苯基-低聚倍半硅氧烷和氨基-低聚倍半硅氧烷对左旋聚乳酸结晶行为及热稳定性的影响

以二氯甲烷为溶剂,将不同相对分子质量的左旋聚乳酸（PLLA）与笼型多面体低聚倍半硅氧烷（POSS）进行溶液共混制备POSS/PLLA复合材料。并通过热台偏光显微镜（POM）、DSC、XRD和TGA对POSS/PLLA复合材料和PLLA的结晶形貌、结晶性能和热稳定性进行了表征。结果表明：POSS/PLLA复合材料的结晶温度升高到110℃左右,结晶能力提高;初始热分解温度和终止热分解温度均增大,最大热分解速率对应的温度在373~379℃之间,热稳定性提高。另外,当POSS含量较低时,成核作用占主导地位;而POSS含量较高时,POSS对PLLA分子链运动的阻碍作用逐渐增强。且POSS的阻碍作用对相对分子质量高的PLLA更明显。观察POSS/PLLA复合材料和PLLA的等温结晶形貌,可以看出明显的十字消光现象和环带球晶形貌,另外,球晶在降温过程中会产生裂纹,这与PLLA的脆性有关。     

成核剂TMC-300对聚乳酸耐热性能的影响

用熔融共混法制备了成核剂癸二酸二苯甲酰肼(TMC-300)质量分数分别为0、0.1%、0.2%、0.3%、0.5%的PLLA2003D/TMC-300复合材料。采用偏光显微镜、差示扫描量热分析、热变形温度、扫描电子显微镜及力学测试等方法研究了PLLA复合材料的结晶性能、热性能和力学性能。结果表明,TMC-300的异相成核作用显著,复合材料的结晶度随着TMC-300含量的增加而大幅度增大。当加入质量分数0.5%的TMC-300时,PLLA 2003D的结晶度由6.00%提高到41.27%。含0.5%TMC-300的PLLA 2003D/TMC-300复合材料在110℃~120℃热处理5 min,HDT值可达到115.8℃,TMC-300成核剂的加入提高了聚乳酸的耐热性和热稳定性。另外TMC-300成核剂可明显提高PLLA的力学性能,PLLA的拉伸强度和冲击强度都随着成核剂的加入明显提高。当加入0.5%的TMC-300时,PLLA的冲击强度提高49.78%。     

有机苯磷酸钙对聚L-乳酸结晶性能和熔融行为的影响

为拓宽聚乳酸结晶成核剂范畴,以苯磷酸和氯化钙为原料采用溶液法制备得到层间距为1.544 nm的有机苯磷酸钙(CP),再将其添加到聚L-乳酸(PLLA)基体进行非等温结晶性能和熔融行为研究。非等温结晶性能测试显示CP对PLLA具有异相成核作用,能显著提高其结晶性能;0.7%CP对PLLA的结晶成核效应最佳,在1℃/min的降温速率下,可使PLLA的结晶起始温度从105.88℃增加到115.47℃,结晶焓从1.379 J/g提高到33.90 J/g。熔融行为测试表明PLLA/CP材料的熔融双峰遵循熔融―再结晶机理。     

纳米羟基磷灰石/聚乳酸复合材料力学性能

将纳米羟基磷灰石(n-HA)和聚乳酸(PUA)在溶剂中混合,干燥后再采用热压成型工艺制备n-HA/PLLA复合材料.制备过程中n-HA采用F-127和PEG改性处理.拉伸实验发现:n-HA加入PLLA基体中,能提高PLLA的塑性;PEG改性n-HA与PLLA复合力学性能较好,PEG可以改善HA的分散性.扫描电镜图片显示:与PLLA比较,PEG改性n-HA/PLLA复合材料的断裂为韧性断裂,PLLA的断裂接近脆性断裂.     

纳米纤维素晶须增强增韧聚(L-乳酸)复合材料的制备与表征

通过酸解法制备了具有纳米尺寸和一定长径比针棒状的纳米纤维素晶须(NCW),利用NCW表面的羟基引发L-丙交酯开环聚合,合成了表面接枝聚(L-乳酸)(PLLA)链段的接枝纤维素晶须(g-NCW);采用溶液浇铸法制备了PLLA膜以及不同配比的NCW/PLLA和g-NCW/PLLA复合膜。对接枝改性前后的NCW的形貌与性能进行了表征,研究了复合膜的形貌、结晶性能、热稳定性、亲/疏水性和拉伸性能。结果表明:NCW的形貌与结晶性能在接枝改性后变化不大,但在乙醇和PLLA溶液中的分散性得到明显改善;当NCW与L-丙交酯的物质的量之比为1∶5时,g-NCW表面PLLA链段的接枝率约为23.61%。NCW和g-NCW作为异相成核剂,显著提高了PLLA基体的结晶速率;并且,加入晶须改善了材料的亲水性和热稳定性。添加一定量的NCW和g-NCW到PLLA中,可有效增强增韧PLLA基体;随着晶须含量增加,复合膜的拉伸强度和断裂能先增大后下降;当NCW和g-NCW的质量分数为5%时,NCW/PLLA和g-NCW/PLLA复合膜的拉伸强度和断裂能分别达到22.02 MPa和20.01 MPa以及102.39J/m~3和117.83J/m~3,均达到最大值。由于g-NCW在基体中良好的分散性以及与基体间的界面结合,g-NCW/PLLA复合膜的拉伸强度和韧性明显优于相应的纯PLLA和NCW/PLLA膜。     

嵌段齐聚物修饰纳米SiO2对PET结晶性能的影响

采用溶液聚合法在纳米 SiO2表面接枝两种不同性质的齐聚物聚乙二醇(PEG)和聚对苯二甲酸乙二酯低聚物(LMPET),通过 FTIR、1 H-NMR、XPS 和 HR-TEM 对其结构形貌进行表征。采用熔融共混制备 PET 纳米复合材料,并利用 DSC 和 XRD 对改性纳米 SiO2对 PET 结晶性能的影响进行研究。结果表明,LMPET 通过 PEG 成功接枝到 SiO2表面,粒径尺寸为40~50 nm;纳米 SiO2可作为成核剂诱导 PET 的结晶提高结晶速率,当添加量为2%(质量分数)时,结晶温度得到明显提高。     

多壁碳纳米管接枝聚己内酯对聚左旋乳酸结晶行为和热稳定性的影响

通过羟基化多壁碳纳米管（MWCNTs-OH）引发ε-己内酯（ε-CL）开环聚合制备了聚己内酯（PCL）链接枝的MWCNTs-OH（MWCNTs-OH-g-PCL）。利用溶液共混获得具有不同MWCNTs-OH-g-PCL含量的MWCNTs-OH-g-PCL/聚左旋乳酸（PLLA）复合材料。通过FTIR测试发现,MWCNTs-OH-g-PCL在1 720 cm-1附近出现PCL中的羰基（C=O）伸缩振动峰,表明接枝产物合成成功。通过DSC、偏光显微镜（POM）和TGA观察研究了MWCNTs-OH-g-PCL的加入对PLLA均聚物结晶行为和热稳定性的影响。结果表明,由于MWCNTs-OH-g-PCL的异质成核作用及PCL的增塑作用,MWCNTs-OH-g-PCL/PLLA复合材料的结晶度和最佳等温结晶温度增大。MWCNTs-OH-g-PCL中PCL的接枝量为66%,MWCNTs-OH-g-PCL/PLLA复合材料的分解温度提高了约30℃。      

聚L-乳酸/环糊精复合材料性能研究

为制备具有功能性的聚乳酸复合材料,以聚L-乳酸(PLLA)和α-环糊精(α-CD)为原料,通过熔融共混技术制备PLLA/α-CD复合材料。研究结果显示α-CD促进了PLLA的结晶,提高了PLLA的结晶速率,但材料变脆;而PLLA/α-CD复合材料非等温结晶后的熔融行为则地受到降温速率的强烈影响,降温速率的增加使得PLLA/α-CD复合材料由单熔融峰转变为双熔融峰。热分解性能研究结果则表明添加α-CD能使PLLA的热分解温度升高。     

Zn_2Al-LDH/聚乳酸复合材料的结晶行为EI北大核心CSCD

利用差示扫描量热法(DSC)和偏光显微镜(POM)研究了Zn、Al层状双金属氢氧化物(Zn2A-l LDH)/聚乳酸(PLLA)纳米复合材料的结晶性能。差示扫描量热(DSC)结果表明,在聚乳酸中加入Zn2A-lLDH,可以提高聚乳酸的结晶温度,加快其结晶速度;在120℃等温结晶时,Zn2A-lLDH可以使聚乳酸的半结晶时间由107s缩短至67s。偏光显微镜(POM)结果显示,在PLLA中加入Zn2A-lLDH,Zn2A-lLDH可以起到成核剂的作用,使PLLA在结晶的过程中晶核数目增加,球晶尺寸降低。     

Zn2Al-LDH/聚乳酸复合材料的结晶行为

利用差示扫描量热法(DSC)和偏光显微镜(POM)研究了Zn、Al层状双金属氢氧化物(Zn2A-l LDH)/聚乳酸(PLLA)纳米复合材料的结晶性能。差示扫描量热(DSC)结果表明,在聚乳酸中加入Zn2A-lLDH,可以提高聚乳酸的结晶温度,加快其结晶速度;在120℃等温结晶时,Zn2A-lLDH可以使聚乳酸的半结晶时间由107s缩短至67s。偏光显微镜(POM)结果显示,在PLLA中加入Zn2A-lLDH,Zn2A-lLDH可以起到成核剂的作用,使PLLA在结晶的过程中晶核数目增加,球晶尺寸降低。     

Preparation,crystallization behaviors,and mechanical properties of biodegradable composites based on poly(L-lactic acid) and recycled carbon fiber

The biodegradable composites based on poly(L-lactic acid) (PLLA) and recycled carbon fiber (RCF) were prepared through melting extrusion. The surface-treatment of RCF with silane coupling agent enhanced the interfacial adhesion between RCF and PLLA, and thus the PLLA/RCF composites achieved a significant improvement in mechanical properties. The morphologies of fracture surfaces indicated that the RCF obtained a homogeneous dispersion in PLLA matrix due to a good interfacial interaction. The investigations on the crystallization behaviors and kinetics demonstrated that the RCF acted as a nucleation agent for the crystallization of PLLA, and the crystallization rate and the nucleation density of PLLA matrix were improved remarkably due to the heterogeneous nucleating effect of RCF in the matrix. These features may be advantageous for the enhancement of mechanical properties, heat resistance, and processability of PLLA-based materials. The PLLA-based composites made from RCF can be used as low cost biodegradable materials for many applications.     

Functionalized cellulose nanocrystals as biobased nucleation agents in poly(l-lactide) (PLLA) – Crystallization and mechanical property effects

The important industrial problem of slow crystallization of poly(l-lactide) (PLLA) is addressed by the use of cellulose nanocrystals as biobased nucleation reagents. Cellulose nanocrystals (CNC) were prepared by acid hydrolysis of cotton and additionally functionalized by partial silylation through reactions with n-dodecyldimethylchlorosilane in toluene. Such silylated cellulose nanocrystals (SCNC) were dispersible in tetrahydrofuran and chloroform, and formed stable suspensions. Nanocomposite films of PLLA and CNC or SCNC were prepared by solution casting. The effects of surface silylation of cellulose nanocrystals on morphology, non-isothermal and isothermal crystallization behavior, and mechanical properties of these truly nanostructured composites were investigated. The unmodified CNC formed aggregates in the composites, whereas the SCNC were well-dispersed and individualized in PLLA. As a result, the tensile modulus and tensile strength of the PLLA/SCNC nanocomposite films were more than 20% higher than for pure PLLA with only 1 wt.% SCNC, due to crystallinity effects and fine dispersion.     

Preparation and properties of biodegradable poly(L-lactide)/octamethyl-polyhedral oligomeric silsesquioxanes nanocomposites with enhanced crystallization rate via simple melt compounding

Biodegradable poly(l-lactide) (PLLA)/octamethyl-polyhedral oligomeric silsesquioxanes (ome-POSS) nanocomposites were prepared via simple melt compounding at various ome-POSS loadings in this work. Scanning and transmission electron microscopy observations indicate that ome-POSS were homogeneously dispersed in the PLLA matrix. Effect of ome-POSS on the nonisothermal crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology, crystal structure, dynamic mechanical properties, and thermal stability of PLLA in the nanocomposites was investigated in detail. It is found that the presence of ome-POSS enhances both nonisothermal cold and melt crystallization of PLLA in the nanocomposites relative to neat PLLA. The overall isothermal melt crystallization rates are faster in the PLLA/ome-POSS nanocomposites than in neat PLLA and increase with increasing the ome-POSS loading; however, the crystallization mechanism of PLLA remains unchanged. The nucleation density of PLLA spherulites is enhanced, while the crystal structure of PLLA is not modified in the PLLA/ome-POSS nanocomposites. The storage modulus has been apparently improved in the PLLA/ome-POSS nanocomposites with respect to neat PLLA, whereas the glass-transition temperatures vary slightly between neat PLLA and the PLLA/ome-POSS nanocomposites. The thermal stability of PLLA matrix is reduced slightly in the PLLA/ome-POSS nanocomposites.     

有机化蒙脱石填充尼龙66复合物的结晶与热力学行为研究

通过熔融共混法制备了有机化蒙脱石填充的尼龙66复合材料,通过示差扫描量热分析（DSC）,偏光显微镜照片（POM）和动态力学分析（DMA）等手段研究了复合材料的非等温结晶过程,结晶形态和球晶尺寸,动态力学行为等,并与普通尼龙66进行了比较,发现经过有机化蒙脱石填充的尼龙66的结晶速率比较快,球晶尺寸较小,弹性模量较大。     

反应挤出纳米类水滑石/尼龙6复合材料的结构与性能

采用自制的双甲氧基苯甲酸根离子柱撑镁铝类水滑石(MgAl-HTlcs)和己内酰胺(CL)为主要原料,利用反应挤出工艺制备了纳米MgAl-HTlcs/尼龙6复合材料,研究了MgAl-HTlcs含量对复合材料结构与性能的影响。TEM照片显示:MgAl-HTlcs在复合材料中呈纳米级均匀分散,当MgAl-HTlcs含量为1.0wt%(占MgAl-HTlcs与CL总质量的质量分数)时出现了部分片层剥离的类水滑石。紫外光谱结果表明:与纯尼龙6相比,少量均匀分散的MgAl-HTlcs使复合材料对近紫外波长为320~380nm的紫外线吸收效果明显。XRD和DSC结果表明:少量均匀分散的MgAl-HTlcs对尼龙6起到了很好的异相成核剂的作用,不仅提高了其结晶温度,也增加了其结晶度。热重分析显示:部分片层剥离MgAl-HTlcs的存在明显提高了复合材料的热稳定性。     

Nucleation and crystal growth kinetics of poly(l-lactic acid) with self-assembled DBS nanofibrils

The effect of 1,3:2,4-dibenzylidene-d-sorbitol (DBS) on the crystallization behaviors of poly(l-lactic acid) (PLLA) was examined in this study. A small amount (≤4 wt%) of DBS altered the crystallization rate and regime transition temperature of PLLA. First, the addition of DBS and the formation of self-assembled DBS nanofibrils both increased the nucleation rate of PLLA. Second, the curves of the spherulitic growth rate versus the crystallization temperature of PLLA were discontinuous and did not show the typical bell-shaped behavior for all samples. We found that the change in crystal structures (α′-to-α) affected the regime transition temperatures, which led to the discontinuity. The regime transition (regime II–III) temperatures of PLLA slightly decreased as the DBS amounts were increased. This indicates that the more regular structure (regime II) of PLLA formed at lower temperatures when more DBS was added. In addition, the spherulitic growth rate of PLLA was found to be mainly influenced by the fold surface free energy. When the DBS amounts were increased, the increase in the fold surface free energy decreased the growth rate of PLLA. Nonetheless, the Avrami exponent, n, was not significantly changed because the spherulitic growth geometry and nucleation mechanism of PLLA were basically the same. The Avrami plot also shows that the secondary crystallization began earlier due to the formation of DBS nanofibrils for the samples containing higher DBS amounts.     

Enhanced thermal conductivity of poly(L-lactide) composites with synergistic effect of aluminum nitride and modified multi-walled carbon nanotubes

Poly (ethylene glycol)-grafted multi-walled carbon nanotubes (PEG-MWNTs) were prepared and added into poly(L-lactide) (PLLA)/aluminum nitride (AlN) composites to obtain PLLA/AlN/PEG-MWNTs nanocomposites. Microstructure and thermal conductivity of the composites were investigated on the basis of the influence of PEG-MWNTs incorporated. The results showed that PEG-MWNTs were well-dispersed in the PLLA matrix and had strong interfacial adhesion with the matrix. The addition of PEG-MWNTs improved the thermal conductivity of PLLA/AlN composites. When 3 wt.% of PEG-MWNTs and 50 wt.% of AlN were both added into the PLLA matrix, the thermal conductivity reached 0.7734 W/mK with enhancement almost by 400% as compared to a neat PLLA. However, the thermal conductivity is 0.3401 W/mK for the PLLA composite with 3 wt.% of PEG-MWNTs and 0.4286 W/mK for the one with 50 wt.% of AlN. The synergistic effect of aggregated AlN particles and well-dispersed MWNTs could form efficient thermal conductive paths for improving the thermal conductivity of PLLA composites greatly.     

聚乳酸单轴拉伸膜的包装特性研究

目的研究了不同拉伸比的PLLA薄膜的热学性能、阻隔性能和热收缩性能。方法采用双螺杆挤流延试验机单轴拉伸制备了不同拉伸比的PLLA热收缩膜和定向拉伸膜,采用差示扫描量热分析仪(DSC)、透湿仪和透氧仪对不同拉伸比的PLLA薄膜的热学性能和阻隔性能进行了评估,并对PLLA膜的热收缩性进行了测定。结果热收缩膜的拉伸比由1增大到6.5时,PLLA的结晶度由0.2%增加到41.8%,结晶速率明显提高,阻隔性得到了一定的改善。随着拉伸比例的增大,热收缩率随之增大。定向拉伸膜的结晶度得到了大幅度提高,其阻隔性也得到了改善,但不呈现热收缩性。结论通过单轴拉伸可以有效地提高PLLA薄膜的结晶速率和结晶度,经过中等拉伸比例的PLLA薄膜,其阻湿阻氧能力相对较强。