Crystallization and degradation behavior of poly(lactic acid)/poly(ethylene glycol) blends

doi:10.11949/0438-1157.20200323

Abstract

Abstract:

Aiming at the problem of poor hydrophilicity and long degradation period of polylactic acid (PLLA), it is modified by blending with hydrophilic polymer polyethylene glycol (PEG). A series of PLLA/PEG blends with different blend compositions were prepared by melt blending in torque rheometer. The crystallization and melting behavior, hydrophilicity and degradation properties of PLLA/PEG blends were systematically studied. Results shows that the addition of PEG enhances both the crystallization ability of PLLA and its crystallization temperature during cooling. In isothermal crystallization process, the crystallization rate of PLLA in blends is much faster than that of pure PLLA. Hydrophilicity and degradation rate of the material can be tuned by varying the blend composition. The surface contact angle of PLLA/PEG blends decreases with the increase of PEG content. Both PLLA and PLLA/PEG blends can be degraded in aqueous solution; the degradation ability is significantly improved with PEG presents. The degradation rate of PLLA/PEG blends can be accelerated by increasing of PEG content and increasing of acid or alkali solutions concentration.

Key words: polylactic acid, poly(ethylene glycol), crystallization, blend, degradation

摘要：

针对聚乳酸（PLLA）亲水性差、降解周期长的问题，利用与亲水性高分子聚乙二醇（PEG）共混的方法对其进行改性。采用转矩流变仪制备了不同组成的PLLA/PEG共混物颗粒，系统研究了PLLA/PEG共混物的结晶和熔融、亲水性和在酸碱介质中的降解行为。结果表明，PEG的加入增强了共混物中PLLA的结晶能力，提高了PLLA在降温过程中的熔融结晶温度。PLLA/PEG共混物在等温结晶中表现出比纯PLLA更快的结晶速度。通过改变PLLA/PEG共混物的组成，可调控材料的表面亲水性和降解速率。随着PEG含量的增多，PLLA/PEG共混物的表面接触角降低。PLLA与PLLA/PEG共混物均可在水溶液中降解，共混物的降解速率高于纯PLLA，随着PEG含量的升高和降解液中酸碱浓度的提高，PLLA/PEG共混物的降解速率加快。

关键词: 聚乳酸, 聚乙二醇, 结晶, 共混, 降解

CLC Number:

TQ 323.4

ZHANG Kuangsheng, TANG Meirong, XUE Xiaojia, LI Kai, SHAO Yan, ZHOU Jian, YUE Chongchong, LI Zhuangzhuang, PAN Pengju. Crystallization and degradation behavior of poly(lactic acid)/poly(ethylene glycol) blends[J]. CIESC Journal, 2021, 72(2): 1181-1190.

张矿生, 唐梅荣, 薛小佳, 李楷, 邵炎, 周健, 岳冲冲, 李壮壮, 潘鹏举. 聚乳酸/聚乙二醇共混物的结晶与降解行为[J]. 化工学报, 2021, 72(2): 1181-1190.

Figures/Tables 10

Fig.1 Appearance (left) and SEM image (right) of PLLA/PEG blended particulates

Fig.2 Tensile properties of PLLA/PEG blends

Fig.3 DSC curves of PLLA, PEG and PLLA/PEG blends

Table 1 Thermal parameters of PLLA, PEG and PLLA/PEG blends

Sample	T_c,PEG /℃	T_c,PLLA/℃	ΔH_c,PLLA/(J/g)	T_m,PEG/℃	T_m,PLLA/℃	ΔH_m,PLLA/(J/g)	X_c,PLLA/%
PLLA	—	—	—	—	174.6	29.7	31.8
PLLA₉₀PEG₁₀	—	93.6	43.8	45.1	175.2	44.1	47.4
PLLA₈₀PEG₂₀	—	95.6	41.4	51.7	173.7	55.4	59.5
PLLA₇₀PEG₃₀	24.5	95.7	51.3	57.2	173.6	57.6	61.8
PLLA₆₀PEG₄₀	34.6	109.6	51.8	59.2	172.8	61.2	65.6
PLLA₅₀PEG₅₀	33.5	107.1	53.8	59.3	171.6	62.6	67.2
PEG	35.8	—	—	63.9	—	—	—

Fig.4 Results of PLLA and PLLA/PEG blends during isothermal crystallization at 120℃

Table 2 Kinetic data of PLLA and PLLA/PEG blends during isothermal crystallization at 120℃

Sample	t_1/2/min	k/min^-ⁿ	n
PLLA	8.5	0.01	2.08
PLLA₉₀PEG₁₀	2.6	0.11	1.90
PLLA₈₀PEG₂₀	2.2	0.13	2.15
PLLA₇₀PEG₃₀	2.0	0.12	2.51
PLLA₆₀PEG₄₀	1.7	0.18	2.63
PLLA₅₀PEG₅₀	0.8	1.05	2.01

Fig.5 Spherulitic morphology of PLLA/PEG blends after isothermal crystallization at 120℃ for 5 min

Fig.6 Contact angles of PLLA/PEG blends with different composition

Fig.7 Degradation properties of PLLA and PLLA/PEG blends(degradation temperature was 80℃)

Fig.8 Variation of molecular weight and molecular weight distribution of PLLA80PEG20 degraded in 0.5 mol/L HCl solution at different time

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