The crystallization behavior and mechanical properties of polylactic acid in the presence of a crystal nucleating agent

The crystallization behavior of polylactic acid (PLA) was studied in the presence of a crystal nucleating agent, ethylenebishydroxystearamide (EBH). The crystallization rate and crystallinity were significantly increased with addition of EBH. The isothermal crystallization half-time at 105°C was decreased from 18.8 minutes for neat PLA to 2.8 minutes for PLA with 1.0 wt % of EBH. The crystallinity of PLA with 1.0 wt % EBH was about 35% after 5-minute annealing at 105°C. Like neat PLA, the double melting peaks were also observed for nucleated PLA. The changes of the double melt peaks were investigated with various crystallization temperatures, heating rates, and annealing times. The heat deflection temperature (HDT) of nucleated PLA was up to 93°C after annealing. The correlation between crystallinity and HDT was demonstrated. A percolation threshold of crystallinity was found corresponding to HDT. The crystal size of nucleated PLA was significantly decreased with addition of EBH. The mechanical properties of annealed PLA blends simultaneously; showed improved modulus and impact strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

成核剂对聚丙烯力学性能与结晶行为的影响

研究了两种类型的成核剂对国产共聚聚丙烯的结晶形态以及拉伸强度、冲击强度的影响。结果表明:加入TMB-5型成核剂,聚丙烯的冲击强度有一定程度改善,w(TMB-5)为0.1%时,改性聚丙烯的缺口冲击强度达到最大;TMX-2型成核剂可改善聚丙烯的拉伸性能,但抗冲击性能降低较大;TMB-5型成核剂可显著地改变聚丙烯的结晶行为,诱导聚丙烯在结晶过程中主要形成β晶;TMX-2型成核剂可诱导聚丙烯在结晶过程中主要生成α晶,与纯PP相比,α晶的形成能力增强。     

Preparation,dynamic rheological behavior,crystallization, and mechanical properties of inorganic whiskers reinforced polylactic acid/hydroxyapatite nanocomposites

The novel inorganic SiO₂–MgO–CaO whiskers (SMCWs) were incorporated into nano hydroxyapatite (HA) contained polylactic acid (PLA) system to prepare the reinforced PLA/HA/SMCWs nanocomposite. Maleic anhydride grafted PLA (PLA‐g‐MAH) was then used to modify the interface between filler and matrix. The morphology, rheological behavior, crystallization, and mechanical property of the prepared nanocomposites were systematically investigated using scanning electronic microscope, dynamic rheometer, differential scanning calorimeter, polarized light microscope, and mechanical test, respectively. The results showed that the introduced PLA‐g‐MAH obviously improves the filler dispersion and the filler–matrix interfacial compatibility. Interestingly, the incorporated whiskers obviously decrease the complex viscosity and hence could significantly improve the processability of system. However, the introduction of PLA‐g‐MAH increases the complex viscosity to a greater extent. In addition, the added whiskers were found to have complicated influences on the PLA crystallization. On one hand, the incorporated whiskers can enhance the melt crystallization capability of PLA macromolecular chains; on the other hand, the introduced whiskers also show the inhibitive effect on the nucleation of PLA polymer chains and the inhibition degree is related to the loading of whiskers. The combination of whiskers and PLA‐g‐MAH could remarkably improve the mechanical performance of PLA/HA nanocomposite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43381.     

Rheological properties and crystallization behavior of modified polylactic acid using lauroyl peroxide and glycidyl methacrylate

The molecular structure of polylactic acid (PLA) was modified by lauroyl peroxide (LP) as an alkyl free radical and glycidyl methacrylate (GMA) as a reactive co-monomer. We investigated the effect of different preparation methods, that is, the melt and solution, on the structure and physical and mechanical properties of glycidyl methacrylate grafted polylactic acid (PLA-g-GMA). The Fourier transformed infrared spectroscopy (FTIR) was implemented to characterize the final products in order to confirm that GMA was successfully grafted onto PLA. The gel permeation chromatography showed that the molecular weight and polydispersity of the modified PLA were increased by grafting. However, by varying other parameters such as the reaction time and the LP and GMA concentrations, we observed that the resulting products from the melt method are richer in the rheological properties compared with those properties from the solution method. This is due to the different molecular weights resulted from the either preparation methods. From the DSC characteristics of PLA-g-GMA samples, the crystallization degree of the samples prepared from the melt method is greater than that of the solution method. Meanwhile, the cold crystallization for the PLA-g-GMA samples derived from the solution method occurs at higher temperatures compared with the cold crystallization of the samples resulted from the melt method.     

双峰PE生产工艺对其结晶行为和力学性能的影响

采用高温液相凝胶渗透色谱仪、广角X射线衍射仪和拉力机,研究了双峰聚乙烯(PE)生产中环管反应器和气相反应器的工艺参数对双峰PE产品的结晶行为和力学性能的影响。结果表明:环管反应器聚合产物的结晶度随停留时间的延长而减小,气相反应器产物的结晶度随n(H2)/n(C2H4)下降、n(1-C4H8)/n(C2H4)增大和床层分配率增加而减小,双峰PE的拉伸屈服应力和拉伸弹性模量随其结晶度和相对分子质量增加而减小。     

Influence of talc particle size and content on crystallization behavior,mechanical properties and morphology of poly(lactic acid)

This research aimed to employ inorganic filler such as talc to promote crystallization in poly(lactic acid) (PLA). Three different talc particle sizes, namely 1, 5 and 30 µm, were used as nucleating agents; each was compounded with PLA at various contents from 0 to 10 wt%. The crystallization temperature (T _c) reduced most rapidly from 128 to 107 °C with the presence of 1 wt% talc. Beyond this concentration, the T _c still decreased but only minutely. Compared to other sizes, finer talc particles were found to promote a slightly higher degree of crystallinity. X-ray diffraction peaks indicated that the α-crystal was formed in all PLA/talc compositions. The heat distortion temperature values suggested that the modified PLA could resist the thermal deformation from 58 °C to a maximum value of 139 °C when 1 µm talc was added at 10 wt%. With the presence of talc, the composites were more brittle and both tensile elongation at break and impact strength were decreased.     

Influence of process parameters on thermal and mechanical properties of polylactic acid fabricated by fused filament fabrication

Fused filament fabrication is considered one of the most used processes in additive manufacturing rapid prototypes out of polymeric material. Poor strength of the deposited layers is still one of the main critical problems in this process, which affects the mechanical properties of the final parts. To improve the mechanical strength, investigation into various process parameters must be considered. In this article, the influence of different process parameters has been experimentally investigated by means of physicochemical and mechanical characterizations. Special attention was given to the thermal aspect. In that respect, the in situ measurement of temperature profile during deposition indicated that several parameters affect the cooling rate of material and consequently have an influence on the final parts. It was found that the influence of increasing the extruder temperature is more significant in comparison with other process parameters.     

Effect of annealing and orientation on microstructures and mechanical properties of polylactic acid

Two types of polylactic acid (PLA) films (one amorphous and one semi‐crystalline) were produced by sheet extrusion. Talc was used as a nucleation agent for the semi‐crystalline PLA. The films were annealed above their T_g or were uniaxially orientated in two ways: (1) via a drawing system in front of the extruder and die or (2) via a three‐roller stretching system. The slower crystallization rate and lower melting stress of the PLA resulted in amorphous film using the drawing system. Annealing above T_g increased crystallinity and polymer chain relaxation, which resulted in increases in both strength and toughness. Stretching above T_g also produced simultaneous crystallization and chain relaxation, which resulted in increases in both modulus and toughness. Both modulus and tensile strength in the stretching direction were higher than in the crosswise direction. Talc acted not only as a rigid filler to reinforce the PLA, but also as a nucleation agent for the PLA, especially during annealing. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Influence of a synthetic ureido nucleating agent on crystallization behavior and mechanical properties of polyamide 6

A synthetic ureido mixture prepared from the reaction of 4,4′‐diphenylmethane disocynanate (MDI) and cyclohexylamine without using any harmful organic solvents, has been used as a nucleating agent (PNA) for polyamide 6 (PA6). The effect of PNA on the crystallization and mechanical properties of PA6 has been studied by means of differential scanning calorimetry (DSC), polarized optical microscopy (POM), tensile test, melt flow index (MFI), and X‐ray diffraction (XRD). The results show that PNA is an effective nucleation agent for PA6. PNA affects the nucleation mechanism of PA6, and substantially accelerates the crystallization rate of PA6 and gives rise to smaller crystal size. In comparison with PA6, the crystallization temperature (T_c) of PA6/PNA (100/0.5) increases 21.3°C and the degree of sub‐cooling (ΔT_c) decreases 23.7°C. Furthermore, because of the heterogeneous nucleation induced by PNA, the spherulites of PA6 become even and tiny based on POM observation. Polymorph transform has been obtained from XRD analysis. The virgin PA6 is free of γ‐phase crystals, presented as α‐phase crystals in this study, but γ‐phase crystal appears after the introduction of PNA. The mechanical and thermal properties of PA6 are obviously improved by the addition of PNA. POLYM. ENG. SCI., 55:2011–2017, 2015. © 2015 Society of Plastics Engineers     

云母钛珠光颜料的研制

对钛盐的沉析特性、云母精制、颜料制备进行了探讨。研制出云母－钛珠光颜料，即二氧化钛包覆云母，包覆层明显，珠光效果显著。     

高品质BiOCl珠光颜料的制备及其在水性珠光印花涂料中的应用

为突破合成高固含量氯氧化铋 (BiOCl) 晶体时易产生晶体碎片和团聚的瓶颈,本文以聚乙二醇单甲醚-b-聚甲基丙烯酸N,N-二甲基氨基乙酯 (mPEG-b-PDMAEMA) 作分散剂,可控制备了高固含量（高达10 %）、分散性优异的正方形氯氧化铋 (BiOCl) 晶体,以其为珠光颜料,自制的水性聚氨酯 (WPU) 乳液作粘合剂,获得具有不同层次珠光效果的织物珠光印花涂层。分别用光学显微镜、激光粒度仪和 XRD 考察 BiOCl 晶体的形貌、粒径分布和结晶度。并考察珠光印花涂层的透气性、透湿性、水接触角及色牢度等性能。结果表明：BiOCl 晶体的尺寸可控、无碎片和团聚且结晶度高;珠光印花涂层透湿率高于 5500 g/m2?d,透气率在 15～24 mm/s 之间,水接触角高于130 °,耐洗和耐摩擦色牢度达到4级及以上。     

国外云母系珠光颜料研究的新进展

综述了近期国外云母系珠光颜料开发研究的最新进展，分析了多覆层云母珠光颜料能提高遮盖力的原因，阐述了具有高着色能力的有机着色类云母珠光颜料合成研究的现状     

Effect of polyethylene glycol on mechanical properties of bamboo fiber-reinforced polylactic acid composites

The bamboo fiber (BF)-reinforced polylactic acid (PLA) composites were prepared using the twin-screw extruder and injection molding. Thermal gravimetric analyzer results indicated the thermal stability of BF/PLA composites decreased with increasing BF content. Differential scanning calorimeter and X-ray diffraction curves showed that BF played a role as a nucleating agent, but the crystallinity of composite materials decreased with the increasing BF content. The melt flow rate of composites reduced with the increase in BF content, resulting in a poorer processing property. The processability of the composites was improved with the addition of high molecular polyethylene glycol (PEG). Mechanics performance test showed that tensile strength and bending strength of composites increased at low loading with the BF content increased then decreased when the loading continued to increase. The tensile strength of the composite materials reached 65.46 MPa when alkali-treated BF (ABF) content was 20 wt %. The flexural strength of the composites reached 97.94 MPa when ABF content was 10 wt %. Impact performance has also been improved. PEG-20000 was the best plasticizer among the PEG-6000,PEG-10000, and PEG-20000. When the component of PEG was 10 wt %, the elongation increased by 56%. The scanning electron microscopy (SEM) result showed that the fracture of the composites was smooth, most ABF were wrapped in matrix and distribution of ABF in PLA matrix was more uniform. It means that interfacial compatibility of bamboo fiber and PLA improved after BF modified by alkali. High molecular weight PEG enhance melt flow ability of polymer, result in fibers were further enclosed in the PLA matrix and increase properties of composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47709.     

高品质BiOCl珠光颜料的制备及其在水性珠光印花涂料中的应用

为解决合成高固含量氯氧化铋(BiOCl)晶体时易产生晶体碎片和团聚的问题，以聚乙二醇单甲醚-b-聚甲基丙烯酸N,N-二甲基氨基乙酯为分散剂，制备了高固含量(10%)、分散性优异的正方形Bi OCl晶体。以其为珠光颜料，自制的水性聚氨酯(WPU)乳液作黏合剂，制得了具有不同层次珠光效果的织物珠光印花涂层。用光学显微镜、激光粒度仪和XRD考察了BiOCl晶体的形貌、粒径分布和结晶度，并考察了珠光印花涂层的透气性、透湿性、水接触角及色牢度。结果表明，Bi OCl晶体的尺寸可控、无碎片和团聚、结晶度较高；珠光印花涂层透湿率>5500 g/(m²·d)，透气率在15～24 mm/s之间，水接触角>130°，耐洗和耐摩擦色牢度达到4级及以上。     

Effect of processing conditions on crystallization behavior and mechanical properties of poly(lactic acid) staple fibers

Within this study, the applicability of Raman spectroscopy to characterize the crystallinity of PLA staple fibers was evaluated. The influence of the fiber alignment on the possibility to detect crystallinity by using Raman spectroscopy was studied. PLA staple fibers were produced by melt spinning by varying both draw temperature and draw ratio. Systematic interrelationships between the processing parameters of PLA staple fibers and the degrees of crystallinity and the cold crystallization enthalpies were established. Raman spectroscopy showed that the carbonyl stretching band of Raman spectra measured in fiber axis and parallelly polarized was not sensitive to detect crystallinity. However, for perpendicularly polarized measurements, a higher sensitivity was observed. With increasing degree of crystallinity, a reduction of the band width of the normalized carbonyl stretching band was found. The morphology affected the mechanical properties significantly. Increased draw ratio resulted in increased tensile strength and decreased elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42432.     

Influence of equal channel angular pressing on the properties of polylactic acid

The effects of equal channel angular pressing (ECAP) on the microstructures, mechanical, and degradation properties of polylactic acid (PLA) were investigated. The controllable microstructures of PLA can be achieved by a 3D rotary‐die through various combinations of passes and routes (A′ and C′). For A′ route, sample was extruded sequentially through four channels in a plane with compressive or tensile stress alternatively imposed on the two major load bearing surfaces, while for C′ route, sample was extruded only in two vertical channels back and forth with constant compressive or tensile stress imposed on the two major load bearing surfaces. The strong preferential orientation of (200) plane parallelled to the axis direction was formed under the conditions of A′ route for two passes and C′ route for three passes. There was a more uniform distribution in the microhardness for the sample extruded by two passes under C′ route. Meanwhile the sample had higher bending strength after two passes under A′ route, and better facture toughness after three passes under C′ route. The reductions in mass and bending strength of PLA processed by ECAP were more obvious than those of original sample in phosphate‐buffered solution at 37°C for 16 weeks. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers     

Effects of nucleating agents on crystallization behavior and mechanical properties of high-fluid polypropylene

The effects of organic aluminum phosphate (NA-21) and rare earth organic coordination compounds (WBG), serving as ??, ?? nucleating agents, on crystallization and mechanical properties of high-fluid polypropylene (PP) have been investigated. As determined by differential scanning calorimetry, the isothermal crystallization temperature of PP increased from 126.5 to 137.7?°C and 133.6?°C with NA-21 and WBG, respectively. The two endothermal melting peaks of PP blending with WBG indicated the transformation of ??-crystal. The wide-angle X-ray diffraction pattern and melting behavior of PP blending with WBG testified that a high proportion of ??-crystal, which was more than 70%, was induced, while the crystal-phase of PP modified with NA-21 had little change. The mechanical properties of nucleated PP were tested by tensile testing machine and izod pendulum impact tester. A dramatic increment of impact strength, as high as 191%, was obtained for PP with the introduction of WBG, comparing to 132% by NA-21 addition. The impact fracture surfaces were observed by scanning electron microscope; the resistance of crack growth of nucleated PP was better than that of pure PP. Although flexural strength of PP improved in both scenarios, the influence of nucleators on yield strength of PP differed. Yield strength of PP increased by 8.5% when using 0.2?wt% NA-21, but decreased by 6% when using WBG at the same content. Therefore, WBG, a novel ??-nucleator, played an essential role in enhancing impact strength of PP.     

聚乳酸的热降解性能研究

研究了聚乳酸(PLA)在10-40 min和170-200℃的条件下热降解后的特性粘数和端羧基含量的变化。结果表明,在一定温度下,PLA熔体特性粘数随熔融时间的延长而下降,在一定时间下,随熔融温度升高而下降,端羧基含量随熔融温度升高而增大,在PLA成型加工中,应严格控制加工温度。     

Enhancing the mechanical properties of 3D printed polylactic acid using nanocellulose

We report here a systematic investigation of the mechanical properties of polylactic acid (PLA) processed by fused filament fabrication (FFF) 3D printing vs PLA processed by compression molding. Our results show that the tensile strength and modulus of FFF-PLA is 49% and 41% lower, respectively, than compression molded samples of PLA. We also demonstrate here an approach to augment the mechanical properties of 3D printed PLA using nanocellulose. Incorporation of a small quantity (1 wt%) of cellulose nanofibers (CNF) was found to enhance the tensile strength and modulus of 3D printed PLA by 84% and 63%, respectively. X-ray microtomography was used to probe the morphology of 3D printed PLA and PLA/CNF composites. 3D printed PLA/CNF composites had significantly lesser voids as compared to neat 3D printed PLA. Differential scanning calorimetry study revealed that CNF can accelerate the nucleation and crystallization of 3D printed PLA leading to enhanced crystallinity. The thermal stability of 3D printed PLA/CNF composites was not compromised by the addition of CNF. The enhanced mechanical properties of 3D printed PLA/CNF composites can be ascribed to higher crystallinity and lesser defects.     

A monomolecular organophosphate for enhancing the flame retardancy,thermostability and crystallization properties of polylactic acid

Polylactic acid (PLA) is regarded as one of the most promising bioplastics. However, its inherent high flammability of PLA seriously limits its application in the emerging fields. Although the traditional phosphate flame retardants showed excellent flame retardant efficiency in PLA, they often failed to meet the processing requirements of PLA and the thermal stability of PLA composites was decreased after their addition. Herein, an organophosphate flame retardant pentaerythritol bis(phenyl phosphonate) (PBPP) with high thermal stability and phosphorus content was synthesized by the nucleophilic substitution reaction in our laboratory. The introduction of PBPP simultaneously improved the flame retardancy, thermostability and crystallization properties of PLA. Only 3 wt% PBPP endowed PLA composites with UL-94 V-0 grade and higher LOI of 28.3% due to its excellent gas phase effect. Moreover, the crystallinity of PLA/PBPP4 was enhanced from 14.2% of PLA to 32.2% with the improvement of 127%. Because of the similar structure and good compatibility between organophosphate flame retardant and PLA matrix, flame retardant PLA/PBPP maintained almost the same strength as neat PLA. This study provided a novel way for the preparation of a high-performance flame retardant PLA composites with excellent comprehensive properties and it was important to expand the application value of multifunctional PLA materials.