Toughening polylactide by direct blending of cellulose nanocrystals and epoxidized soybean oil

Polylactide (PLA) is a bio-based polymeric material which is earth abundant in nature. It also possesses abundant strength and stiffness making it a promising material for industrial applications. However, its brittle behavior is currently limiting research work on them. As such, an eco-friendly blending approach is developed in this study in order to fabricate a ductile and toughen PLA composites using renewable bio-based materials as a precursor. Specifically, PLA, epoxidized soybean oil (ESO), and frangible powder form of cellulose nanocrystals (CNCs) are melt blended to prepare the ternary composite system (PLA/CNC/ESO). During the composite routing, it is found out that the ESO successfully attached to the surface of CNC which in turn results in CNC/ESO mixtures in the PLA matrix. This intrinsic combination induces cavitation which consumes the energy produced under the stretching and impacting, resulting in the turning of the PLA's brittle phenomenon. In fact, a reasonable increase in the ductility is observed. The elongation and notched impact strength of the ternary nanocomposite are found to be ∼32% and ∼4.8 kJ m⁻², respectively, which are comparatively higher than that of neat PLA or PLA/CNC composites. Differential scanning calorimetry analyses show that the ESO layer on CNC affects the thermal characteristics of PLA in the ternary composite while thermogravimetric analysis shows that there is an increase in the char yield of the composite. Furthermore, scanning electron microscopy analysis shows that the synthesis approach adopted here enables a mechanistically turning of the PLA's brittle phenomenon to ductile. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48221.     

Highly-modified polylactide transparent blends with better heat-resistance,melt strength,toughness and stiffness balance due to the compatibilization and chain extender effects of methacrylate-co-glycidyl methacrylate copolymer

A core-shell modifier with the cross-linked acrylate and silicone copolymer as the core and polymethyl methacrylate (PMMA) as the shell (PASi-g-PMMA) was used to toughen the brittle polylactide (PLA). In addition, the copolymer of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) (MG) was utilized to further enhance the modification efficiency of the PASi-g-PMMA. The MG copolymer played the double roles of compatibilizer and chain extender, which not only improved the interfacial adhesion between the PLA and PASi-g-PMMA particles, but also increased the molecular weight and chain entanglement of the PLA. Compared with the PASi-g-PMMA toughened PLA blend, the PLA/PASi-g-PMMA/MG blends showed much higher heat-resistance, melt strength, transparency, toughness and stiffness balance. When the PASi-g-PMMA content was 20 wt%, 20 wt% MG increased the glass transition temperature (T_g), complex viscosity (η*), transparency, impact and tensile strength of PLA/PASi-g-PMMA blend from 60.1°C, 1.9 × 10³ Pa·s, 76.1%, 748 J/m and 37 MPa to 71.5°C, 0.5 × 10⁴ Pa·s, 78.4%, 860 J/m and 45 MPa for the PLA/PASi-g-PMMA/MG blend. This research provided a facile and practical method to overcome the shortcomings of the PLA and promoted its application in broader fields.     

Toughness enhancement of polylactide with low amounts of poly (butylene adipate-co-terephthalate) through in situ reactive compatibilization

Polylactide (PLA) was melt blended with low amounts of poly (butylene adipate-co-terephthalate) (PBAT) using a simple reactive extrusion process herein, aiming to address the inherent brittleness of PLA without significantly compromising its stiffness. PLA/PBAT (90/10) blends with a small amount of peroxide (0.02 phr) and a second crosslinker agent triallyl isocyanurate (TAIC) were produced to explore the structure-performance relationship evolution in reactive extrusion. The results showed that the PLA blend with an appropriate amount of TAIC (i.e., 0.3 phr) exhibited a remarkable increase in elongation at break, reaching as high as 96%. The sample with high elongation also demonstrated a high stiffness, boasting a Young's modulus of 2.4 GPa and a yield strength of 43 MPa. It was evident that the combination of enhanced compatibility and optimized homogeneous PBAT phase size of approximately 0.6 μm worked synergistically to enhance the toughness of PLA. Conversely, higher TAIC contents resulted in over-crosslinking, despite considerable improvements in compatibility. This study offers a versatile, scalable, and practical method to prepare fully biodegradable PLA blends with high toughness.     

Reinforcement of graphene nanoplatelets on plasticized poly(lactic acid) nanocomposites: Mechanical,thermal, morphology,and antibacterial properties

Plasticized poly(lactic acid) (PLA)‐based nanocomposites filled with graphene nanoplatelets (xGnP) and containing poly(ethylene glycol) (PEG) and epoxidized palm oil (EPO) with ratio 2 : 1 (2P : 1E) as hybrid plasticizer were prepared by melt blending method. The key objective is to take advantage of plasticization to increase the material ductility while preserving valuable stiffness, strength, and toughness via addition of xGnP. The tensile modulus of PLA/2P : 1E/0.1 wt % xGnP was substantially improved (30%) with strength and elasticity maintained, as compared to plasticized PLA. TGA analysis revealed that the xGnP was capable of acting as barrier to reduce thermal diffusion across the plasticized PLA matrix, and thus enhanced thermal stability of the plasticized PLA. Incorporation of xGnP also enhanced antimicrobial activity of nanocomposites toward Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, and Listeria monocytogenes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41652.     

Mechanical and morphological properties of a ternary polyamide 6 nanocomposite with optimized stiffness/toughness performance

While developing new polymers, a high level of stiff and simultaneously tough material behavior is an important goal. This study shows a new approach to optimize the stiffness/toughness behavior of polyamide 6 (PA 6) by incorporating both stiff and elastomeric nanofillers during melt compounding. For stiffness enhancement of PA 6, an organic‐modified layered silicate (organoclay) was used, whereas to compensate for the toughness properties, a nanostructured PA 6/polyether block copolymer (PA 6‐copo) was applied. In the first step, binary nanocomposites have been investigated whereby correlations between morphological and mechanical properties have been derived. Subsequently, these results have been used to adapt the processing conditions for the ternary nanocomposites. Despite a considerable interaction of both nanofillers the stiffness/toughness balance of the PA 6 nanocomposite has been optimized significantly. At a filler content of only 8 mass% organoclay and 8.3 mass% PA 6‐copo, Young's modulus and tensile strength of PA 6 could be increased by 55% and 18%, respectively. In addition, the notched impact strength of PA 6 was enhanced substantially by 58%. POLYM. ENG. SCI., 54:247–254, 2014. © 2013 Society of Plastics Engineers     

Improvement in toughness and crystallization of poly(L‐lactic acid) by melt blending with poly(epichlorohydrin‐co‐ethylene oxide)

Melt blending of poly(lactic acid) (PLA) and poly(epichlorohydrin‐co‐ethylene oxide) copolymers (ECO) was performed to improve the toughness and crystallization of PLA. Thermal and scanning electron microscopy analysis indicated that PLA and ECO were not thermodynamically miscible but compatible to some extent. The addition of a small amount of ECO accelerated the crystallization rate and increased the final crystallinity of PLA in the blends. Significant enhancement in toughness and flexibility of PLA were achieved by the incorporation of the ECO elastomer. When 20 wt% ECO added, the impact strength increased from 5 kJ/m² of neat PLA to 63.9 kJ/m², and the elongation at break increased from 5% to above 160%. The failure mode changed from brittle fracture of neat PLA to ductile fracture of the blend. Rheological measurement showed that the melt elasticity and viscosity of the blend increased with the concentration of ECO. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.     

Compatibilisation of various PLA/thermoplastic elastomer blends with diisocyanate coupling agent

Poly(lactic acid) (PLA) is characterised by its inherent brittleness, a detrimental feature for the production of durable bioplastics. PLA has been toughened by a low amount (12?wt-%) of various thermoplastic elastomers (TPE) including poly(ether-b-ester) (PEEs), poly(ether-b-amide) (PEBA) and poly(ether-b-urethane) (PEU). PLA–TPE blends were prepared by using a twin screw extruder. Ductility and impact resistance can be slightly improved with the incorporation of TPEs but but PEBA appears the most efficient. Reactive compatibilisation has been performed with the addition in the melt of a low amount (2?wt-%) of 4,4-methylene diphenyl diisocyanate. All compatibilised blends exhibit high toughness with similar ductility. These blends preserve good stiffness and high tensile strength. Compatibilised PEBA blends can be considered as super tough poly(lactic acid) materials. This work confirms that the flexibility of the elastomer together with the quality of the interfacial adhesion between the rigid (PLA) and the soft (TPE) phases are the primary factors influencing the toughness.     

Enhancing mechanical and shape memory properties of polylactide/polyamide elastomer blends via reactive blending with a chain extender

The structure and properties of incompatible polylactide (PLA)/polyamide elastomer (PAE) blends were tailored by a chain extender specifically the styrene–glycidyl acrylate copolymer Joncryl ADR4368 (ADR). Various PLA/PAE/ADR blends with different compositions were prepared by melt blending, and their morphology, crystallization behavior, and mechanical and the shape memory properties were systematically investigated. The results showed a uniform dispersion of PAE particles in the PLA matrix for the PLA blends with a reduction in particle size upon the addition of ADR. The crystallization of PLA was retarded, which was confirmed by a decrease in the melt crystallization temperature and an increase in cold crystallization temperature in the PLA/PAE/ADR blends. Rheological analysis showed an improvement in the melt elasticity of the PLA/PAE binary blend due to the presence of ADR, possibly attributed to the formation of long-chain-branched copolymers at the interface. Notably, the PLA/PAE/ADR blend exhibited superior toughness, featuring an elongation at break of 288% and a notched impact strength of 37 kJ·m⁻², along with a high shape memory fixation rate and recovery rate when the ADR content was 1 wt%. Furthermore, the underlying toughening mechanism was elucidated. This work may offer an industrially scalable relevant model to fabricate high-performance PLA materials.     

Toughening biodegradable polylactide with nanopores

The inherent brittleness of biodegradable polylactide (PLA) limits its large-scale applications. A common route for toughening PLA is to incorporate other components by blending. In achieving good toughness, however, other properties such as strength and transparency are usually sacrificed to a large extent. Here we presented a facile approach to toughen PLA with nanopores. By tailoring solution phase separation abundant nanopores with size of about 30 nm was achieved in the PLA films. The presence of nanopores significantly enhanced tensile toughness to about 67 MJ/m³, and good strength and high transparency were retained. Both multiple crazing and shear yielding were contributed to the remarkable toughness improvement. Our approach, advantageous over other routes, opens new opportunities to fabricate tough PLA with a better balance of comprehensive properties.     

聚乳酸基纤维素纳米晶体抗菌包装材料的制备及其性能研究

为改善聚乳酸(PLA)膜的力学性能、阻隔性能和抑菌性能,通过溶液浇铸法制备纤维素纳米晶体(CNC)和槐糖脂(SL)掺杂的PLA复合抗菌膜,探究SL含量(10%)不变时,CNC的含量对PLA/SL/CNC的力学性能、亲疏水性、水蒸气阻隔性和抑菌性能的影响。结果表明:PLA复合膜具有较好的透光性。CNC含量为8%时,CNC与PLA相容性较差。相比纯PLA,PLA/SL/CNC(6%)的拉伸强度高达68.6 MPa,提高93.8%;PLA/SL/CNC(6%)的韧性为36.5×10⁸J/m³,增加46%。PLA/SL/CNC(6%)水接触角为86°,具有疏水性。PLA/SL/CNC(6%)的水蒸气透过系数为2.4(g·cm)/(Pa·s·cm²),与纯PLA相比降低36.8%。PLA/SL/CNC(6%)与利斯特氏菌和金黄色葡萄球菌共培养24h,菌落数分别为0.8 lgCFU/mL和0.4 lgCFU/mL,具有较好的抑菌效果。     

Influences of three different ethylene copolymers on the toughness and other properties of polylactide

The aim of this study was to investigate influences of three different ethylene copolymers on the toughness and other properties of very brittle biopolymer PLA (polylactide). For this aim, PLA was melt blended by twin-screw extruder with various amounts of ethylene vinyl acetate (EVA), ethylene-methyl-acrylate (EMA) and ethylene-n-butyl acrylate-glycidyl-methacrylate (EBA-GMA). SEM and DSC analyses indicated that these ethylene copolymers were thermodynamically immiscible with phase separation in the form of 1–5?µm sized round domains in the PLA matrix. Rubber toughening mechanisms of EVA, EMA and EBA-GMA were very effective to improve ductility and toughness of PLA significantly. Depending on the type and content of the ethylene copolymers, the highest increases in % elongation at break, Charpy impact toughness and G_IC fracture toughness values of PLA were as much as 160, 320 and 158%, respectively. Although there were no detrimental effects of using EVA, EMA and EBA-GMA on the thermal properties of PLA, they resulted in certain level of reductions in stiffness, strength and hardness values.     

Morphologies and mechanical properties of polylactide/thermoplastic polyurethane elastomer blends

To explore a potential method for improving the toughness of a polylactide (PLA), we used a thermoplastic polyurethane (TPU) elastomer with a high strength and toughness and biocompatibility to prepare PLA/TPU blends suitable for a wide range of applications of PLA as general‐purpose plastics. The structure and properties of the PLA/TPU blends were studied in terms of the mechanical and morphological properties. The results indicate that an obvious yield and neck formation was observed for the PLA/TPU blends; this indicated the transition of PLA from brittle fracture to ductile fracture. The elongation at break and notched impact strength for the PLA/20 wt %TPU blend reached 350% and 25 KJ/m², respectively, without an obvious drop in the tensile strength. The blends were partially miscible systems because of the hydrogen bonding between the molecules of PLA and TPU. Spherical particles of TPU dispersed homogeneously in the PLA matrix, and the fracture surface presented much roughness. With increasing TPU content, the blends exhibited increasing tough failure. The J‐integral value of the PLA/TPU blend was much higher than that of the neat PLA; this indicated that the toughened blends had increasing crack initiation resistance and crack propagation resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Poly(lactic acid)/low‐density polyethylene blends and its nanocomposites based on sepiolite

Poly(lactic acid) (PLA) nanocomposite ternary blends based on unmodified sepiolite were prepared by melt blending using a corotating twin‐screw extruder. Two grafted polymers were used as compatibilizer agents, in an effort to increase the PLA tensile toughness. The influence of incorporating a low‐cost commodity low‐density polyethylene, as dispersed phase to the composites on thermal degradation, and rheological and tensile properties was studied. The morphology of the blends and composites was determined through transmission and scanning electron microscopy techniques. Results showed that the compatibilized blends prepared without clay have higher thermal degradation susceptibility and tensile toughness than those prepared with sepiolite and significant changes in complex viscosity and melt elasticity values were observed between them. The nanocomposite blends exhibited similar thermal degradation, lower tensile strength, and Young's modulus values and increased elongation at break and tensile toughness, complex viscosity, and storage modulus compared with those of the nanocomposite of PLA. These results are related to the clay dispersion, to the type of morphology of the different blends, to the localization of the sepiolite in the different phases, the thermomechanical degradation of the PLA matrix phase during melt blending and the grafting degree of the compatibilizers used. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Plasticizing polylactide—the effect of different plasticizers on the mechanical properties

Poly(lactide) (PLA), a biodegradable aliphatic polyester with excellent property profiles for different polymer applications, will play a major role in future markets for biodegradable polymers from renewable resources. PLA is a very brittle and stiff polymer with a glass transition temperature of around 58°C. The mechanical properties of PLA are comparable to those of polystyrene, with an elasticity modulus of 3500 MPa, a maximum tensile strength of 50 MPa, and an elongation at break of 4%. To introduce PLA into other applications requiring other mechanical property profiles, especially higher flexibility and higher impact resistance, it is necessary to use plasticizers. In this study the influence of several biocompatible plasticizer systems on the mechanical properties of PLA is determined. Poly(ethylene glycol), glucosemonoesters and partial fatty acid esters are introduced at 2.5, 5, and 10 wt% into polylactide. The mechanical properties, such as impact strength and the stress-strain-interrelationship of tensile tests, show changes, which are discussed.     

丙烯酸酯接枝改性天然橡胶增韧聚乳酸

通过在天然橡胶(NR)分子链上接枝甲基丙烯酸甲酯(MMA)和丙烯酸丁酯(BA),制备了三种丙烯酸酯接枝改性NR:NR-g-PMMA,NR-g-PBA和NR-g-(PMMA,PBA)。采用核磁共振氢谱对三种接枝物进行了化学结构鉴定。将接枝改性后的NR和未改性的NR与PLA采用哈克密炼机熔融共混,分别制备了PLA/NR,PLA/NR-gPMMA,PLA/NR-g-PBA和PLA/NR-g-(PMMA,PBA)共混物,研究了接枝改性NR和未改性NR含量对共混物力学性能和热性能的影响。各共混物的拉伸弹性模量和拉伸强度均随接枝改性NR和未改性NR含量的增加而降低,断裂伸长率和缺口冲击强度随接枝改性NR和未改性NR含量的增加而提高。其中,PLA/NR-g-PBA共混物的断裂伸长率和缺口冲击强度比其它共混物提高的幅度大,当NR-g-PBA的质量分数为5%时,PLA/NR-g-PBA共混物的断裂伸长率达到78%,缺口冲击强度为5.2 k J/m2,而纯PLA的断裂伸长率仅为7.7%,缺口冲击强度为2.5 k J/m2,说明NR接枝分子柔顺性较高的BA更有利于促进其与PLA共混物的韧性提高。热分析结果表明,PLA/NR-gPBA共混物的热稳定性相比于纯PLA也有所提高。     

Aligned unidirectional PLA/bacterial cellulose nanocomposite fibre reinforced PDLLA composites

In an effort to enhance the properties of polylactide (PLA), we have developed melt-spinning techniques to produce both PLA/nanocellulose composite fibres, and a method akin to layered filament winding followed by compression moulding to produce self-reinforced PLA/nanocellulose composites. Poly(L-lactide) (PLLA) fibres were filled with 2 wt.% neat and modified bacterial cellulose (BC) in an effort to improve the tensile properties over neat PLA fibres. BC increased the viscosity of the polymer melt and reduced the draw-ratio of the fibres, resulting in increased fibre diameters. Nonetheless, strain induced chain orientation due to melt spinning led to PLLA fibres with enhanced tensile modulus (6 GPa) and strength (127 MPa), over monolithic PLLA, previously measured at 1.3 GPa and 61 MPa, respectively. The presence of BC also enhanced the nucleation and growth of crystals in PLA. We further produced PLA fibres with 7 wt.% cellulose nanocrystals (CNCs), which is higher than the percolation threshold (equivalent to 6 vol.%). These fibres were spun in multiple, alternating controlled layers onto spools, and subsequently compression moulded to produce unidirectional self-reinforced PLA composites consisting of 60 vol.% PLLA fibres reinforced with 7 wt.% CNC in a matrix of amorphous PDLLA, which itself contained 7 wt.% of CNC. We observed improvements in viscoelastic properties of up to 175% in terms of storage moduli in bending. Furthermore, strains to failure for PLLA fibre reinforced PDLLA were recorded at 17%.     

Mechanical behaviour of a low-clay translucent whiteware

A novel low-clay translucent whiteware body, using mostly non-plastic prefired materials and only a small amount of clay, was fabricated by slip casting and the effect of slip's solid content and sintering temperature on the mechanical behaviour was investigated. The degree of densification in the sintered specimens was determined by measuring the bulk density. The mechanical behaviour was determined by measuring the flexural strength and fracture toughness. Young's modulus and hardness were also measured. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were carried out to analyse the microstructure.The flexural strength and fracture toughness increase with both increasing the slip's solid content and the sintering temperature up to a certain level, but further increase in solid content and sintering temperature had an adverse effect on the properties. The maximum flexural strength (∼135 MPa) and fracture toughness (∼1.85 MPa m^1/2) values were attained with specimens produced from a slip having 45 vol.% solid content at a sintering temperature of 1350 °C. It was found that the amount and distribution of closed pores, their size and possible link with each other control the flexural strength and fracture toughness of the low-clay translucent whiteware.     

PLA/PCL/滑石粉复合材料的制备与性能

在聚乳酸(PLA)中添加不同含量的聚己内酯(PCL)和滑石粉,同时添加增容剂柠檬酸三丁酯(TBC),通过熔融共混制备一系列PLA/PCL/滑石粉复合材料。主要研究了PCL、滑石粉以及TBC对PLA力学性能和结晶性能的影响。结果表明,PCL提高了PLA的韧性,但降低了强度,滑石粉主要起到了增强作用,但降低了PLA韧性,而将两者共同添加到PLA中可以起到一定的增强增韧作用,其异相成核作用也提高了PLA的结晶度。增容剂TBC的加入,改善了PLA和PCL的相容性,提高PCL的增韧效果以及复合材料的结晶度,但略微降低了PLA的拉伸强度。当PCL和滑石粉质量分数均为10%且加入0.5份的TBC后,PLA/PCL/滑石粉复合材料的断裂伸长率、拉伸强度、结晶度分别为13.3%,61.6 MPa,43.0%,相比纯PLA分别提高了533%,2%,73.4%。     

Adhesive Evaluation for New Forms of LARCTM-TPI

LARC^TM-TPI is a linear aromatic polyimide that was developed at NASA Langley Research Center in the 1970's and subsequently licensed to Mitsui Toatsu Chemicals, Inc., (MTC) in Japan. This company has made it easier to process for use in application as a structural adhesive or as a composite matrix resin. The present forms that exist are (1) high melt viscosity or Low Flow Grade (LFG); (2) medium melt viscosity or Medium Flow Grade (MFG); and (3) low melt viscosity or High Flow Grade (HFG). As expected, the low melt viscosity material is the easiest to process but has poor toughness; the high melt viscosity material is very tough but is more difficult to process. Because of these two extreme situations we have worked closely with MTC to develop an optimized system. This work has resulted in the medium melt viscosity material as well as two other modified or blended medium-flow variations.

These novel forms of LARC^TM-TPI have resulted in adhesives that can be melt processed at pressures as low as 0.01 MPa (15 psi) at temperatures between 343–371°C (650–700°F). Evaluation of adhesive performance has been accomplished using lap shear specimens and evaluating flow, wet out and shear strength. Initial strengths for these optimized materials range from 20.7–41.4 MPa (3000–6000 psi) at room temperature and 13.8–20.7 MPa (2000–3000 psi) at elevated test temperatures.     

Nanoclay Reinforced Self‐Cross‐Linking Poly(N‐Hydroxyethyl Acrylamide) Hydrogels with Integrated High Performances

Despite recent significant progress in fabricating tough hydrogels, it is still a challenge to realize high strength, large stretchability, high toughness, rapid recoverability, and good self‐healing simultaneously in a single hydrogel. Herein, Laponite reinforced self‐cross‐linking poly(N‐hydroxyethyl acrylamide) (PHEAA) hydrogels (i.e., PHEAA/Laponite nanocomposite [NC] gels) with dual physically cross‐linked network structures, where PHEAA chains can be self‐cross‐linked by themselves and also cross‐linked by Laponite nanoplatelets, demonstrate integrated high performances. At optimal conditions, PHEAA/Laponite NC gels exhibit high tensile strength of 1.31 MPa, ultrahigh tensile strain of 52.23 mm mm^?1, high toughness of 2238 J m^?2, rapid self‐recoverability (toughness recovery of 79% and stiffness recovery of 74% at room temperature for 2 min recovery without any external stimuli), and good self‐healing properties (strain healing efficiency of 42%). The work provides a promising and simple strategy for the fabrication of dual physically cross‐linked NC gels with integrated high performances, and helps to expand the fundamentals and applications of NC gels.