an isothermal crystallization method.Their morphology and structural features were characterized by transmission electron microscopy, raman and infrared spectra.The results show that the single crystals of PLLA grown under high pressure are only α-type crystal structure, and their average size is larger than those obtained under atmospheric conditions.Under high pressure, crystal nucleus on different sides have different growth rates, leading to the formation of asymmetric rhombic lozenge.It is found that high pressure has induced conformational distribution change of the PLLA single crystal.Furthermore, during the PLLA crystal growth period, high pressure induction is favorable for promoting the nucleus number and depressing the grown of PLLA crystal.-
Key words:
- poly (L-lactic acid) (PLLA) /
- isothermal crystallization /
- high pressure /
- single crystal
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图 2 不同结晶条件下制备的PLLA单晶的红外光谱图(PLLA-0为初始原料)
Figure 2. FT-IR spectra of PLLA single crystals grown under different pressures in the solution (Here PLLA-0 is the initial material)
图 3 不同条件下制备的PLLA单晶的拉曼光谱图
Figure 3. Raman spectra of PLLA single crystals grown under different pressures in the solution
图 4 不同条件下制备的PLLA单晶的透射电子显微镜照片
(a) PLLA-1 (b) PLLA-2 (c) PLLA-3
Figure 4. TEM images of PLLA single crystals grown under different conditions in the solution
表 1 样品拉曼光谱中拉曼峰1 044、1 090和1 128 cm-1相对强度
Table 1. The relative intensity of the fingerprint peak of samples at 1 044, 1 090 and 1 128 cm-1
Relative intensity(a) PLLA-0 PLLA-1 PLLA-2 PLLA-3 I′1 044 0.70 0.79 0.75 0.80 I′1 090 0.54 0.59 0.83 0.58 I′1 128 1.00 1.00 1.00 1.00 Note:(a) I′1 044=I1 044/I1 128; I′1 090=I1 090/I1 128; I′1 128=I1 128/I1 128. 
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