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.     

Highly Tough and Thermally Stable Polylactide Blends Compatibilized with Glycidyl Methacrylate-Grafted Polypropylene

To attain eco-friendly and sustainable polylactide (PLA) materials possessing highly enhanced toughness, thermal stability, and processability without significant loss in elastic modulus, for the first time, PLA-dominant blends with 1–30 wt% glycidyl methacrylate-grafted polypropylene (PPGMA) loadings are fabricated via an efficient masterbatch melt-compounding process. For the purpose, PPGMA is fabricated via in situ grafting reaction of PP with GMA and styrene. The scanning electron microscope images reveal that PLA/PPGMA blends do not show recognizable phase-separated domains, unlike immiscible PLA/PP blends. The Fourier-transform infrared spectroscopic and melt-rheological analyses support the presence of specific interactions between PLA and PPGMA as well as the compatibilizing effect of PPGMA-g-PLA formed during the melt-compounding. The thermal analyses demonstrate that PPGMA component accelerates the crystallization of PLA in the blends and that the thermal decomposition temperatures of PLA/PPGMA blends are higher than those of neat PLA and PPGMA components. The dynamic mechanical analysis shows that a maximum storage modulus is attained for PLA-dominant blend with 30 wt% PPGMA. Noticeably, the impact strength (≈305.6 J m⁻¹) of PLA-dominant blend with only 5 wt% PPGMA loading is almost three times higher than that (≈111.6 J m⁻¹) of neat PLA and it is very comparable to the value (≈316.9 J m⁻¹) of neat PP.     

Toughening of poly(lactide) using polyethylene glycol methyl ether acrylate: Reactive versus physical blending

To design high‐performance poly(lactide)‐based materials (PLA‐based) with improved toughness, two approaches based on the reactive extrusion (REx) process are investigated and compared in the present study. The first approach relies upon a two‐step procedure using a REx‐polymerized poly(ethylene glycol) methyl ether acrylate, i.e., poly(AcrylPEG), as a highly‐branched and compatible impact modifier for PLA. The free‐radical polymerization proves to be very efficient with a peroxide initiator concentration of 1 wt%. The as‐produced poly(AcrylPEG) is then melt‐blended with PLA by extrusion. The resulting materials exhibit largely increase impact resistance (ca. 35 kJ/m²) in presence of 20 wt% poly(AcrylPEG) in comparison with neat PLA (2.7 kJ/m²), while moderate ductility (tensile elongation at break <40%) and limited plasticization effect are observed. The second “one‐step” approach consists in in situ grafting of AcrylPEG onto PLA backbone via a one‐stage REx. The resulting materials exhibit substantially improved impact resistance (ca. 102 kJ/m²) for AcrylPEG loading of 20 wt%, high ductility (tensile elongation at break of ca. 150%) and efficient plasticization. A detailed characterization of the morphology of the materials has been performed using PF‐QNM‐AFM to better elucidate the structure‐property relationships. POLYM. ENG. SCI., 55:1408–1419, 2015. © 2015 Society of Plastics Engineers     

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     

Synthesis and characterization of bis(4‐cyanato 3,5‐dimethylphenyl) naphthyl methane/epoxy/glass fiber composites

Bis(4‐cyanato 3,5‐dimethylphenyl) naphthylmethane was prepared by treating CNBr with bis(4‐hydroxy 3,5‐dimethylphenyl) naphthylmethane in the presence of triethylamine at −5 to 5°C. The dicyanate was characterized by FT‐IR and NMR techniques. The prepared dicyanate was blended with commercial epoxy resin in different ratios and cured at 120°C for 1 hr, 180°C for 1 hr, and post cured at 220°C for 1 hr using diamino diphenyl methane (DDM) as curing agent. Castings of neat resin and blends were prepared and characterized by FT‐IR technique. The morphology of the blends was evaluated by SEM analysis. The composite laminates were also fabricated from the same composition using glass fiber. The mechanical properties like tensile strength, flexural strength, and fracture toughness were measured as per ASTMD 3039, D 790, and D 5528, respectively. The tensile strength increased with increase in cyanate content (3, 6, and 9%) from 322 to 355 MPa. The fracture toughness values also increased from 0.7671 kJ/m² for neat epoxy resin to 0.8615 kJ/m² for 9% cyanate ester epoxy modified system. The thermal properties were also studied. The 10% weight loss temperature of pure epoxy is 358°C and it increased to 398°C with incorporation of cyanate ester resin. The incorporation of cyanate ester up to 9% loading level does not affect the T_g to a very great extent. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Super-tough poly(lactic acid) using a fully bio-based polyester containing malic acid via in-situ interfacial compatibilization

Reactive interfacial compatibilization is the most efficient way to prepare super-tough poly (lactic acid) (PLA) materials. Introducing a post-reactive group into a toughening agent that can react with PLA is the key issue. Herein, we reported a series of fully bio-based polyesters (PBSePM) synthesized with sebacic acid, diethyl malate, 1,3-propanediol, and 1,4-butanediol via transesterification in one pot. Super-tough PLA materials can be obtained by reactively blending with PBSePM in the presence of hexamethylene diisocyanate (HDI). In the processing, the side hydroxyl group of the PBSePM reacted with HDI and formed polyurethane elastomer to improve the toughness of PLA. Moreover, the in-situ formed PLA-g-PBSePM grafted copolymer enhanced the interfacial adhesion. With increasing diethyl malate moiety in PBSePM, the PBSePM phase morphology transformed from co-continuous phase structure to semi-continuous and “sea-island” phase structure. When adding 20 wt% PBSePM, all PLA/PBSePM blends have a notched impact strength higher than 53 kJ m⁻², suggested a super toughness effect. Maximum impact strength of 83 kJ m⁻² was realized while the PBSePM containing 20% diethyl malate moiety. In addition, super-tough PLA materials can be achieved by only adding 15 wt% PBSePM20, exhibited a highly efficient toughening effect.     

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) formulations with improved toughness by physical blending with thermoplastic starch

This work focuses on poly(lactic acid) (PLA) formulations with improved toughness by physical blending with thermoplastic maize starch (TPS) plasticized with aliphatic–aromatic copolyester up to 30 wt %. A noticeable increase in toughness is observed, due to the finely dispersed spherical TPS domains in the PLA matrix. It is worth to note the remarkable increase in the elongation at break that changes from 7% (neat PLA) up to 21.5% for PLA with 30 wt % TPS. The impact‐absorbed energy is markedly improved from the relatively low values of neat PLA (1.6 J m^?2) up to more than three times. Although TPS is less thermally stable than PLA due to its plasticizer content, in general, PLA/TPS blends offer good balanced thermal stability. The morphology reveals high immiscibility in PLA/TPS blends, with TPS‐rich domains with an average size of 1 μm, finely dispersed which, in turn, is responsible for the improved toughness. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45751.     

Synthesis and characterization of bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane/epoxy/glass fiber composites

Bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane was prepared by treating CNBr with bis(4‐hydroxy‐3,5‐dimethylphenyl)anisylmethane and blended with commercial epoxy resin in different ratios and cured at 120°C for 2 h, 180°C for 1 h, and postcured at 220°C for 1 h using diamino diphenyl methane as curing agent. Castings of neat resin and blends were prepared and characterized. The composite laminates were also fabricated with glass fiber using the same composition. The tensile strength of the composites increased with increase in cyanate content (3, 6, and 9%) from 322 to 355 MPa. The fracture toughness values also increased from 0.7671 kJ/m², for neat epoxy resin, to 0.8615 kJ/m², for 9% cyanate ester‐modified epoxy system. The 10% weight loss temperature of pure epoxy (358°C) was increased to 390°C by the incorporation of cyanate ester resin. The incorporation of cyanate ester up to 9% in the epoxy resin increases the T_g from 143 to 147°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reactive compatibilization of high‐impact poly(lactic acid)/ethylene copolymer blends catalyzed by N,N‐dimethylstearylamine

The inherent brittleness of poly(lactic acid) (PLA) limits its wide application in many fields. Here, high‐impact PLA/ethylene–methyl acrylate–glycidyl methacrylate random terpolymer (EMA–GMA) blends were prepared with the addition of a small amount of N,N‐dimethylstearylamine (DMSA) catalyst. It was found that the notched impact resistance of various PLA/EMA–GMA blends could be considerably improved by adding DMSA. In particular, the notched Izod impact strength of the blend with 20 wt% EMA–GMA increased from 35.6 to 83.5 kJ m^?2 by adding 0.2 wt% DMSA. Reactive compatibilization between PLA and EMA–GMA with DMSA was studied using Fourier transform infrared spectroscopy. The results indicated that DMSA promoted the reaction between the epoxide group of EMA–GMA and end groups (–OH, –COOH) of PLA. This considerably improved the interfacial adhesion, leading to better wetting of the dispersed phase by the PLA matrix and finer dispersed EMA–GMA particles. Therefore, the significant increase in notched impact strength was attributed to the effective reactive compatibilization promoted by DMSA. © 2013 Society of Chemical Industry     

Thermal,mechanical, and rheological properties of plasticized poly(L‐lactic acid)

Polylactide (PLA) is an attractive candidate for replacing petrochemical polymers because it is biodegradable. In this study, a specific PLA 2002D was melt‐mixed with a new plasticizer: glycerol monostearate (GMS). The PLA/GMS blends with different ratios were analyzed by dynamic mechanical analysis and differential scanning calorimetry. Although a slightly phase separation can be seen in DSC curves, the SEM micrographs of the impact fracture surfaces of PLA/GMS blends had a relatively good separation and this phenomenon was in good agreement with their higher impact strength. The result showed that the adding of GMS has enhanced the flexibility of PLA/GMS blends as compared to neat PLA. The relationship between complex viscosity and angular frequency of the PLA/GMS blends exhibits that the melt viscosity substantially lower than that of neat PLA. For example, at 10 rad/s, the melt viscosity of PLA/GMS (85/15) was reduced by about 7.2% compared to that of neat PLA. The impact strength was changed from 4.7 KJ/m² for neat PLA to 48.2 KJ/m² for 70/30 PLA/GMS blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Experimental assessment on potential for processiblity of carbon nanotubes/epoxy system used as nanocomposites

In this study, carboxylic acid functionalized carbon nanotubes (CNTs) were used to modify epoxy with intent to develop a nanocomposite matrix for hybrid multiscale composites combining benefits of nanoscale reinforcement with well‐established fibrous composites. CNTs were dispersed in epoxy by using high energy sonication, followed by the fabrication of epoxy/CNTs composites. The processibility of CNTs/epoxy systems was explored with respect to their dispersion state and viscosity. The dependences of viscosity, mechanical and thermomechanical properties of nanocomposite system on CNTs content were investigated. The dispersion quality and reagglomeration behavior of CNTs in epoxy and the capillary infiltration of continuous fiber with the epoxy/CNTs dispersion were characterized using optical microscope and capillary experiment. As compared with neat epoxy sample, the CNTs nanocomposites exhibit flexural strength of 126.5 MPa for 1 wt% CNTs content and impact strength of 28.9 kJ m^?2 for 0.1 wt% CNTs content, respectively. A CNTs loading of 0.1 wt% significantly improved the glass transition temperatures, T_g, of the nanocomposites. Scanning electron microscopy (SEM) was used to examine the fracture surface of the failed specimens. It is demonstrated that the properties of CNTs/epoxy system are dispersion‐dominated and interface sensitive. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Thermal, rheological, and mechanical properties of polylactide/poly(diethylene glycol adipate)

Polylactide (PLA) was plasticized with a new biodegradable macromolecular plasticizer-poly(diethylene glycol adipate) (PDEGA). The crystallization behavior, miscibility, rheological behavior, mechanical properties and phase behavior of PLA/PDEGA blends were investigated. The PDEGA lowered the glass transition temperature and the cold crystallization temperature. With an increase of PDEGA content, the break strain and impact strength increased significantly. The high break strain of 480 % and the high impact strength of 30 kJ/m² were obtained for 70/30 PLA/PDEGA blend. PDEGA was uniformly dispersed in the PLA matrix. The results indicated that PDEGA had a good plasticizing effect on PLA.     

Crystallization behavior of α‐cellulose short‐fiber reinforced poly(lactic acid) composites

The isothermal crystallization behavior of α‐cellulose short‐fiber reinforced poly(lactic acid) composites (PLA/α‐cellulose) was examined using a differential scanning calorimeter and a petrographic microscope. Incorporating a natural micro‐sized cellulose filler increased the spherulite growth rate of the PLA from 3.35 μm/min for neat PLA at 105°C to a maximum of 5.52 μm/min for the 4 wt % PLA/α‐cellulose composite at 105°C. In addition, the inclusion of α‐cellulose significantly increased the crystallinities of the PLA/α‐cellulose composites. The crystallinities for the PLA/α‐cellulose composites that crystallized at 125°C were 48–58%, higher than that of the neat PLA for ～13.5–37.2%. The Avrami exponent n values for the neat and PLA/α‐cellulose composites ranged from 2.50 to 2.81 and from 2.45 to 3.44, respectively, and the crystallization rates K of the PLA/α‐cellulose composites were higher than those of the neat PLA. The activation energies of crystallization for the PLA/α‐cellulose composites were higher than that of the neat PLA. The inclusion of α‐cellulose imparted more nucleating sites to the PLA polymer. Therefore, it was necessary to release additional energy and initiate molecular deposition. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ultrafine full-vulcanized powdered rubbers/PVC compounds with higher toughness and higher heat resistance

A new type of rigid PVC compound with higher toughness and higher heat resistance was prepared by using a new type of PVC modifier, ultrafine full-vulcanized powdered rubber (UFPR). The UFPRs used in this paper were butadiene nitrile UFPR-1 (NBR-UFPR-1) with particle size of about 150 nm and butadiene nitrile UFPR-2 (NBR-UFPR-2) with particle size of about 90 nm. Dynamic mechanical thermal analysis (DMTA) showed that glass transition temperature (T_g) of PVC in compounds increased from 77.52 °C of neat PVC to 82.37 and 85.67 °C, while the notched impact strengths increased from 3.1 kJ/m² of neat PVC to 5.2, 5.5 kJ/m², respectively. It can be found that both T_g and toughness of PVC have been improved simultaneously, and the smaller the particle size of NBR-UFPRs, the higher the T_g and the impact strength. The property could be attributed to larger interface and more interfacial interaction between NBR-UFPRs and PVC matrix. Transmission electron microscopy (TEM) showed that NBR-UFPRs could be well dispersed in PVC matrix.     

Epoxy/clay nanocomposites: further exfoliation of newly modified clay induced by shearing force of ball milling

To induce montmorillonite (MMT) to be further exfoliated and homogeneously dispersed in epoxy matrix (diglycidyl ether of bisphenol A) curing in the presence of diaminodiphenyl sulfone and obtain improved mechanical properties, a promising new method has been developed to prepare highly reinforced epoxy/MMT nanocomposites through exerting shearing force on epoxy/MMT solution by ball milling. Modifying agents, being combined with dodecylbenzyldimethylammonium chloride and meta‐xylylenediamine, were used to organically modify the clay (MMTII). Different resultant products were characterized by Fourier‐transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, etc, and the fracture surface of the mechanically tested specimens was also observed by scanning electronic microscopy. Results show that the novel MMTII possess a reactive interaction surface with the epoxy matrix. Exfoliation of the retained sandwich structure (being intercalated) or large agglomerates (undispersed MMTII) can be promoted by external shearing force of ball milling, and homogeneously dispersed MMTII nano‐sheets in epoxy matrix nanocomposites are typically observed. Mechanical properties, especially impact toughness, can be increasingly enhanced by the newly structured MMTII and ball milling. Impact strength is increased up to 48.1 kJ m^?2 from 32.1 kJ m^?2 at 3 wt% MMTII content, which is about 50 % higher than that of pristine matrix, and the flexural strength can also be enhanced by about 8 % higher. Copyright © 2004 Society of Chemical Industry     

Preparation and balanced mechanical properties of solid and foamed isotactic polypropylene/SEBS composites

This study presents a self-designed foaming apparatus and routes to manufacture foamed isotactic polypropylene (iPP) blends with uniform and dense cells, using styrene-ethylene-butadiene-styrene (SEBS) block copolymer as toughening additive. The addition of SEBS can clearly enhance the impact strength of solid iPP, iPP blends with a 20 wt% SEBS has obtained high notched impact strength of 75 kJ/m², which is ca. 16 times larger than that of neat iPP. Relatively fine microcellular iPP-SEBS foams with the average cell size of several micrometers, and the cell density of 10⁹ cells/cm³ were fabricated using a batch foaming procedure. Moreover, using our self-designed mold and compression foaming method, iPP-SEBS foams with balanced mechanical properties were produced. With the increasing of SEBS, tensile strength and flexural strength were slightly decreased, but the impact strength was increased clearly. The balanced mechanical properties between stiffness and toughness were achieved after compression foaming.     

The effect of graphene nanoplatelet thickness on the fracture toughness of Si3N4 composites

Si₃N₄ composites with 3 and 5?wt% of graphene nanoplatelet (GNP) additions were prepared by spark plasma sintering. We used both commercially available GNPs and thinner few-layer graphene nanoplatelets (FL-GNPs) prepared by further exfoliation through ball milling with melamine addition. We found that by employing thinner FL-GNPs as filler material a 100% increase in the fracture toughness of Si₃N₄/3?wt% FL-GNP composites (10.5?±?0.2?MPa?m^1/2) can be achieved as compared to the monolithic Si₃N₄ samples (5.1?±?0.3?MPa?m^1/2), and 60% increase compared to conventional Si₃N₄/3?wt% GNP composites (6.6?±?0.4?MPa?m^1/2). For 5?wt% filler content the increase of the fracture toughness was near 50% for both GNP and FL-GNP fillers. The hardness of the composites decreased with increasing GNP content. However, composites reinforced with 5?wt% of FL-GNPs displayed 30% higher Vickers hardness (12.8?±?0.2?GPa) than their counterparts comprising conventional GNP fillers (9.8?±?0.2?GPa). We attribute the enhanced mechanical properties obtained with thinner FL-GNPs to their higher aspect ratio leading to a more homogeneous dispersion, higher interface area, as well as smaller pores in the ceramic matrix.     

Effect of nanoparticles on mode‐I fracture toughness of polyurethane foams

Mode‐I fracture toughness of rigid polyurethane (PUR) foam modified with nanosize particles of different shapes and sizes have been examined using a single edge notched bend (SENB) specimen under three‐point bending configuration. The PUR foams with density of 260 kg/m³ and four different types of nanoparticles, namely, nano TiO₂ (5, 10, and 35 nm), nanoclay, carbon nanofibers (CNFs), and multiwall carbon nanotubes (MWNTs) are considered. Nanophased PUR foams are prepared through the infusion of nanoparticles into liquid PUR foam precursor in the range of 0.5–2 wt% with 0.5‐wt% increment using a sonochemical method. The linear elastic fracture mechanics (LEFM) model has been used to determine the mode‐I fracture toughness. The fracture toughness data have been validated with the plain strain fracture criteria and found to be appropriate. It is observed that the infusion of CNF at 0.5‐wt% loading shows the highest enhancement in fracture toughness (about 28%) over neat counter part. Among different sized nano TiO₂, 5 nm nanoparticles show the highest improvement (about 16%) at a doping of 1.0 wt%. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

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.