Crystallization behavior of poly(lactide)/poly(β‐hydroxybutyrate)/talc composites

The morphology and miscibility of commercial poly(lactide) (PLA)/poly(β‐hydroxybutyrate) (PHB, from 5 to 20 wt %) blends prepared by melt extrusion method, were investigated using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) observations. The results show that for all the studied blend contents, PLA/PHB blends are immiscible. The effects of PHB and talc on the nonisothermal cold crystallization kinetics of PLA were examined using a differential scanning calorimetry (DSC) at different heating rates. PHB acted as a nucleating agent on PLA and the addition of talc to the blend yielded further improvement, since significant increase in the enthalpy peak was observed for samples containing 10 wt % PHB and talc (from 0.5 to 5 phr). The crystallization kinetics were then examined using the Avrami–Jeziorny and Liu–Mo approach. The simultaneous presence of PHB and talc induced a decrease of the crystallization half time. The evolution of activation energies determined with Kissinger's equation suggests that blending with PHB and incorporating talc promote nonisothermal cold crystallization of PLA. The synergistic nucleating effect of PHB and talc was also observed on isothermal crystallization of PLA from the melt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

Nonisothermal crystallization kinetics of poly(lactide)—effect of plasticizers and nucleating agent

Poly(lactide), a bio‐based aliphatic polyester, is a subject to large research effort. One point of optimization is the acceleration of its crystallization kinetics to promote crystallinity under nonisothermal polymer processing conditions by means of compounding with nucleating agents and plasticizers. The nonisothermal crystallization kinetics of neat and formulated poly(L,D ‐lactide) (PDLLA) from the melt with talc and polyethylene glycol (PEG) or acetyl tributyl citrate (ATBC) were studied with the help of the Avrami–Jeziorny and Liu–Mo analysis. Talc showed to be a moderately efficient nucleating agent, as it causes only small increase of crystallization kinetics and shows no effect on the crystallization activation energy. A synergistic effect with plasticizers was observed, expanding the crystallization window significantly. PEG was found to be a more efficient plasticizer than ATBC but causes large decrease in the molecular weight average of PDLLA upon thermal treatment. The talc/ATBC system is efficient starting with an ATBC concentration of 9 wt%. The acceleration observed was a crystallization half‐time decrease of 30% compared to neat PLA and reaching maximum crystallization enthalpies even at cooling rate of 25°C min^?1. The ATBC/talc system can be recommended as an efficient system for acceleration of nonisothermal crystallization kinetics of PDLLA. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Talc reinforcement of polylactide and biodegradable polyester blends via injection-molding and pilot-scale film extrusion

As a renewable and biodegradable polymer, polylactide (PLA) has taken a foothold in the packaging industry. However, the thermomechanical and barrier properties of PLA-based films need to be improved to facilitate a wider adoption. To address this challenge, we examined the effect of talc reinforcement in composites based on PLA and a biodegradable polyester. Masterbatches of the polymers and talc were produced by melt compounding and processed by either injection-molding or film extrusion in a pilot-scale unit operating at 60–80 m/min. The effect of talc was investigated in relation to the morphological, thermal, mechanical, and barrier properties of the composites. Based on SEM-imaging, talc was found to increase the miscibility of PLA and the polyester while acting as a nucleating agent that improved PLA crystallinity. While this effect did not track with an increased mechanical strength, the composites with 3–4 wt% talc displayed a significantly higher barrier to water vapor. Compared to the neat polymer films, a reduction of water vapor transmission rate, by ~34–37%, was observed at 23°C/50% RH. Meanwhile, the systems loaded with 1 wt% talc showed a reduction in oxygen transmission rates, by up to 34%. Our results highlight the challenges and prospects of commercial PLA-based blends filled with talc from films extruded in pilot-scale units.     

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.     

Effect of nucleation and plasticization on the crystallization of poly(lactic acid)

In this paper, different strategies to promote PLA crystallization were investigated with the objective of increasing the crystalline content under typical polymer processing conditions. The effect of heterogeneous nucleation was assessed by adding talc, sodium stearate and calcium lactate as potential nucleating agents. The PLA chain mobility was increased by adding up to 10 wt% acetyl triethyl citrate and polyethylene glycol as plasticizers. The crystallization kinetics were studied using DSC analysis under both isothermal and non-isothermal conditions. The isothermal data showed that talc is highly effective in nucleating the PLA in the 80-120 °C temperature range. In the non-isothermal DSC experiments, the crystallinity developed upon cooling was systematically studied at cooling rates of 10, 20, 40, and 80 °C/min. The non-isothermal data showed that the combination of nucleant and plasticizer is necessary to develop significant crystallinity at high cooling rates. The nucleated and/or plasticized PLA samples were injection molded and the effect of mold temperature on crystallinity was determined. It was possible to mold the PLA formulations using mold temperatures either below 40 °C or greater than 60 °C. At low temperature, the molded parts were nearly amorphous while at high mold temperatures, the PLA formulation with proper nucleation and plasticization was shown to achieve crystallinity levels up to 40%, close to the maximum crystalline content of the material. Tensile mechanical properties and temperature resistance of these amorphous and semi-crystalline materials were examined.     

Physical and mechanical properties of poly(L‐lactic acid) nucleated by dibenzoylhydrazide compound

Benzoylhydrazide compounds were evaluated as a nucleating agent for poly(L ‐lactic acid) (PLA). From the results of the differential scanning calorimetry, octamethylenedicarboxylic dibenzoylhydrazide (OMBH) was found to be most effective for acceleration of PLA crystallization under higher cooling rate of ?50°C min^?1. PLA with OMBH of 1 wt % exhibited very short crystallization half‐time with wide range of isothermal temperature from 90 to 130°C. The molding cycle time of PLA with OMBH in injection molding was less than 3 min, and the cooling time was one‐third of ethylenebis(12‐hydroxystearylamide)/talc system as a nucleating agent. Physical and mechanical properties improved extremely, and the heat distortion temperature of 124°C, flexural modulus of 4.1 GPa, and Izod impact strength of 7.9 kJ m^?2 were achieved. This indicates that the utilization of OMBH makes it possible to extend the application range of PLA as automotive parts and electric appliances, which require higher heat resistance and stiffness. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 244–250, 2007     

Effect of crystallization on barrier properties of formulated polylactide

Polylactide (PLA), a biodegradable polymer obtained from biomass, was formulated with a nucleating agent, talc, and a plasticizer, acetyl tributyl citrate, and cold crystallized in α and α′ form. The barrier properties of crystallized PLA were investigated as a function of the formulation and the crystalline form, thanks to three molecules with increasing polymer interactions, i.e. helium, oxygen and ethyl acetate (EA). Contrary to expectation, the oxygen diffusion coefficient in neat and formulated PLA did not decrease with crystallization. Even an increase of the diffusion coefficient was noticed for the most interacting probe, EA, in formulated PLA. Conditioning of neat and formulated PLA in an atmosphere containing EA vapour caused a modification of the material structure by plasticization and induced crystallization even at small EA activities. The plasticizing effect caused the glass transition temperature T_g to shift to below ambient temperature. In the case of neat PLA induced crystallization in solely the α form was obtained, and in the case of formulated PLA a blend of α and α′ forms was observed. Copyright © 2011 Society of Chemical Industry     

生物质纤维和改性木质素对聚乳酸结晶性能的影响

采用改性木质素(MZS)作为成核剂,生物质纤维(BF)作为增强剂,通过双螺杆挤出机制备了生物降解的聚乳酸(PLA)/BF/MZS材料。采用差式扫量热仪(DSC)、电子万能试验机和扫描电子显微镜(SEM)分析了BF和MZS对PLA材料性能的影响。结果表明,BF和MZS有效提高了PLA的结晶能力和力学性能。当BF和MZS的含量分别为15%和1%时,PLA材料结晶度提高至67.1%,在50℃/min降温速率下仍具有较高的结晶能力。105℃等温结晶时,15%BF和1%MZS的PLA材料半结晶时间降低至9.0 s,比纯PLA缩短了72.2%。当PLA含有3%BF和1%MZS时,拉伸强度和冲击强度分别为70.1 MPa和7.4 kJ/m^2,比纯PLA分别提高了7.8%和10.4%,根据SEM显示,当BF含量为3%时,在PLA材料中分布较均匀。     

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。     

聚甲醛结晶性能的改性

研究了高摩尔质量羧酸盐类成核剂HC对聚甲醛（POM）的结晶成核作用，采用示差扫描量热分析（DSC）、偏光显微镜观察（PLM）及等温结晶动力学分析等方法研究了该类成核剂对POM结晶形态、结晶度、结晶速率等的影响，并考察了其力学性能。结果表明，高摩尔质量羧酸盐类成核剂HC的加入，使POM晶粒细化，结晶诱导期缩短，显著提高了POM的结晶速率。     

基于六氢邻苯二甲酸盐的α/β复合成核剂对聚丙烯性能的影响

将α成核剂六氢邻苯二甲酸钙和β成核剂六氢邻苯二甲酸锌复合得到α/β复合成核剂体系,研究了其对等规聚丙烯（iPP）力学性能和结晶性能的影响,并用Avrami理论研究了成核iPP的等温结晶动力学。结果表明,α/β复合成核剂以特定比例复合可以同时提高iPP的刚性和韧性,其中在复合比例为7∶3时,拉伸强度提升了6.7 %,弯曲模量提升了21.8 %,冲击强度提升了108.2 %。进一步研究了复合成核剂在iPP中的浓度效应,随着总添加量的增加,iPP的结晶温度逐渐增加,力学性能趋于稳定,在添加量达到0.4 %（质量分数,下同）时基本不变,此时冲击强度提升了175.3 %,弯曲模量提升了15.0 %,拉伸强度提升了6.5 %。等温结晶动力学的结果表明,复合成核剂体系的加入可以明显缩短iPP的结晶时间并且降低结晶所需的表面能。     

Thermal,morphological, and mechanical properties of biobased and biodegradable blends of poly(lactic acid) and chemically modified thermoplastic starch

In this study, poly(lactic acid) (PLA) was blended with chemically modified thermoplastic starch (CMPS) in a twin‐screw extruder. The characteristic properties of PLA/CMPS blends were investigated by observing the morphology, thermal, and mechanical properties, and biodegradability. Differential scanning calorimetry showed that the PLA/CMPS were thermodynamically immiscible. However, scanning electron microscopy and Fourier transform infrared studies revealed that the interfacial adhesion was improved by the PLA‐g‐starch copolymers that were formed at the interface through a transesterification reaction between PLA and CMPS. The crystallinity of the PLA component in the blend was increased by the addition of the CMPS and was highly affected by the morphology of the blend. The tensile strength and elongation were found to decrease in a linear trend with increasing CMPS content. The biodegradability of the blends increased with increasing CMPS content, while initial time lag decreased. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

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     

Improving mechanical performance of injection molded PLA by controlling crystallinity

Currently, use of poly(lactic acid) (PLA) for injection molded articles is limited for commercial applications because PLA has a slow crystallization rate when compared with many other thermoplastics as well as standard injection molding cycle times. The overall crystallization rate and final crystallinity of PLA were controlled by the addition of physical nucleating agents as well as optimization of injection molding processing conditions. Talc and ethylene bis‐stearamide (EBS) nucleating agents both showed dramatic increases in crystallization rate and final crystalline content as indicated by isothermal and nonisothermal crystallization measurements. Isothermal crystallization half‐times were found to decrease nearly 65‐fold by the addition of only 2% talc. Process changes also had a significant effect on the final crystallinity of molded neat PLA, which was shown to increase from 5 to 42%. The combination of nucleating agents and process optimization not only resulted in an increase in final injection molded crystallinity level, but also allowed for a decreased processing time. An increase of over 30°C in the heat distortion temperature and improved strength and modulus by upwards of 25% were achieved through these material and process changes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

取代芳基磷酸金属盐类成核剂对聚乳酸结晶的影响

通过示差扫描量热仪（DSC）和偏光显微镜（POM）考察了取代芳基磷酸金属盐类成核剂对聚乳酸结晶行为的影响。结果表明：取代芳基磷酸一价盐和三价盐可以较好的改善聚乳酸的结晶，其中取代芳基磷酸锂盐的效果最好，使结晶温度提高了4℃。取代芳基磷酸二价盐对于聚乳酸结晶的改善并不明显。对取代芳基磷酸金属盐类成核剂浓度效应的研究发现：1％为其在聚乳酸中的饱和添加浓度。针对滑石粉和取代芳基磷酸锂盐进行了复配研究，发现复配后的成核剂可以更好的促进聚乳酸的结晶。     

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.     

Structure,Performance and Crystallization Behavior of Poly (Lactic Acid)/Humic Acid Amide Composites

Humic acid amide (HA-amide) was prepared by amidation of HA and dodecylamine (DDA) with carbonyl diimidazole (CDI) as coupling reagent. Furthermore, HA-amide was added to poly (lactic acid) (PLA) as a nucleating agent to prepare poly (lactic acid)/humic acid amide composites (PLA/HA-amide) by melt blending. The structure and performance of PLA/HA-amide composites were investigated by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and rheological analysis. Non-isothermal crystallization kinetics showed the HA-amide enhanced the crystallization rate of PLA. The results of crystallization behavior of PLA/HA-amide composites showed that HA-amide was an efficient nucleating agent of PLA.     

Plasticized and unplasticized PLA/organoclay nanocomposites: Short‐ and long‐term thermal properties,morphology, and nonisothermal crystallization behavior

The short‐ and long‐term thermal properties, organoclay dispersion state, and the nonisothermal crystallization kinetics of organoclay based nanocomposites of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) plasticized PLA were investigated. Differential scanning calorimetry analyses showed that plasticization of PLA/PEG blend was diminished due to physical aging by the time. The change in thermal properties such as glass transition temperature, cold crystallization temperature, and melting temperature was monitored. It was revealed from X‐ray diffraction analyses that in long term, the exfoliated and/or intercalated organoclay structure of nanocomposites observed in short term (just after processing) was differentiated to a tactoidal form (i.e., nonseparated clays). The nonisothermal crystallization behavior and kinetics were examined by using Avrami, Ozawa, and combined Avrami–Ozawa models. Moreover, the nucleating effect of clays was investigated in terms of Gutzow and Dobrewa approaches. It was found out that clays did not act as nucleating agents in plasticized PLA nanocomposites, which was also in good agreement with activation energy values obtained from Kissinger and Takhor models. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012