Toughening of polylactic acid using styrene ethylene butylene styrene: Mechanical,thermal, and morphological studies

Polylactic acid, PLA, derived from renewable resources has gained great attention nowadays owing to their sustainability, biodegradability, superior property, and transparency. However, intrinsic brittleness and low toughness severely limits its variety of applications. Blending of PLA with other polymers is more economical and more flexible technique for the property improvement of PLA. In this study, Styrene Ethylene Butylene Styrene (SEBS) and Maleic Anhydride grafted SEBS (MA‐g‐SEBS) are used as toughening agents to study their effect for its toughness, high strength and heat resistance on PLA. PLA/SEBS and PLA/Maleic Anhydride grafted SEBS blends were prepared under four different compositions by melt mixing technique using a corotating twin–screw extruder after optimizing the mixing conditions. The mechanical properties of the blends such as tensile, flexural, and impact strengths were investigated using specimens prepared by injection molding process. The percentage elongation and impact strength of PLA/MA‐g‐SEBS blends were found to be increased significantly by 540 and 135%, respectively in comparison with virgin PLA and PLA/SEBS blends. However, tensile strength and modulus of PLA/SEBS and PLA/MA‐g‐SEBS blends decreased compared with pristine PLA. SEM behaviour supported the higher impact property of PLA with the incorporation of modified SEBS via multiple crazing and cavitation mechanisms. DSC study also supported greater compatibility between maleated SEBS and PLA. POLYM. ENG. SCI., 56:669–675, 2016. © 2016 Society of Plastics Engineers     

Mechanisms of plastic deformation in biodegradable polylactide/poly(1,4‐cis‐isoprene) blends

Polylactide (PLA), a main representative of biodegradable and made from renewable resources polymers, is surprisingly brittle at ambient temperature. In this article it is investigated how to increase its toughness by a strategy called “rubber toughening” using poly(1,4‐cis‐isoprene), a major component of natural rubber, which is immiscible with PLA, could be well dispersed in PLA matrix and is biodegradable. Immiscible blends of PLA with poly(1,4‐cis‐isoprene) were prepared by melt blending and their properties were studied and optimized. Incorporation of as low as 5 wt % of rubber increased the strain at break of compression molded film during uniaxial drawing, and also improved its tensile impact strength by 80%. The complex mechanism of plastic deformation in the blends leading to improvement of ductility and toughness was revealed. The rubbery particles initiated crazing at the early stages of deformation, as evidenced by transmission and scanning electron microscopy and also by small angle X‐ray scattering. Crazing was immediately followed by cavitation inside rubber particles, which further promoted shear yielding of PLA. The sequence of those mechanisms was proven by microscopic investigation. All three elementary mechanisms acting in the sequence indicated are responsible for surprisingly efficient toughening of PLA by a major component of natural rubber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

原位反应增容制备可生物降解PLA/PCL复合材料

基于原位反应增容原理制备了一种可生物降解的聚乳酸(PLA)/聚己内酯(PCL)共混材料。探究了PLA/PCL不同配比及相容剂乙烯-丙烯酸丁酯-甲基丙烯酸缩水甘油酯(EBA-GMA)(8份)对增韧效果的影响,目的是研究设计一种增韧效果最佳的PLA/PCL/EBA-GMA可降解材料。并采用平板流变仪、傅里叶红外光谱仪(FTIR)、扫描电子显微镜(SEM)及差示扫描量热法(DSC)对其反应机理、微观形貌及热性能进行了表征。结果表明,在不加相容剂时,PLA/PCL(80/20)能取得最好的增韧效果;加入8份相容剂后,PLA/PCL(85/15)的缺口冲击强度达75.4 kJ/m^2,增韧效果最好。     

Effect of interface on elastic and toughening behavior in poly lactic acid/thermoplastic starch blends: Micromechanical finite element analysis

It is frequently emphasized that the action of interfacial adhesion is a critical parameter to improve the stiffness and toughness of polylactic acid/thermoplastic starch (PLA/TS) blends. In this work, the micromechanical behavior of PLA/TS blends with droplet morphology selected from literature is predicted and analyzed systematically by finite element analysis. A quantitative assessment of the effect of interface (perfect or imperfect) on the elastic behavior and craze initiation for toughening of PLA/TS blends is presented. For the elastic behavior, the PLA phase is the blend's load-bearing component as the TS is more compliant than PLA, so an interface perfectly bonded reduces the blend's elastic modulus when compared to the modulus obtained if the interface is weakly bonded. Regarding the toughening behavior, as a compliant phase, the TS has the potential to nucleate stable crazes in the host PLA matrix independently of the degree of interfacial adhesion because the highly stressed region lies near the equator of the particle; nonetheless, the critical stress for craze initiation is very sensitive to the TS particle size. On the other hand, as the TS is less capable than PLA to develop large hydrostatic stresses, the TS has a low potential to dissipate energy by cavitation.     

聚乳酸/尼龙11/氯醚弹性体三元共混体系结构与性能研究

以生物基尼龙11(PA11)和氯醚橡胶(ECO)作为聚乳酸(PLA)的增韧和耐热改性剂,通过熔融共混的方法制备了PLA/PA11/ECO三元共混体系,并系统表征了体系的相容性、形貌结构、热行为及物理性能.PA11的存在改善了共混体系组分之间相容性.连续相PA11能有效提高PLA基体的维卡软化温度至160 ℃以上.PLA...     

Thermal,mechanical, and morphological properties of polylactic acid toughened with an impact modifier

Polylactic acid (PLA) was melt‐blended with different amount (0 to 50 wt %) of a commercially available ethylene acrylate copolymer impact modifier. PLA/impact modifier blends were prepared via an internal mixer and compression molded into test specimens. The thermal, mechanical, and morphological properties of the blends were investigated. The addition of impact modifier decreased the ability of PLA to crystallize and/or recrystallize. The degree of crystallinity of PLA decreased while the cold crystallization temperature shifted to higher temperatures with increasing the impact modifier content. PLA/impact modifier blends were partially miscible. This was confirmed by the dynamic mechanical analysis (DMA) tests. With increasing the impact modifier content, the blends showed some improvement in the elongation at break and notched impact strength indicating the toughening effects of the impact modifier. In contrast, the yield stress and tensile modulus decreased with the increase in the impact modifier content. Scanning electron microscopy (SEM) micrographs revealed that the toughening mechanisms among others involved shear yielding or plastic deformation of the PLA matrix induced by interfacial debonding between the PLA and the impact modifier domains. PLA with 30 wt % impact modifier showed comparable yield stress and tensile modulus and better elongation at break and impact strength (+90%) than those of polypropylene (PP). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123:2715–2725, 2012     

PLA/POE-g-GMA共混物的制备及性能研究

采用熔融反应法制备乙烯-辛烯共聚物（POE）接枝甲基丙烯酸缩水甘油酯（GMA）（POE-g-GMA）,实现POE反应的官能化,通过反应共混的方法制备聚乳酸（PLA）/POE共混物,考察了POE和POE-g-GMA对PLA的力学性能和热性能及微观形态的影响。结果表明：POE-g-GMA要有适当的接枝率,增韧效果才显著,用0.6%～0.8%接枝率的POE-g-GMA增韧PLA,当POE-g-GMA质量分数达到20%时,共混物的缺口冲击强度提高到基体PLA的6倍左右;同时材料的热性能基本不受影响。POE与PLA间相容性不好,接枝后与PLA间相容性得到改善。     

An overview of toughening polylactic acid by an elastomer

Due to environmental concern and depletion of fossil fuel, research on biopolymer is gaining interest among researchers. Polylactic acid (PLA) is produced from renewable resources. PLA has high tensile strength and high modulus, and it can be processed by using conventional processing methods. However, some properties of PLA limit the usage, such as brittleness, low impact resistance, low thermal stability, and high cost. Overall, the toughening approach of PLA, blending with elastomer has been one of the main focuses. This review paper is intended to provide general information regarding progress made in PLA toughening by an elastomer.     

PPC与IPDI原位聚合增韧聚乳酸

以聚碳酸亚丙酯多元醇(PPC)和异佛尔酮二异氰酸酯(IPDI)为反应性增韧单体,在熔融共混过程中原位聚合生成聚氨酯(PU)增韧相,制备了新型增韧PLA/PU材料。通过FTIR、万能电子试验机、TG、DSC、SEM测试研究了单体用量对PLA共混物加工性、相容性及韧性的影响规律。结果表明:随着增韧单体用量的增加,共混物中PLA组分的冷结晶温度(Tc)和玻璃化转变温度(Tg)降低;当n(NCO)/n(OH)=1/1,PPC用量为30%时,共混物的断裂伸长率和冲击强度比纯PLA分别增加71.8倍和15.6倍;原位聚合物对PLA有较好的增韧效果。     

PLA/PC复合材料的增韧改性研究

采用相容剂乙烯-丙烯酸丁酯(E-BA)和乙烯-丙烯酸甲酯-甲基丙烯酸缩水甘油酯(E-MA-GMA)对聚乳酸/聚碳酸酯(PLA/PC)复合材料进行增韧改性。同时将相容剂E-MA-GMA和E-BA复配,进一步对PLA/PC复合材料进行增韧。结果表明:4%的E-BA和6%的E-MA-GMA使复合材料的冲击强度提高了9¹0倍;E-MA-GMA和E-BA的比例为4:2时,复合材料的冲击强度达到990 J/m。     

Morphology and properties of the biosourced poly(lactic acid)/poly(ethylene oxide‐b‐amide‐12) blends

Biosourced poly(lactic acid) (PLA) blends with different content of poly(ethylene oxide‐b‐amide‐12) (PEBA) were prepared by melt compounding. The miscibility, phase structure, crystallization behavior, mechanical properties, and toughening mechanism were investigated. The blend was an immiscible system with the PEBA domains evenly dispersed in the PLA matrix. The PEBA component suppressed the nonisothermal melt crystallization of PLA. With the addition of PEBA, marked improvement in toughness of PLA was achieved. The maximum for elongation at break and impact strength of the blend reached the level of 346% and 60.5 kJ/m², respectively. The phase morphology evolution in the PLA/PEBA blends after tensile and impact tests was investigated, and the corresponding toughening mechanism was discussed. It was found that the PLA matrix demonstrates obvious shear yielding in the blend during the tensile and impact tests, which induced energy dissipation and therefore lead to improvement in toughness of the PLA/PEBA blends. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

原位反应法制备聚乳酸/聚氨酯共混物及性能

以聚乳酸（PLA）、聚四氢呋喃醚二醇（PTMG）和液化4,4′-二苯基甲烷二异氰酸酯（L-MDI）为原料,通过原位反应法制备了PLA/聚氨酯（PU）共混物,研究了PLA/PU共混物的反应原理、力学性能、断面形貌、动态流变性能以及结晶性能。结果表明,在原位反应中有微交联结构PU生成,且伴随着PLA的扩链和枝化反应;PLA/PU共混物的韧性得到显著提高,当PU含量为30 %（质量分数,下同）时,共混物的断裂伸长率、断裂韧性和缺口冲击强度分别达到230 %、134.13 MJ/m3和34.19 kJ/m2,较纯PLA分别增加了16.6、8.1和11.1倍,此时拉伸强度仍保持在较高水平（49.7 MPa）;纯PLA和PLA/PU共混物熔体均为假塑性流体,共混物具有更高的储能模量和复数黏度;PLA/PU共混物比纯PLA的结晶速率高,晶体完善程度高。     

胺端基型超支化乙二胺三嗪聚合物对PLA/PPC的增韧改性研究

以乙二胺和三聚氯氰作为原料,以丙酮为溶剂,通过“一步法”合成了胺端基型的超支化乙二胺三嗪聚合物(HBETP)。以HBETP作为改性剂,采用双螺杆挤出机熔融共混和注射成型法制备了聚乳酸(PLA)/聚碳酸亚丙酯(PPC)共混物,并用差示扫描量热仪(DSC)、 热失重分析仪(TGA)、电子万能试验机、扫描电字显微镜(SEM)等测试手段对共混物的热性能、力学性能以及断面形貌等进行表征与测试。结果表明,与PLA/PPC共混物相比,当HBETP含量为0.6份时,PLA/PPC/HBETP共混体系在保持拉伸强度基本不变的基础上,断裂伸长率和冲击强度分别提高了266.0 %和122.9 %;HBETP是一种增韧PLA/PPC共混物的有效助剂。     

Mechanical,rheological, and crystallinity properties of polylactic acid/polyethylene glycol-polydimethylsiloxane copolymer blends by melt blending

Polylactic acid (PLA) is high in strength and modulus, but its applications are limited partly due to its inherent brittleness. It is difficult to keep the toughness and transparency of modified PLA without damaging its tensile strength and crystallinity. To improve the properties of PLA, polyethylene glycol-polydimethylsiloxane copolymer (PEG-PDMS) was incorporated to PLA via melt blending. By incorporating only 5 wt% of PEG-PDMS into PLA matrix, the elongation at break of the blends increased from 6% to 58% and the tensile strength was found to be 48.8 MPa. Differential scanning calorimetry demonstrated that the crystallinity of PLA/5%PEG-PDMS blends reached 33.5%. At the same time, the energy storage modulus (G) and complex viscosity (η*) of the blends had been improved. UV–vis test showed the light transmittance of the PLA/5%PEG-PDMS blends was slightly decreased. The toughened materials are sufficient to cope with the challenges brought by complex environments, achieving an efficient toughening effect.     

Effects of moisture content and heat treatment on the physical properties of starch and poly(lactic acid) blends

Starch, a hydrophilic renewable polymer, has been used as a filler for environmentally friendly plastics for about 2 decades. Starch granules become swollen and gelatinized when water is added or when they are heated, and water is often used as a plasticizer to obtain desirable product properties. The objective of this research was to characterize blends from starch and poly(lactic acid) (PLA) in the presence of various water contents. The effects of processing procedures on the properties of the blends were also studied. Blends were prepared with a lab‐scale twin‐screw extruder, and tensile bars for mechanical testing were prepared with both compression and injection molding. Thermal and mechanical properties of the blends were analyzed, and the morphology and water absorption of the blends were evaluated. The initial moisture content (MC) of the starch had no significant effects on its mechanical properties but had a significant effect on the water absorption of the blends. The thermal and crystallization properties of PLA in the blend were not affected by MC. The blends prepared by compression molding had higher crystallinities than those prepared by injection molding. However, the blends prepared by injection molding had higher tensile strengths and elongations and lower water absorption values than those made by compression molding. The crystallinities of the blends increased greatly with annealing treatment at the PLA second crystallization temperature (155°C). The decomposition of PLA indicated that PLA was slightly degraded in the presence of water under the processing temperatures used. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3069–3082, 2001     

Assessment of miscibility,crystallization behaviors,and toughening mechanism of polylactide/acrylate copolymer blends

In this study, acrylate (ACR) copolymer was used to toughen polylactide (PLA). Dynamic mechanical analysis and differential scanning calorimetry results showed that PLA was partially miscible with ACR. Isothermal crystalline behavior indicated that the incorporation of ACR significantly prevented the crystallization of PLA. The transmission electron micrograph showed that ACR was uniformly dispersed in PLA matrix. The mechanical properties of PLA could be improved by the addition of ACR. The analysis of yield stress indicated mild interfacial adhesion between PLA and ACR. Scanning electron micrograph of PLA/ACR blends revealed that the major toughening mechanism was matrix shear yield and plastic flow. Complex viscosity values of PLA/ACR blends were remarkably improved with the incorporation of ACR. Moreover, the van Gurp–Palmen plot, the rheological percolation threshold for the blends was lower than 15 wt%. The incorporation of ACR decreased the absorption coefficient (α), which was caused decreasing transmittance of PLA. POLYM. ENG. SCI., 55:386–396, 2015. © 2014 Society of Plastics Engineers     

Influence of the morphology and viscoelasticity on the thermomechanical properties of poly(lactic acid)/thermoplastic polyurethane blends compatibilized with ethylene-ester copolymer

Viscoelastic, interfacial properties, and morphological data were employed to predict the thermal and mechanical properties of compatibilized poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) blends. The combination of interfacial thickness measured by contact angle and entanglement density determined by dynamical mechanical analysis analyze data was employed to evaluate the mechanical behavior of PLA/TPU blends with and without ethylene-butyl acrylate-glycidyl methacrylate (EBG) compatibilization agent. The PLA/TPU blend (70/30 wt %) was prepared in a Haake internal mixer at 190 °C and compatibilized with different contents of EBG. The evaluation of the interfacial properties revealed an increase in the interfacial layer thickness of the PLA/TPU blend with EBG. The scanning electronic microscopy images showed a drastic reduction in the size of the dispersed phase by increasing the compatibilizer agent EBG content in the blend. The compatibilization of the PLA/TPU blends improved both the Izod impact strength and yield stress by 38 and 33%, respectively, in comparison with neat PLA/TPU blend. The addition of EBG into PLA/TPU blends significantly increased the entanglement density and the PLA toughening but resulted in a decrease of PLA deformation at break. The PLA and TPU glass transitions were affected by the EBG, suggesting that the PLA and TPU domains were partially miscible. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48926.     

Toughening polylactide with epoxidized styrene–butadiene impact resin: Mechanical,morphological, and rheological characterization

Styrene–butadiene impact resin (SBC) was chosen as the toughening agent to improve the tensile toughness of polylactide (PLA). Epoxidized SBC (ESBC) with different epoxidation degree were prepared by epoxidation using in situ peroxoformic acid method and a series of PLA/SBC(ESBC) blends were prepared by melt blending. The elongation at break of the PLA/ESBC blends was greatly improved, which was reflected in the slight decrease in the tensile strength and tensile modulus. Moreover, the tensile strength and tensile modulus were not significantly affected by the epoxidation degree of ESBC. For example, the incorporation of ESBC28.8% (30 wt %) to PLA caused an obvious increment of elongation at break from 3.5% of pure PLA to 305.0%, while the tensile modulus and tensile strength decreased to 80 and 78% of pure PLA, respectively. Scanning electron microscopy observations of cryo‐fractured surface morphology and particle size analysis demonstrated that the compatibility of the PLA/ESBC blends was improved significantly compared to PLA/SBC blend. PLA/ESBC(70/30) blends exhibited shear‐thinning behavior over the range of the studied shear rate. With an increase in shear rate, the non‐Newtonian index of the blends decreased gradually. Furthermore, the flow behavior of PLA/ESBC(70/30) blends was more sensitive to the shear rate than pure PLA. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46058.     

Toughening polylactide with a catalyzed epoxy‐acid interfacial reaction

Polylactide (PLA) is a promising material, with favorable modulus, renewable sources, and biodegradability. However, its low extension at break (4–7%) and toughness (notched Izod, 26 J/m) limit its applications (Anderson et al., Polym. Rev., 48, 85 (2008)). PLA toughening has been the subject of recent reviews, and is the basis for several commercial products. This work aims to increase PLA toughness using rubbery, linear low‐density polyethylene (LLDPE), glycidyl methacrylate functional PE compatibilizer (EGMA), and novel catalysts that promote copolymer formation at the interface of immiscible blends of PLA and EGMA/LLDPE. Droplet size was reduced from 2.7 µm to 1.7 µm with addition of 5 wt% EGMA, and further to 1.0 µm with the addition of cobalt octoate catalyst. Extension at break of 200% is achieved with only 5 wt% EGMA, 15 wt% LLDPE, and 0.01 M cobalt octoate, leading to an increase in tensile toughness of over an order of magnitude (compared to neat PLA). This work demonstrates that catalysts can reduce the amount of reactive compatibilizer necessary to achieve a given PLA toughness. POLYM. ENG. SCI., 58:28–36, 2018. © 2017 Society of Plastics Engineers     

Properties of poly(lactic acid) blends with various starches as affected by physical aging

Poly(lactic acid) (PLA) and starch are both biodegradable and renewable polymers derived from agricultural feedstock. A previous study showed that a small amount (0.5%) of methylenediphenyl diisocyanate (MDI) could enhance the mechanical properties of starch and PLA blends by improving the interfacial interaction. In this study, blends of PLA (1/1, w/w) and starch with or without MDI were evaluated for thermal and mechanical properties as well as morphology, as affected by physical aging when stored up to 12 months at 25 °C and 50% relative humidity. The blends were prepared by thermally blending PLA with wheat starch, corn starch, and/or high amylose corn starch, with or without MDI. All samples exhibited phenomena of physical aging. The samples with MDI aged more slowly, showing a slower reduction rate of excess enthalpy relaxation, than those without MDI. The mechanical properties decreased slowly as aging proceeded. Microstructure showed a reduced interaction between starch and PLA around the interface with aging. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3683–3689, 2003