原位熔融/固相缩聚制备聚乳酸/SiO_2纳米复合材料
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摘要
聚乳酸(Polylactic acid,PLA)是一种非常重要的生物基可生物降解绿色高分子材料,来自自然界使用后又回归自然界。其具有良好的生物降解性和生物相容性,可广泛应用于包装材料、纤维、日用塑料、生物医用材料等领域,但其结晶速率低,耐热性、抗冲击性较差,在应用上受到限制。一般通过共聚、共混、纳米复合等手段对其进行改性,其中纳米粒子分散均匀的纳米复合改性具有较好的改性效果。
本文综述了聚乳酸及其纳米复合材料的合成方法及发展历史,提出了原位熔融／固相缩聚制备聚乳酸/SiO2(PLLA/SiO2)纳米复合材料的方法。
对原位熔融缩聚—脱水/齐聚过程的稳定性进行了研究和改进,对纳米粒子的分散稳定性进行了合理的解释。在原位熔融缩聚前期,反应体系依靠双电层提供的静电作用能使纳米粒子保持稳定均匀分散；熔融缩聚后期,纳米粒子表面吸附的乳酸齐聚物链提供的空间位阻作用能保持纳米粒子稳定均匀分散；而在熔融缩聚过程中,存在一段稳定作用能过渡的薄弱阶段,极易引起纳米粒子聚并形成软团聚或硬团聚。在此阶段,对于纳米粒子含量较低的体系(<5-10%),软团聚的纳米粒子在合适的搅拌条件(φSiO2=5%时,弧形桨,400rpm;φSiO2=10%时,弧形桨,600rpm)下能够被重新分散,最终制得纳米粒子分散均匀的PLLA/Si02纳米复合材料。但是当Si02纳米粒子含量较高(≥20%)或者搅拌条件不合适时,纳米粒子间势能将越过稳定势垒使软团聚的纳米粒子形成不可逆的硬团聚,严重的硬团聚将导致体系凝胶化。
制备了不同分子量、不同Si02纳米粒子含量的PLLA/SiO2纳米复合预聚物,采用DSC对其等温冷结晶和等温热结晶及熔融行为进行了研究。(1).考察了基体分子量对PLLA纳米复合材料等温冷结晶的影响,结晶速率随分子量的升高先增大后减小,当Mw=1.5万时,PLLA/SiO2(φSi,p=5.5%)纳米复合预聚物的结晶速率达到峰值,当Mw≥4万时,结晶速率趋于不变。相比纯PLLA,复合材料的结晶速率升高,达到结晶速率峰值的分子量降低。(2).考察了Si02纳米粒子含量对PLLA/SiO2(Mw≈4万)纳米复合预聚物等温冷结晶的影响,随纳米粒子含量在0-8%内升高,结晶速率逐渐升高,且高温区升高较明显,结晶度先升高后逐渐降低,且低温区影响较明显。(3).考察了Si02纳米粒子含量对PLLA/SiO2(Mw≈4万)纳米复合预聚物等温热结晶的影响,随纳米粒子含量升高,结晶速率逐渐升高,结晶度逐渐降低。另外,不同温度下热结晶得到的晶型不同,等温热结晶温度为95-100℃时存在晶型转变。(4).对等温冷结晶和等温热结晶性能进行了比较,等温冷结晶速率明显高于等温热结晶速率,最快冷结晶速率时的结晶温度(120℃)高于最快热结晶速率时的结晶温度(110℃),但等温结晶方式对结晶度没有明显影响。(5).等温冷结晶和等温热结晶后的熔融行为较类似,熔融峰经历“双熔融峰-单熔融峰”变化,低熔融峰峰面积慢慢增大,峰值温度慢慢升高,高熔融峰峰面积逐渐减小直至消失,峰值温度基本不变。
通过熔融缩聚制备了Mw约为4万、φSi,p为5.5%的纳米复合材料,分别通过等温冷结晶和等温热结晶处理后,在同样的条件(颗粒粒径0.28-0.5 mm,氮气流量0.04 L·min-1·g-1,固相缩聚程序0-5hr/150℃,5-10hr/155℃,10-20hr/160℃)下进行固相缩聚,考察了预结晶条件对固相缩聚的影响。对于等温冷结晶后的固相缩聚,不同的预结晶温度对固相缩聚结果没有明显影响,固相缩聚产物的Mw较接近,达到10万；对于等温热结晶后的固相缩聚,低温下结晶有利于提高固相缩聚产物分子量,在80℃等温热结晶后固相缩聚产物Mw达12万。随固相缩聚进行,结晶度和熔点逐渐升高,熔点和结晶度最终趋于一致,与预结晶方式和初始结晶度无关。,固相缩聚20 hr后,聚乳酸纳米复合材料基本呈白色,未发生明显变色,且纳米粒子呈纳米级的均匀分散。
Polylactic acid (PLA) is a very important bio-based and biodegradable polymer. Its raw materials come from natural resources and it can go back into the natural after use. Because of the good biodegradability and biocompatibility, it can be widely used in packaging materials, fibers, household plastics, bio-medical materials and other fields. But its crystallization rate is small, and its heat and impact resistances are poor, so it is not good enough for some demanding applications. Therefore, it is often modified by means of copolymerization, blending and nano-compositing, etc. PLLA nanocomposites often possess much better properties if the nanoparticles were well-dispersed and appropriate inter-phase interaction is introduced.
This article reviewed the synthesis and modification of PLLA and PLLA nanocomposites, based on which in situ melt/solid state polycondensation of LLA in the presence of acidic silica sol(aSS) has been proposed to prepare PLLA/SiO2 nanocomposites.
The stability of nanoparticles during the D/O stage was studied and improved, and dispersion stability of SiO2 nanoparticles was interpreted theoretically and experimentally.The electrical double-layer and the grafted OLLA chains provide static and steric stabilities at the early and late phases respectively. But there exists a intermediate transitional phase with weak stability when the static stability is weakened but sufficient steric stability has not yet established, leading to "soft" or "hard" aggregation depending on the SiO2 loading and agitation conditions. At low or moderate SiO2 loading (<5-10%), the "soft" aggregation can be depressed with appropriate agitation condition and re-dispersed with the aid of gradually established steric interaction energy resulting from growing grafting. The appropriate agitation energy to stabilize the nanoparticles depends on the SiO2 loading. Well dispersed PLLA/SiO2 nanocomposites with 5% and 10% SiO2 loading were successfully prepared in-situ melt polycondensation using arc stirrer at 400 rpm and 600 rpm respectively in D/O stage. But at high SiO2 loading (≥20%) or improper agitation condition, the nanoparticles are prone to form "hard" aggregation or gel which can not be re-dispersed.
PLLA/SiO2 nanocomposites with different Mw(7,000-73,000g/mol) and differentφsi,p (0-7.8%) were prepared and their isothermal cold and melt crystallizations and melting behaviors were studied by DSC. (1) The isothermal cold crystallization rate is greater than pure PLLA and depends on the matrix molecular weight and SiO2 content. It increases and then decreases with increasing Mw, reaching a maximum value at Mw of 15,000 g/mol and then leveling off at Mw≥40,000. And it increases with increasingφSi,p from 0 to 8%, especially at higher temperature range. (2) The isothermal melt crystallization rate increased and the crystallinity decreased withφsi,p increasing. The crystal structure transformed at Tc of 95-100℃. (3) The isothermal cold crystallization rate was significantly higher than the melt isothermal crystallization rate, and the Tc of the greatest cold crystallization rate (120℃) is higher than the Tc of the greatest melt crystallization rate (110℃). But the isothermal crystallization methods had no significant effect on the crystallinity. (4) The melting behavior after isothermal cold crystallization and isothermal melt crystallization was similar. The melting peak experienced "double melting peaks-a single melting peak". The low-melting peak area gradually increased and the peak temperature increased. The high-melting peak area decreased until disappear, and the peak temperature was basically unchanged.
The PLLA/SiO2 prepolymers (φsi,p 5.5%, Mw-40,000 g/mol) prepared by melt polycondensation were isothermally cold-or melt-crystallized and then solid state polycondensed under same conditions (particle size 0.28-0.5 mm, nitrogen flow 0.04 L-min-1·g-1, SSP program 0-5 hr/150℃,5-10 hr/155℃,10-20 hr/160℃). The isothermal cold crystallization Tc had no significant effect on the SSP. SSP after isothermal cold crystallization at various Tc gave products with almost same Mw of about 100,000 g/mol. SSP after isothermal melt crystallization at lower Tc (80℃) gave product with higher Mw of 120,000. The crystallinity and melting temperature of PLLA inceased continuously during SSP. Their evolutions was independent of the pre-crystallization temperature and the initial crystallinity. And PLLA products after SSP for 20 hr had a white color, showing no observable discoloration, and the nanoparticles were uniformly dispersed in nano-scale.
本文综述了聚乳酸及其纳米复合材料的合成方法及发展历史,提出了原位熔融／固相缩聚制备聚乳酸/SiO2(PLLA/SiO2)纳米复合材料的方法。
对原位熔融缩聚—脱水/齐聚过程的稳定性进行了研究和改进,对纳米粒子的分散稳定性进行了合理的解释。在原位熔融缩聚前期,反应体系依靠双电层提供的静电作用能使纳米粒子保持稳定均匀分散；熔融缩聚后期,纳米粒子表面吸附的乳酸齐聚物链提供的空间位阻作用能保持纳米粒子稳定均匀分散；而在熔融缩聚过程中,存在一段稳定作用能过渡的薄弱阶段,极易引起纳米粒子聚并形成软团聚或硬团聚。在此阶段,对于纳米粒子含量较低的体系(<5-10%),软团聚的纳米粒子在合适的搅拌条件(φSiO2=5%时,弧形桨,400rpm;φSiO2=10%时,弧形桨,600rpm)下能够被重新分散,最终制得纳米粒子分散均匀的PLLA/Si02纳米复合材料。但是当Si02纳米粒子含量较高(≥20%)或者搅拌条件不合适时,纳米粒子间势能将越过稳定势垒使软团聚的纳米粒子形成不可逆的硬团聚,严重的硬团聚将导致体系凝胶化。
制备了不同分子量、不同Si02纳米粒子含量的PLLA/SiO2纳米复合预聚物,采用DSC对其等温冷结晶和等温热结晶及熔融行为进行了研究。(1).考察了基体分子量对PLLA纳米复合材料等温冷结晶的影响,结晶速率随分子量的升高先增大后减小,当Mw=1.5万时,PLLA/SiO2(φSi,p=5.5%)纳米复合预聚物的结晶速率达到峰值,当Mw≥4万时,结晶速率趋于不变。相比纯PLLA,复合材料的结晶速率升高,达到结晶速率峰值的分子量降低。(2).考察了Si02纳米粒子含量对PLLA/SiO2(Mw≈4万)纳米复合预聚物等温冷结晶的影响,随纳米粒子含量在0-8%内升高,结晶速率逐渐升高,且高温区升高较明显,结晶度先升高后逐渐降低,且低温区影响较明显。(3).考察了Si02纳米粒子含量对PLLA/SiO2(Mw≈4万)纳米复合预聚物等温热结晶的影响,随纳米粒子含量升高,结晶速率逐渐升高,结晶度逐渐降低。另外,不同温度下热结晶得到的晶型不同,等温热结晶温度为95-100℃时存在晶型转变。(4).对等温冷结晶和等温热结晶性能进行了比较,等温冷结晶速率明显高于等温热结晶速率,最快冷结晶速率时的结晶温度(120℃)高于最快热结晶速率时的结晶温度(110℃),但等温结晶方式对结晶度没有明显影响。(5).等温冷结晶和等温热结晶后的熔融行为较类似,熔融峰经历“双熔融峰-单熔融峰”变化,低熔融峰峰面积慢慢增大,峰值温度慢慢升高,高熔融峰峰面积逐渐减小直至消失,峰值温度基本不变。
通过熔融缩聚制备了Mw约为4万、φSi,p为5.5%的纳米复合材料,分别通过等温冷结晶和等温热结晶处理后,在同样的条件(颗粒粒径0.28-0.5 mm,氮气流量0.04 L·min-1·g-1,固相缩聚程序0-5hr/150℃,5-10hr/155℃,10-20hr/160℃)下进行固相缩聚,考察了预结晶条件对固相缩聚的影响。对于等温冷结晶后的固相缩聚,不同的预结晶温度对固相缩聚结果没有明显影响,固相缩聚产物的Mw较接近,达到10万；对于等温热结晶后的固相缩聚,低温下结晶有利于提高固相缩聚产物分子量,在80℃等温热结晶后固相缩聚产物Mw达12万。随固相缩聚进行,结晶度和熔点逐渐升高,熔点和结晶度最终趋于一致,与预结晶方式和初始结晶度无关。,固相缩聚20 hr后,聚乳酸纳米复合材料基本呈白色,未发生明显变色,且纳米粒子呈纳米级的均匀分散。
Polylactic acid (PLA) is a very important bio-based and biodegradable polymer. Its raw materials come from natural resources and it can go back into the natural after use. Because of the good biodegradability and biocompatibility, it can be widely used in packaging materials, fibers, household plastics, bio-medical materials and other fields. But its crystallization rate is small, and its heat and impact resistances are poor, so it is not good enough for some demanding applications. Therefore, it is often modified by means of copolymerization, blending and nano-compositing, etc. PLLA nanocomposites often possess much better properties if the nanoparticles were well-dispersed and appropriate inter-phase interaction is introduced.
This article reviewed the synthesis and modification of PLLA and PLLA nanocomposites, based on which in situ melt/solid state polycondensation of LLA in the presence of acidic silica sol(aSS) has been proposed to prepare PLLA/SiO2 nanocomposites.
The stability of nanoparticles during the D/O stage was studied and improved, and dispersion stability of SiO2 nanoparticles was interpreted theoretically and experimentally.The electrical double-layer and the grafted OLLA chains provide static and steric stabilities at the early and late phases respectively. But there exists a intermediate transitional phase with weak stability when the static stability is weakened but sufficient steric stability has not yet established, leading to "soft" or "hard" aggregation depending on the SiO2 loading and agitation conditions. At low or moderate SiO2 loading (<5-10%), the "soft" aggregation can be depressed with appropriate agitation condition and re-dispersed with the aid of gradually established steric interaction energy resulting from growing grafting. The appropriate agitation energy to stabilize the nanoparticles depends on the SiO2 loading. Well dispersed PLLA/SiO2 nanocomposites with 5% and 10% SiO2 loading were successfully prepared in-situ melt polycondensation using arc stirrer at 400 rpm and 600 rpm respectively in D/O stage. But at high SiO2 loading (≥20%) or improper agitation condition, the nanoparticles are prone to form "hard" aggregation or gel which can not be re-dispersed.
PLLA/SiO2 nanocomposites with different Mw(7,000-73,000g/mol) and differentφsi,p (0-7.8%) were prepared and their isothermal cold and melt crystallizations and melting behaviors were studied by DSC. (1) The isothermal cold crystallization rate is greater than pure PLLA and depends on the matrix molecular weight and SiO2 content. It increases and then decreases with increasing Mw, reaching a maximum value at Mw of 15,000 g/mol and then leveling off at Mw≥40,000. And it increases with increasingφSi,p from 0 to 8%, especially at higher temperature range. (2) The isothermal melt crystallization rate increased and the crystallinity decreased withφsi,p increasing. The crystal structure transformed at Tc of 95-100℃. (3) The isothermal cold crystallization rate was significantly higher than the melt isothermal crystallization rate, and the Tc of the greatest cold crystallization rate (120℃) is higher than the Tc of the greatest melt crystallization rate (110℃). But the isothermal crystallization methods had no significant effect on the crystallinity. (4) The melting behavior after isothermal cold crystallization and isothermal melt crystallization was similar. The melting peak experienced "double melting peaks-a single melting peak". The low-melting peak area gradually increased and the peak temperature increased. The high-melting peak area decreased until disappear, and the peak temperature was basically unchanged.
The PLLA/SiO2 prepolymers (φsi,p 5.5%, Mw-40,000 g/mol) prepared by melt polycondensation were isothermally cold-or melt-crystallized and then solid state polycondensed under same conditions (particle size 0.28-0.5 mm, nitrogen flow 0.04 L-min-1·g-1, SSP program 0-5 hr/150℃,5-10 hr/155℃,10-20 hr/160℃). The isothermal cold crystallization Tc had no significant effect on the SSP. SSP after isothermal cold crystallization at various Tc gave products with almost same Mw of about 100,000 g/mol. SSP after isothermal melt crystallization at lower Tc (80℃) gave product with higher Mw of 120,000. The crystallinity and melting temperature of PLLA inceased continuously during SSP. Their evolutions was independent of the pre-crystallization temperature and the initial crystallinity. And PLLA products after SSP for 20 hr had a white color, showing no observable discoloration, and the nanoparticles were uniformly dispersed in nano-scale.
引文
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29 Pluta M, Galeski A, Alexandre M, et al. Polylactide/Montmorillonite Nanocomposites and Microcomposites Prepared by Melt Blending:Structure and some Physical Properties[J]. J Appl Polym Sci.2002,86(6):1497-1506.
30康宏亮,陈成,庄宇刚,等.聚乳酸／蒙脱土纳米复合材料的结构和热性能[J].应用化学.2005(3)：346-348.
31 Kubies D, Scudla J, Puffr R, et al. Structure and Mechanical Properties of Poly(L-Lactide)/Layered Silicate Nanocomposites[J]. Eur Polym J.2006,42(4):888-899.
32 Chen G X, Kim H S, Shim J H, et al. Role of Epoxy Groups On Clay Surface in the Improvement of Morphology of Poly(L-Lactide)/Clay Composites[J]. Macromolecules.2005, 38(9):3738-3744.
33 Paul M A, Alexandre M, Degee P, et al. Exfoliated Polylactide/Clay Nanocomposites by in-Situ Coordination-Insertion Polymerization[J]. Macromol Rapid Comm.2003,24(9): 561-566.
34 Paul M A, Delcourt C, Alexandre M, et al. (Plasticized) Polylactide/(Organo-)Clay Nanocomposites by in Situ Intercalative Polymerization[J]. Macromol Chem Phys.2005, 206(4):484-498.
35 Garlotta D. A Literature Review of Poly(Lactic Acid)[J]. J Polym Environ.2001,9(2):63-84.
36 Brandao L S, Mendes L C, Medeiros M E, et al. Thermal and Mechanical Properties of Poly(Ethylene Terephthalate)/Lamellar Zirconium Phosphate Nanocomposites[M]. HOBOKEN:2006:3868-3876.
37 Pan P. Morphology, and Physical Properties of Poly(Lactide) and its Composite Materials[D]. Biomolecular Engineering Tokyo Institute of Technology,2008.
38 Moon S I, Jin F, Lee C, et al. Novel Carbon Nanotube/Poly(L-Lactic Acid) Nanocomposites; Their Modulus, Thermal Stability, and Electrical Conductivity[J]. Macromol Symp.2005,224: 287-295.
39 Chen G X, Kim H S, Park B H, et al. Controlled Functionalization of Multiwalled Carbon Nanotubes with Various Molecular-Weight Poly(L-Lactic Acid)[J]. J Phys Chem B.2005, 109(47):22237-22243.
40 Hong Z K, Zhang P B, He C L, et al. Nano-Composite of Poly(L-Lactide) and Surface Grafted Hydroxyapatite:Mechanical Properties and Biocompatibility[J]. Biomaterials.2005,26(32): 6296-6304.
41 Qiu X Y, Hong Z K, Hu J L, et al. Hydroxyapatite Surface Modified by L-Lactic Acid and its Subsequent Grafting Polymerization of L-Lactide[J]. Biomacromolecules.2005,6(3): 1193-1199.
42 Yan S F, Yin J B, Yang Y, et al. Surface-Grafted Silica Linked with L-Lactic Acid Oligomer: A Novel Nanofiller to Improve the Performance of Biodegradable Poly(L-Lactide)[J]. Polymer.2007,48(6):1688-1694.
43 Joubert M, Delaite C, Bourgeat-Lami E, et al. Ring-Opening Polymerization of Epsilon-Caprolactone and L-Lactide From Silica Nanoparticles Surface[J]. J Polym Sci Pol Chem.2004,42(8):1976-1984.
44 Carrot G, Rutot-Houze D, Pottier A, et al. Surface-Initiated Ring-Opening Polymerization:A Versatile Method for Nanoparticle Ordering[J]. Macromolecules.2002,35(22):8400-8404.
45周海鸥,史铁钧,王华林,等.聚乳酸／二氧化硅有机无机杂化材料的制备和表征[J].高分子材料科学与工程.2006(2):220-222.
46曹丹.聚乳酸/SiO_2纳米复合材料的原位缩聚法制备与表征[D].浙江大学,2007.
47 Espartero J L, Rashkov I, Li S M, et al. Nmr Analysis of Low Molecular Weight Poly(Lactic Acid)S[J]. Macromolecules.1996,29:3535-3539.
48 Xu G L, Zhang J J, Song G Z. Effect of Complexation On the Zeta Potential of Silica Powder[J]. Powder Technol.2003,134:218-222.
49 Sadasivan S, Rasmussen D H, Chen F P, et al. Preparation and Characterization of Ultrafine Silica[J]. Colloid Surface a.1998,132:45-52.
50 Tourbin M, Frances C. A Survey of Complementary Methods for the Characterization of Dense Colloidal Silica[J]. PARTICLE.2007,24:411-423.
51 Wu L, Cao D, Huang Y, et al. Poly(L-Lactic Acid)/Sio2 Nanocomposites Via in Situ Melt Polycondensation of L-Lactic Acid in the Presence of Acidic Silica Sol:Preparation and Characterization[J]. Polymer.2008,49:742-748.
52 Bikiaris D, Karavelidis V, Karayannidis G. A New Approach to Prepare Poly(Ethylene Terephthalate)/Silica Nanocomposites with Increased Molecular Weight and Fully Adjustable Branching Or Crosslinking by Ssp[J]. Macromol Rapid Comm.2006,27:1199-1205.
53 Yao X, Tian X, Xie D, et al. Interface Structure of Poly (Ethyl ene Terephthalate)/Silica Nanocomposites[J]. Polymer.2009,50:1251-1256.
54 Shin Y, Lee D, Lee K, et al. Surface Properties of Silica Nanoparticles Modified with Polymers for Polymer Nanocomposite Applications[J]. J Ind Eng Chem.2008,14:515-519.
55 Pham K N, Fullston D, Sagoe-Crentsil K. Surface Modification for Stability of Nano-Sized Silica Colloids (Retraction Article. See Vol.342, Pg.643,2010)[J]. J Colloid Interf Sci.2007, 315:123-127.
56 Jesionowski T, Zurawska J, Krysztafkiewicz A. Surface Properties and Dispersion Behaviour of Precipitated Silicas[J]. J Mater Sci.2002,37:1621-1633.
57 Miyata T, Masuko T. Crystallization Behaviour of Poly(L-Lactide)[J]. Polymer.1998,39(22): 5515-5521.
58 Pan P, Kai W, Zhu B, et al. Polymorphous Crystallization and Multiple Melting Behavior of Poly(L-Lactide):Molecular Weight Dependence[J]. Macromolecules.2007,40:6898-6905.
59 Tsujia H, Ikadab Y. Stereocomplex Formation Between Enantiomeric Poly(Lactic Acid)S. Xi. Mechanical Properties and Morphology of Solution-Cast Films[J]. Polymer.1999,40: 6699-6708.
60 Pan P, Zhu B, Kai W, et al. Effect of Crystallization Temperature On Crystal Modifications and Crystallization Kinetics of Poly(L-Lactide)[J]. J Appl Polym Sci.2008,107:54-62.
61 Kawai T, Rahman N, Matsuba G, et al. Crystallization and Melting Behavior of Poly (L-Lactic Acid)[J]. Macromolecules.2007,40:9463-9469.
62 Yasuniwa M, Tsubakihara S, lura K, et al. Crystallization Behavior of Poly(L-Lactic Acid)[J]. Polymer.2006,47:7554-7563.
63 Annette C, Renouf-Glausera, Roseb J, et al. The Effect of Crystallinity On the Deformation Mechanism and Bulk Mechanical Properties of Plla[J]. Biomaterials.2005,26:5771-5782.
64 Iannacea S, Maffezzolib A, Leoc G, et al. Influence of Crystal and Amorphous Phase Morphology On Hydrolytic Degradation of Plla Subjected to Different Processing Conditions[J]. Polymer.2001,42:3799-3807.
65 Yu L, Liu H, Dean K, et al. Cold Crystallization and Postmelting Crystallization of Pla Plasticized by Compressed Carbon Dioxide[J]. J Polym Sci Pol Phys.2008,46:2630-2636.
66 Fujimori A, Ninomiya N, Masuko T. Influence of Dispersed Organophilic Montmorillonite at Nanorneter-Scale On Crystallization of Poly(L-Lactide)[J]. Polym Eng Sci.2008,48: 1103-1111.
67 Pan P, Zhu B, Kai W, et al. Crystallization Behavior and Mechanical Properties of Bio-Based Green Composites Based On Poly(L-Lactide) and Kenaf Fiber[J]. J Appl Polym Sci.2007, 105:1511-1520.
68 Yasuniwa M, Tsubakihara S, lura K, et al. Crystallization Behavior of Poly(L-Lactic Acid)[J]. Polymer.2006,47(21):7554-7563.
69 Yasuniwa M, Lura K, Dan Y. Melting Behavior of Poly(L-Lactic Acid):Effects of Crystallization Temperature and[J]. Polymer.2007,48(18):5398-5407.
70 Xu H, Luo M H, Yu M H, et al. The Effect of Crystallization On the Solid State Polycondensation of Poly(L-Lactic Acid)[C].2006.681-687.
71 R N, James C, Ramesh S, et al. Development of Structure and Morphology During Crystallization and Solid State Polymerization of Polyester Oligomers[J]. Macromol Chem Phys.2001,202:1200-1206.
72 Yu H, Han K H, Yu M H. The Rate Acceleration in Solid-State Polycondensation of Pet by Nanomaterials[J]. J Appl Polym Sci.2004,94:971-976.
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26 Ray S S, Okamoto M. Polymer/Layered Silicate Nanocomposites:A Review From Preparation to Processing[J]. Prog Polym Sci.2003,28(11):1539-1641.
27 Pluta M, Galeski A, Alexandre M, et al. Polylactide/Montmorillonite Nanocomposites and Microcomposites Prepared by Melt Blending:Structure and some Physical Properties[J]. J Appl Polym Sci.2002,86(6):1497-1506.
28 Ogata N, Jimenez G, Kawai H, et al. Structure and Thermal/Mechanical Properties of Poly(L-Lactide)-Clay Blend[J]. Journal of Polymer Science Part B:Polymer Physics.1997, 35(2):389-396.
29 Pluta M, Galeski A, Alexandre M, et al. Polylactide/Montmorillonite Nanocomposites and Microcomposites Prepared by Melt Blending:Structure and some Physical Properties[J]. J Appl Polym Sci.2002,86(6):1497-1506.
30康宏亮,陈成,庄宇刚,等.聚乳酸／蒙脱土纳米复合材料的结构和热性能[J].应用化学.2005(3)：346-348.
31 Kubies D, Scudla J, Puffr R, et al. Structure and Mechanical Properties of Poly(L-Lactide)/Layered Silicate Nanocomposites[J]. Eur Polym J.2006,42(4):888-899.
32 Chen G X, Kim H S, Shim J H, et al. Role of Epoxy Groups On Clay Surface in the Improvement of Morphology of Poly(L-Lactide)/Clay Composites[J]. Macromolecules.2005, 38(9):3738-3744.
33 Paul M A, Alexandre M, Degee P, et al. Exfoliated Polylactide/Clay Nanocomposites by in-Situ Coordination-Insertion Polymerization[J]. Macromol Rapid Comm.2003,24(9): 561-566.
34 Paul M A, Delcourt C, Alexandre M, et al. (Plasticized) Polylactide/(Organo-)Clay Nanocomposites by in Situ Intercalative Polymerization[J]. Macromol Chem Phys.2005, 206(4):484-498.
35 Garlotta D. A Literature Review of Poly(Lactic Acid)[J]. J Polym Environ.2001,9(2):63-84.
36 Brandao L S, Mendes L C, Medeiros M E, et al. Thermal and Mechanical Properties of Poly(Ethylene Terephthalate)/Lamellar Zirconium Phosphate Nanocomposites[M]. HOBOKEN:2006:3868-3876.
37 Pan P. Morphology, and Physical Properties of Poly(Lactide) and its Composite Materials[D]. Biomolecular Engineering Tokyo Institute of Technology,2008.
38 Moon S I, Jin F, Lee C, et al. Novel Carbon Nanotube/Poly(L-Lactic Acid) Nanocomposites; Their Modulus, Thermal Stability, and Electrical Conductivity[J]. Macromol Symp.2005,224: 287-295.
39 Chen G X, Kim H S, Park B H, et al. Controlled Functionalization of Multiwalled Carbon Nanotubes with Various Molecular-Weight Poly(L-Lactic Acid)[J]. J Phys Chem B.2005, 109(47):22237-22243.
40 Hong Z K, Zhang P B, He C L, et al. Nano-Composite of Poly(L-Lactide) and Surface Grafted Hydroxyapatite:Mechanical Properties and Biocompatibility[J]. Biomaterials.2005,26(32): 6296-6304.
41 Qiu X Y, Hong Z K, Hu J L, et al. Hydroxyapatite Surface Modified by L-Lactic Acid and its Subsequent Grafting Polymerization of L-Lactide[J]. Biomacromolecules.2005,6(3): 1193-1199.
42 Yan S F, Yin J B, Yang Y, et al. Surface-Grafted Silica Linked with L-Lactic Acid Oligomer: A Novel Nanofiller to Improve the Performance of Biodegradable Poly(L-Lactide)[J]. Polymer.2007,48(6):1688-1694.
43 Joubert M, Delaite C, Bourgeat-Lami E, et al. Ring-Opening Polymerization of Epsilon-Caprolactone and L-Lactide From Silica Nanoparticles Surface[J]. J Polym Sci Pol Chem.2004,42(8):1976-1984.
44 Carrot G, Rutot-Houze D, Pottier A, et al. Surface-Initiated Ring-Opening Polymerization:A Versatile Method for Nanoparticle Ordering[J]. Macromolecules.2002,35(22):8400-8404.
45周海鸥,史铁钧,王华林,等.聚乳酸／二氧化硅有机无机杂化材料的制备和表征[J].高分子材料科学与工程.2006(2):220-222.
46曹丹.聚乳酸/SiO_2纳米复合材料的原位缩聚法制备与表征[D].浙江大学,2007.
47 Espartero J L, Rashkov I, Li S M, et al. Nmr Analysis of Low Molecular Weight Poly(Lactic Acid)S[J]. Macromolecules.1996,29:3535-3539.
48 Xu G L, Zhang J J, Song G Z. Effect of Complexation On the Zeta Potential of Silica Powder[J]. Powder Technol.2003,134:218-222.
49 Sadasivan S, Rasmussen D H, Chen F P, et al. Preparation and Characterization of Ultrafine Silica[J]. Colloid Surface a.1998,132:45-52.
50 Tourbin M, Frances C. A Survey of Complementary Methods for the Characterization of Dense Colloidal Silica[J]. PARTICLE.2007,24:411-423.
51 Wu L, Cao D, Huang Y, et al. Poly(L-Lactic Acid)/Sio2 Nanocomposites Via in Situ Melt Polycondensation of L-Lactic Acid in the Presence of Acidic Silica Sol:Preparation and Characterization[J]. Polymer.2008,49:742-748.
52 Bikiaris D, Karavelidis V, Karayannidis G. A New Approach to Prepare Poly(Ethylene Terephthalate)/Silica Nanocomposites with Increased Molecular Weight and Fully Adjustable Branching Or Crosslinking by Ssp[J]. Macromol Rapid Comm.2006,27:1199-1205.
53 Yao X, Tian X, Xie D, et al. Interface Structure of Poly (Ethyl ene Terephthalate)/Silica Nanocomposites[J]. Polymer.2009,50:1251-1256.
54 Shin Y, Lee D, Lee K, et al. Surface Properties of Silica Nanoparticles Modified with Polymers for Polymer Nanocomposite Applications[J]. J Ind Eng Chem.2008,14:515-519.
55 Pham K N, Fullston D, Sagoe-Crentsil K. Surface Modification for Stability of Nano-Sized Silica Colloids (Retraction Article. See Vol.342, Pg.643,2010)[J]. J Colloid Interf Sci.2007, 315:123-127.
56 Jesionowski T, Zurawska J, Krysztafkiewicz A. Surface Properties and Dispersion Behaviour of Precipitated Silicas[J]. J Mater Sci.2002,37:1621-1633.
57 Miyata T, Masuko T. Crystallization Behaviour of Poly(L-Lactide)[J]. Polymer.1998,39(22): 5515-5521.
58 Pan P, Kai W, Zhu B, et al. Polymorphous Crystallization and Multiple Melting Behavior of Poly(L-Lactide):Molecular Weight Dependence[J]. Macromolecules.2007,40:6898-6905.
59 Tsujia H, Ikadab Y. Stereocomplex Formation Between Enantiomeric Poly(Lactic Acid)S. Xi. Mechanical Properties and Morphology of Solution-Cast Films[J]. Polymer.1999,40: 6699-6708.
60 Pan P, Zhu B, Kai W, et al. Effect of Crystallization Temperature On Crystal Modifications and Crystallization Kinetics of Poly(L-Lactide)[J]. J Appl Polym Sci.2008,107:54-62.
61 Kawai T, Rahman N, Matsuba G, et al. Crystallization and Melting Behavior of Poly (L-Lactic Acid)[J]. Macromolecules.2007,40:9463-9469.
62 Yasuniwa M, Tsubakihara S, lura K, et al. Crystallization Behavior of Poly(L-Lactic Acid)[J]. Polymer.2006,47:7554-7563.
63 Annette C, Renouf-Glausera, Roseb J, et al. The Effect of Crystallinity On the Deformation Mechanism and Bulk Mechanical Properties of Plla[J]. Biomaterials.2005,26:5771-5782.
64 Iannacea S, Maffezzolib A, Leoc G, et al. Influence of Crystal and Amorphous Phase Morphology On Hydrolytic Degradation of Plla Subjected to Different Processing Conditions[J]. Polymer.2001,42:3799-3807.
65 Yu L, Liu H, Dean K, et al. Cold Crystallization and Postmelting Crystallization of Pla Plasticized by Compressed Carbon Dioxide[J]. J Polym Sci Pol Phys.2008,46:2630-2636.
66 Fujimori A, Ninomiya N, Masuko T. Influence of Dispersed Organophilic Montmorillonite at Nanorneter-Scale On Crystallization of Poly(L-Lactide)[J]. Polym Eng Sci.2008,48: 1103-1111.
67 Pan P, Zhu B, Kai W, et al. Crystallization Behavior and Mechanical Properties of Bio-Based Green Composites Based On Poly(L-Lactide) and Kenaf Fiber[J]. J Appl Polym Sci.2007, 105:1511-1520.
68 Yasuniwa M, Tsubakihara S, lura K, et al. Crystallization Behavior of Poly(L-Lactic Acid)[J]. Polymer.2006,47(21):7554-7563.
69 Yasuniwa M, Lura K, Dan Y. Melting Behavior of Poly(L-Lactic Acid):Effects of Crystallization Temperature and[J]. Polymer.2007,48(18):5398-5407.
70 Xu H, Luo M H, Yu M H, et al. The Effect of Crystallization On the Solid State Polycondensation of Poly(L-Lactic Acid)[C].2006.681-687.
71 R N, James C, Ramesh S, et al. Development of Structure and Morphology During Crystallization and Solid State Polymerization of Polyester Oligomers[J]. Macromol Chem Phys.2001,202:1200-1206.
72 Yu H, Han K H, Yu M H. The Rate Acceleration in Solid-State Polycondensation of Pet by Nanomaterials[J]. J Appl Polym Sci.2004,94:971-976.