Structure and performance of poly (lactic acid)/amide ethylenediamine tetraacetic acid disodium salt intercalation layered double hydroxides nanocomposites

Modified layered double hydroxides (E-LDHs) were successfully prepared by the intercalation of ethylenediamine tetraacetic acid disodium salt (EDTA). Then, amide EDTA intercalation layered double hydroxides (AE-LDHs) were synthesized using aniline. The structure characterization of AE-LDHs demonstrated that AE-LDHs was successfully amidified. To enhance the properties of poly (lactic acid) (PLA), PLA/AE-LDHs nanocomposites were prepared by using AE-LDHs as the nucleating agent. Mechanical properties, thermal stabilities and crystallization properties of PLA/AE-LDHs nanocomposites were investigated by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and rheological behavior analysis. Results of mechanical properties and TG analysis showed that mechanical properties, thermal stabilities of PLA/AE-LDHs nanocomposites were improved significantly compared to pure PLA. Differential scanning calorimetry (DSC) demonstrated that AE-LDHs restricted the cold crystallization of PLA matrix and improved the crystallinity of PLA by 30.15%. POM analysis showed that AE-LDHs acted as an excellent nucleating agent, which greatly increased the crystallization rate of PLA. Compared with pure PLA, the maximum torque and apparent viscosity of PLA/AE-LDHs nanocomposites were improved by 46.21% and 85.86%, respectively, which proved that the AE-LDHs increased the rigidity of network structure of PLA matrix. In this work, an efficient and feasible nucleating agent for improving the crystallinity of PLA was presented through the amidation of LDHs.     

Crystallization of poly(lactic acid) enhanced by phthalhydrazide as nucleating agent

The effect of phthalhydrazide compound on the nonisothermal and isothermal crystallization behavior of bio-based and biodegradable poly(lactic acid) (PLA) was investigated by differential scanning calorimetry and polarized optical microscopy. The nonisothermal melt crystallization of PLA started much earlier in the presence of phthalhydrazide even at a phthalhydrazide content as low as 0.1 wt%. The isothermal crystallization kinetics was analyzed by the Avrami model. It was found that the Avrami exponent of the PLA crystallization was not significantly influenced by the addition of phthalhydrazide, indicating that the crystallization mechanism almost did not change in the composites. The crystallization half-time of PLA/phthalhydrazide composites decreased significantly with increase in phthalhydrazide loading. The observation from optical microscopy showed that the presence of phthalhydrazide increased the number of nucleation sites. The above observations indicate that phthalhydrazide is an efficient nucleating agent of PLA.     

Crystallization morphology and crystallization kinetics of poly(lactic acid): effect of <Emphasis Type="Italic">N</Emphasis>-Aminophthalimide as nucleating agent

The effect of N-Aminophthalimide compound (NA-S) as nucleating agent on crystallization behavior and morphology of poly(lactic acid) was studied. With polarized optical microscope (POM), the unique phenomena of nucleation and epitaxial crystallization of PLA/NA-S system were observed. Dynamic morphology of crystallization was also studied by POM to investigate the relationship between growth behavior of PLA and nucleating agent. Isothermal and non-isothermal crystallization behavior of PLA were studied by differential scan calorimeter (DSC). When nucleating agent was added, a new peak appeared in wide angle X-ray diffraction (WAXD) compared with pure PLA, indicating the nucleating effect of NA-S on crystallization of PLA. All the results indicate that the nucleating agent of NA-S shows obvious nucleating effect on isothermal crystallization above 120 °C and in non-isothermal crystallization after it is added in PLA, that is, the induction crystallization time is reduced, the crystallization rate and nucleation density of PLA are increased.     

退火对聚乳酸结晶及耐热性能的影响

以活化海泡石(ADI-S)为成核剂,通过熔融混合的方法制备了聚乳酸(PLA)/ADI-S复合材料。采用差示扫描量热仪、广角X射线衍射仪、偏光显微镜和热变形、维卡软化点温度测定仪分析了退火条件对PLA结晶性能及耐热性能的影响。结果表明,添加成核剂后,短时间内的退火可大幅提高PLA的结晶度和耐热性能;PLA/ADI-S在90 ℃退火10 min时,其结晶度为53.3 %,维卡软化点为83.3 ℃。     

Effect of biobased and biodegradable nucleating agent on the isothermal crystallization of poly(lactic acid)

The effect of chemically modified thermoplastic starch (CMPS) on the thermal properties and isothermal crystallization kinetics of poly(lactic acid) (PLA) was studied by differential scanning calorimetry (DSC) and compared to that of granular starch and an inorganic nucleating agent, talc. Nucleated PLA showed an additional crystallization of PLA, which affected the melting temperature. The crystallinity and crystallization rate of PLA were considerably enhanced by addition of CMPS, even at 0.1% content, and the amount of the CMPS had little effect on the thermal properties and isothermal crystallization kinetics of PLA. The effect of CMPS as a nucleating agent was comparable to that of granular starch but slightly less than that of talc. However, CMPS can offer a fully biodegradable nucleating agent with no residues remaining for the biobased and biodegradable polymers.     

The nucleation effect of modified carbon black on crystallization of poly(lactic acid)

The nonisothermal crystallization of poly(lactic acid) (PLA), PLA/carbon black (CB), and PLA/modified carbon black (MCB) composites were investigated using differential scanning calorimetry (DSC) analysis. The rate of crystallization and the spherulitic morphologies of the PLA and PLA/MCB composites during isothermal crystallization were investigated using DSC and observed by means of polarizing optical microscopy (POM), respectively. The results show that either CB or MCB acts as an efficient nucleating agent for PLA. The nucleation activities of CB and MCB were quantitatively determined. It is shown that MCB has higher nucleating activity than CB in PLA. An isoconversional method correlates the temperature dependence of the effective activation energy and was used to evaluate the effective activation energy of PLA and PLA/MCB composites. It is confirmed that MCB advances the nuclei density and promotes the crystallization rate of the PLA matrix significantly. In addition, an interesting phenomenon of the periodic cracks of PLA spherulites observed by using POM is reported. The unbalanced surface stresses arising from growth features and thermal shrinkage may be the two main factors accounting for the formation of target pattern cracks. POLYM. ENG. SCI., 50:1658–1666, 2010. © 2010 Society of Plastics Engineers     

Non-isothermal crystallization kinetics of poly (lactic acid)/modified carbon black composite

A novel method was employed to modify the surface of carbon black (CB) by an organic small molecule in a Haake Rheomix mixer. Jeziorny equation, the Ozawa model and Mo equation were employed to describe the non-isothermal crystallization process of poly (lactic acid) (PLA), PLA/CB and PLA/modified carbon black (MCB) composites. It is found that the Ozawa model fail to describe the non-isothermal crystallization process for PLA and its composites, while Jeziorny equation and Mo’s theory provide a good fitting. The comparison of crystallization kinetics between PLA/MCB and PLA through Lauritzen–Hoffman model indicates that there appears a transition from regimes II to III in PLA and PLA/MCB. The fold surface free energy σ _e of PLA/MCB composite is higher than that of neat PLA, implying that the existence of nucleating agent is unfavorable for the regular folding of the molecule chain.     

Reinforcing effect of nanocrystalline cellulose and office waste paper fibers on mechanical and thermal properties of poly (lactic acid) composites

Nanocrystalline cellulose (NCC) was prepared from office waste paper (OWP) by sulfuric acid hydrolysis method in this paper and it was used to prepare a series of poly (lactic acid) PLA/NCC composites by using a dissolution method in solvent N, N-dimethylformamide solution. The results indicated that with the addition of only 3 wt% NCC, the composites exhibited outstanding mechanical property. The tensile, bending and impact properties of the PLA/3NCC composite were improved by 8.2%, 13.1%, and 35.9% than those of pure PLA, respectively. On this basis, office waste paper fibers (OWF) were also used as a physical blended filler to enhance PLA/NCC composites to reduce the preparation cost of PLA composites and the perfect PLA/NCC/OWF sample was easily manufactured by melting–blending and injection molding. According to the crystallization and melting performance table, both NCC and OWF can act as nucleating agent to promote the crystallization properties on composites, while the blends did not have positive effect on thermal stability. Furthermore, the water absorption and degradation properties of PLA composites were also studied. This work not only provided a novel idea for the utilization of office waste paper but also successfully produced environment friendly composites with favorable mechanical properties and crystallization performance.     

Study on the mechanical and thermal properties of poly(lactic acid)/office waste paper fiber composites

Environment friendly composites with favorable mechanical properties and low water absorption performance were successfully produced from poly(lactic acid) (PLA), office waste paper fiber (OWF), and coupling agents. The perfect sample was easily manufactured by melting–blending and injection molding. The PLA/OWF composites were comparable with other PLA/plant fiber composites, and the results indicated that the PLA/OWF composites show better performance than PLA/wheat straw fiber composites and PLA/bamboo fiber composites. On this basis, influence of modification of OWF on the properties of composites was investigated. The infrared results show that the OWF modification by different coupling agents was successful, and the scanning electron microscopy indicates that prepared composites exhibit good interfacial compatibility due to preferable binding force between fiber and matrix. With addition of 2 wt% γ-(2,3-propylene oxides)propyl trimethylsilane, the composite exhibits high tensile strength of 58.96 MPa, reflecting increase of 14% than the pure PLA. According to the crystallization and melting performance table, OWF can act as nucleating agent to promote the crystallization properties on composites, while the coupling agents have little effect on thermal stability. This article confirmed that the OWF has appropriate properties and is suitable for preparing composite materials and this work provides a novel idea for the utilization of office waste paper.     

剑麻纤维增强聚乳酸复合材料酶降解研究

通过热压成型的方式制备了剑麻纤维增强聚乳酸（PLA/SF）复合材料,并通过K蛋白酶降解方式研究了该复合材料的生物降解性能,利用差热扫描量热仪测试分析了复合材料在酶降解过程中的非等温结晶性能。研究发现,剑麻纤维的加入加快了聚乳酸及其复合材料的降解速率,且随着剑麻纤维含量的增加,其降解速率提高;剑麻纤维的加入对聚乳酸的结晶性能有一定的影响,进而也影响了复合材料的酶水解速度。     

苯基磷酸锌对聚乳酸结晶行为影响的研究

采用DSC,POM研究了成核剂苯基磷酸锌（PPZn）对聚乳酸结晶行为的影响。结果表明：PPZn可以作为聚乳酸的高效成核剂,PPZn的加入显著提高了聚乳酸的结晶速率和结晶度。当PPZn的质量分数为5％0时TCs（起始结晶温度）降低了约24℃,TCe（终止结晶温度）降低了约29℃。PPZn的加入使聚乳酸的半结晶时间大大缩短。当PPZn的质量分数为2％时,结晶速率常数增大约5个数量级。     

PLA成核剂的研究进展

综述了PLA不同种类成核剂的研究和应用进展,评价了不同成核剂的成核效果,并且对PLA成核剂的今后发展方向进行了展望。     

The synthesis of poly (lactic acid)-fulvic acid graft polymer and its effect on the crystallization and performance of poly (lactic acid)

ABSTRACT

The poly (lactic acid)-fulvic acid graft polymer (PLA-FA) was synthesized with lactic acid and fulvic acid (FA). The optimum parameters were determined by orthogonal experiment. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy exhibited that FA was successfully grafted onto PLA. Then, PLA/PLA-FA composites were prepared with PLA-FA as fillers by melt blending. The structure characterization and performance tests demonstrated that PLA-FA effectively enhanced the comprehensive performance of PLA composites. The rheological analysis demonstrated that PLA-FA had plasticization effect. The non-isothermal crystallization kinetics demonstrated that PLA-FA promoted the crystallization rate of PLA composites, improving toughness of PLA composites.     

Nucleating agent for poly(L‐lactic acid)—An optimization of chemical structure of hydrazide compound for advanced nucleation ability

A series of compounds having hydrazide groups was prepared and evaluated as nucleating agent for poly(L ‐lactic acid) by differential scanning calorimetry. Hydrazide compounds derived from benzoic acid, 2‐hydroxybenzoic acid, 3‐tert‐butylbenzoic acid, and 2‐aminobenzoic acid, where two of hydrazide compounds connected by four methylene chain were evaluated in series. Benzoylhydrazide type was found to be more effective on the enhancement of crystallization of poly(L ‐lactic acid). Effects of connecting length of methylene chain numbers between two of benzoylhydrazide on the nucleation ability were also evaluated. Benzoylhydrazide‐type compound having 10 methylenes, that is, decamethylenedicarboxylic dibenzoylhydrazide demonstrated excellent nucleation ability, and the resulted crystallization temperature and enthalpy of PLA with the compound of 1 wt % loading were 131°C and 46 J g^?1. The achieved crystallization temperature and enthalpy were over 10°C and over 10 J g^?1 higher than PLA with conventional nucleating agents, such as talc and ethylenebis (12‐hydroxystearylamide). Thus, the improvement in processability, productivity, and heat resistance of PLA is suggested to be achieved by using decamethylenedicarboxylic dibenzoylhydrazide as a nucleating agent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 198–203, 2007     

聚乳酸成核剂的研究进展

回顾并展望了聚乳酸成核剂的研究与开发进展,比较和评价了不同类型成核剂对聚乳酸结晶行为的影响,在此基础上提出了开发聚乳酸专用成核剂的思考和建议。     

Enhancing the durability of poly(lactic acid) composites by nucleated modification

Biodegradable poly(lactic acid) (PLA) composites were prepared using an innovative combination of wood fiber (WF) and 1,3,2,4‐bis(3,4‐dimethylobenzylideno)sorbitol (DMDBS). DMDBS acted as an effective nucleating agent, which improved the mechanical properties and slowed down the degradation of the WF/PLA composites. The enzymatic degradation of the composites was examined by immersing in proteinase K or cellulase buffer. The presence of DMDBS resulted in a 26.7% increase of the crystallinity compared to the WF/PLA composites. The increase in crystallinity enhanced the thermal stability and tensile strength of the WF/DMDBS/PLA composites by 8.5%. The durability of the WF/DMDBS/PLA composites after nucleated modification was enhanced after enzymolysis. After nucleated modification, the surface of the WF/PLA composites showed clear cracks due to degradation, while these appeared about 2 weeks later in the case of the WF/DMDBS/PLA composites. The results revealed that the introduction of cellulase degraded WF in the composites, which increased hydrolysis or enzymolysis sites. The combination of nucleated modification and enzyme buffer gave an expanded downstream application of WF/PLA composites in packaging and agricultural materials. © 2019 Society of Chemical Industry     

New insight into the mechanism of enhanced crystallization of PLA in PLLA/PDLA mixture

Poly(lactic acid) (PLA) is a bio‐based and compostable polymer that has quickly developed into a competitive material, but the control of crystallinity is a bottleneck in extended utilization. The crystallization of PLA has been a rich topic because of the existence of two enantiomeric forms of poly(L‐lactic acid) (PLLA) and poly(d ‐lactic acid) (PDLA) can form stereocomplex (SC) crystal with high melting point that can be used to control the crystallization behaviors. The SC crystal was regarded as an effective nucleating agent for promoting the crystallization rate and crystallinity of PLA. We investigated cold crystallization of PLLA/PDLA (1:1) mixture with in situ WAXS measurements and found that the homo‐crystal of PLA formed earlier than the SC‐crystal in the mixture within the measured temperature range, which is different from the melting crystallization. The final crystalline structures are in correspondence with the melting and cold crystallization temperature, and the transition of homo‐PLA (δ to α) is not altered by the crystallization procedure. The SC‐crystal can be detected in both cold and melting crystallization of the mixture at the temperatures lower than 150 °C, which is conflict with the reported results. A new crystallization mechanism of the mixture was proposed to understand the crystallization behaviors in PLLA/PDLA mixtures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45663.     

聚乳酸有机成核剂研究进展

聚乳酸作为生物可降解材料应用广泛,但是结晶速率非常慢,添加成核剂可以改善其结晶速率,其中有机成核剂因其与聚乳酸良好的相容性备受关注。本文重点综述了有机成核剂的种类及其对聚乳酸结晶性能的改善情况,并展望了有机成核剂今后的发展方向。     

Effect of sepiolite on the crystallization behavior of biodegradable poly(lactic acid) as an efficient nucleating agent

To enhance the crystallization kinetics of poly(lactic acid) (PLA), fibrous sepiolite was explored for nucleating the crystallization of PLA. PLA/sepiolite nanocomposites were prepared via the melt‐extrusion method. The effect of sepiolite on the crystallization behavior, spherulite growth and crystal structure of PLA were investigated by means of differential scanning calorimetry (DSC), polarized optical microscope (POM), wide angle X‐ray diffraction (WAXD), Fourier transform infrared (FTIR), and scanning election microscope (SEM). On the basis of DSC and POM results, the overall crystallization kinetics of PLA/sepiolite nanocomposites were significantly enhanced leading to higher crystallinity and nucleation density, faster spherulite growth rate (G) and lower crystallization half‐time (t_1/2) compared with the neat PLA. Under non‐isothermal conditions, the PLA blend comprising 1.0 wt% of sepiolite still revealed two crystallization peaks upon cooling at a rate of 35°C/min. Above phenomena strongly suggested that sepiolite was an effective nucleating agent for PLA. FTIR and WAXD analyses confirmed that the crystal structure of PLA matrix was the most common α‐form. SEM micrographics illustrated the fine three‐dimensional spherulite structures with the lath‐shape lamellae regularly arranged in radial directions. POLYM. ENG. SCI., 55:1104–1112, 2015. © 2014 Society of Plastics Engineers