Mechanical,thermal, and dielectric properties of poly(lactic acid)/chitosan nanocomposites

Poly(lactic acid) (PLA) loaded with various levels of chitosan nanoparticles (CsNP) (0–5.0%) were prepared by twin‐screw extrusion. The nanocomposites were investigated based on their morphology, thermal, mechanical and dielectric properties. The SEM morphology showed that CsNP was dispersed uniformly in the PLA matrix. Thermal analysis through DSC revealed that the cold crystallization temperature of PLA in the case of nanocomposites slightly decreased with increasing content of CsNP; indicating a limit nucleating effect of CsNP. TGA analysis revealed that the incorporation CsNP slightly decreased the thermal stability of the PLA matrix. The mechanical analysis indicated that the incorporation of the CsNP in the PLA matrix improved the elongation and the impact strength, but decreased the tensile strength. The dielectric properties of these materials have been investigated for the α‐relaxation process as a function of the temperature and frequency. The α‐relaxation process was analyzed with Vogel–Fulcher–Tamman and Havriliak–Negami models and fitting parameters and their evolution were obtained. POLYM. ENG. SCI. 56:987–994, 2016. © 2016 Society of Plastics Engineers     

Enhanced mechanical and thermal properties of graphene nanoplatelets-reinforced polyamide11/poly(lactic acid) nanocomposites

The present paper aims to obtain a sustainable nanocomposite by using bio-based polyamide 11 and biodegradable poly (lactic acid) blend as matrix and graphene nanoplatelets (GNP) as nanofiller. GNP was incorporated in the PA11/PLA blend matrix in the ratio of 0.5-1-3-5-10 wt% through the twin-screw extruder. The crystallinity of PA11 in the blend, which was 12.9%, increased with the inclusion of GNP, and the highest crystallinity value was observed at 20% for the 1GNP sample. The crystallinity of PLA in the blend, which was 2.3%, increased to 4.6% with 5 wt% GNP addition. The inclusion of GNP to PA11/PLA improved the thermal degradation temperatures and increase the char residue. Also, increments were observed for storage modulus, loss modulus, and glass transition temperature of the matrix with the inclusion of GNP. The addition of GNP caused the tensile strength of the matrix to increase first and then decrease at higher amounts due to the agglomerations. 0.5–1 wt% GNP increased tensile strength by 10% and 5%, respectively. Increasing the amount of GNP to 10 wt% led to a sharp decrease in tensile strength by 24%. Overall, GNP is a suitable nanofiller to enhance the thermal and mechanical features of the PA11/PLA blend.     

Microstructure,rheological behavior,and properties of poly(lactic acid)/poly(butylene succinate)/organoclay nanocomposites

Nanocomposites made of poly(lactic acid), poly(butylene succinate), and organically modified montmorillonite were prepared by melt blending in a twin screw extruder. The influence of the organoclay content on nanocomposite properties was investigated. The nanocomposite structure has been characterized by various techniques at different scales. X‐ray diffraction showed an intercalated structure whereas rheological investigations in small amplitude oscillatory shear indicated a partial exfoliation. It was also shown that organoclay was evenly dispersed in the matrix even though some large aggregates were also observed. The mechanical properties of nanocomposites were measured in uniaxial tensile test. Oxygen and water vapor permeability was also characterized. It was shown that dispersed organoclay and aggregates have a direct impact on mechanical properties and permeability. An increase of Young's modulus by 41% and a decrease of permeability by 40% could be obtained with 7 wt % organoclay. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40364.     

Kinetics of water absorption and thermal properties of poly(lactic acid)/organomontmorillonite/poly(ethylene glycol) nanocomposites

Poly(lactic acid) (PLA)/organomontmorillonite (OMMT) nanocomposites were prepared by a melt intercalation technique. The effects of OMMT and poly(ethylene glycol) (PEG) on the thermal properties and water absorption behavior of PLA were investigated. The melting temperature and degree of crystallinity were comparable for the PLA and its nanocomposites. The glass transition temperature and crystallization temperature of PLA were decreased by the addition of PEG. X‐ray diffraction results revealed the formation of PLA nanocomposites, as the OMMT was partly intercalated and partly exfoliated. The maximum moisture absorption of PLA was increased in the presence of PEG and the diffusivity of the PLA nanocomposites decreased with increasing concentrations of PEG. However, the activation energy of the nanocomposites increased as the loading of PEG increased. These results indicated that the incorporation of OMMT and PEG enhanced the water‐barrier properties of the PLA. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Structural evaluation and thermal properties of poly(lactic acid) and different synthetic micas nanocomposites

Two types of organophilic synthetic micas were used to prepare poly(lactic acid) (PLA) nanocomposites. The effect of both micas at different concentrations were evaluated and correlated to the nanocomposite structure and thermal properties. Nanocomposites containing 3, 5, and 7 wt% of mica were obtained by mixing the components in the melt state at different conditions of temperature, rotor speed, and contacting time. The mica Somasif MAE showed the higher affinity with PLA and caused a slight variation in the thermal properties. Nevertheless, the nanocomposite presented a lower‐degradation temperature than the Somasif MPE alone. Despite no evidence of complete exfoliation, intercalation was noted in the composites obtained from the mica MAE. The organophilic mica Somasif MPE, which contains a high amount of intercalant, had a more significant influence on the composite properties, decreasing the T_g, and the crystallization temperature on heating, due to the plasticizing effect of the intercalant. POLYM. COMPOS.,, 2012. © 2012 Society of Plastics Engineers     

Morphology,thermal, and dynamic mechanical properties of poly(lactic acid)/sisal whisker nanocomposites

Sisal whiskers were used as biobased nanofillers to prepare poly(lactic acid) (PLA)‐based nanocomposites. The whiskers were prepared from sisal fibers via sulfuric acid hydrolysis. Freeze drying of the aqueous whisker suspension was carried out to obtain loosely packed dry sisal whiskers. The nanocomposites were prepared by melt mixing, followed by hot melt pressing. The effect of the freeze drying of the nanofibers, the treatments of the samples with maleic anhydride (MA)/dicumyl peroxide (DCP) and with DCP, and the premixing of the powdered components on the dispersion of the whiskers in the PLA matrix and on the morphology, as well as the thermal and dynamic mechanical properties, of the resultant nanocomposites were investigated. Transmission electron microscopy micrographs show that the acid hydrolysis has led to separation of the whiskers, which had an approximate length and diameter of 195 and 15 nm, respectively. The TEM images of the nanocomposites show similar dispersion of the whiskers in the PLA matrix, whether untreated or MA/DCP or DCP treated. It was found that the crystallization behavior of the PLA matrix changed somewhat depending on whether the samples were treated or not. The thermogravimetric analysis results show a slight decrease in the thermal stabilities of the untreated and the MA/DCP‐treated nanocomposite samples compared to that of the neat PLA, whereas the DCP treatment slightly improved the thermal stability of the nanocomposites. The storage modulus of the nanocomposites increased over the investigated temperature region, and the incorporation of sisal whiskers reduced the intensity of the glass transition at 67°C. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

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.     

Morphology and thermal properties of poly(L‐lactic acid)/organoclay nanocomposites

A modified clay was used to prepare poly(L ‐lactic acid)/clay nanocomposite dispersions. X‐ray diffraction and transmission electron microscopy experiments revealed that poly(L ‐lactic acid) was able to intercalate the clay galleries. IR spectra of the poly(L ‐lactic acid)/clay nanocomposites showed the presence of interactions between the exfoliated clay platelets and the poly(L ‐lactic acid). Thermogravimetric analysis and differential scanning calorimetry were performed to study the thermal behavior of the prepared composites. The properties of the poly(L ‐lactic acid)/clay nanocomposites were also examined as functions of the organoclay content. The exfoliated organoclay layers acted as nucleating agents, and as the organoclay content increased, the crystallization temperature increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The morphology,rheological, and mechanical properties of wood flour/starch/poly(lactic acid) blends

An entirely biosourced blend composed of poly(lactic acid) (PLA), starch, and wood flour (WF) was prepared by a co‐extruder with glycerol as a plasticizer. The morphology, rheological properties, and mechanical properties of the WF/starch/PLA blends were comprehensively analyzed. The results showed that with the decrease of the starch/WF ratio, the morphology experienced a large transformation, and the compatibility of the blends was found to be superior to other blends, with a starch/wood flour ratio of 7/3. The dynamic mechanical thermal analysis (DMA) results demonstrated the incompatibility of the components in WF/starch/PLA blends. Following the decrease of the starch/WF ratio, the storage modulus (G″) and the complex viscosity (η*) of the blends increased. The mechanical strength first increased, and then decreased with the increase of the WF concentration. The water absorption results showed that the water resistance of the blends was reduced with the lower starch/WF ratio. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44743.     

Effect of clay type and loading on thermal,mechanical properties and biodegradation of poly(lactic acid) nanocomposites

PLA nanocomposites based on two different clays (CLO30B and SOMMEE) at 5 and 10 wt.% clay loading were prepared by melt-blending, obtaining a good level of clay dispersion as well as considerable thermo-mechanical improvements in PLA, according to WAXS, SEM, TEM, DMTA and tensile strength analysis.Addition of clays induced PLA crystallization by nucleation, especially upon addition of SOMMEE, promoting kinetics and extent of crystallization of the polymer, especially at high clay content. Concerning the thermal and mechanical properties, the highest improvements in PLA matrix were obtained upon 10% clay addition, especially SOMMEE, becoming more noticeable with increasing temperature.An effective degradation of PLA and nanocomposites in compost at 40 °C was also achieved. It was found that addition of nanoparticles, especially SOMMEE, accelerated the degradation process of PLA, particularly at higher clay content, probably due to catalysis by the hydroxyl groups belonging to the silicate layers surface and/or to their organic modifier.     

Mechanical and rheological properties of epoxidized soybean oil plasticized poly(lactic acid)

Poly(lactic acid) (PLA) is a well known biodegradable thermoplastic with excellent mechanical properties that is a product from renewable resources. However, the brittleness of PLA limits its general applications. Using epoxidized soybean oil (ESO) as a novel plasticizer of poly(lactic acid), the composite blend with the twin‐screw plastic extruder at five concentrations, 3, 6, 9, 12, and 15 wt %, respectively. Compared with pure PLA, all sets of blends show certain improvement of toughness to different extents. The concentration with 9 wt % ESO increases the elongation at break about 63%. The melt flow rates of these blends with respect to different ESO ratio have been examined using a melt flow indexer. Rheological behaviors about shear viscosity and melt strength analysis are discussed based on capillary rheology measurements. The tensile strength and melt strength of the blends with 6 wt % ESO simultaneity reach the maximums; whereas the elongation at break of the blends is the second highest level. ESO exhibits positive effect on both the elongation at break and melt strength. The results indicate that the blend obtained better rheological performance and melt strength. The content of 6 wt % ESO in PLA has been considered as a better balance of performance. The results have also demonstrated that there is a certain correlation between the performance in mechanical properties and melt rheological characterization for the PLA/ESO blends.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

Dynamic mechanical and thermal properties of plasticized poly(lactic acid)

The blends of low molecular weight triacetin (TAC) and oligomeric poly(1,3‐butylene glycol adipate) (PBGA) were used as multiple plasticizers to lubricate poly(lactic acid) (PLA) in this study. The thermal and mechanical properties of plasticized polymers were investigated by means of dynamic mechanical analysis and differential scanning calorimetry. Atomic force microscopy (AFM) was used to analyze the morphologies of the blends. Multiple plasticizers were effective in lowering the glass transition temperature (T_g) and the melting temperature (T_m) of PLA. Moreover, crystallinity of PLA increased with increasing the content of multiple plasticizers. Tensile strength of the blends decreased following the increasing of the plasticizers, but increased in elongation at break. AFM topographic images showed that the multiple plasticizers dispersed between interfibrillar regions. Moreover, the fibrillar crystallite formed the quasicrosslinkings, which is another cause for the increase in elongation at break. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1583–1590, 2006     

Synthesis and thermal properties of telechelic poly(lactic acid) ionomers

Telechelic poly(lactic acid) (PLA) ionomers were synthesized using a chemical recycling process. A transesterification reaction between a commercial PLA and 2-hydroxyethyl methacrylate or ethylene glycol was used to produce a hydroxy-terminated PLA. The hydroxy-terminated PLA was then reacted with itaconic anhydride to produce terminal carboxylic acid groups, which were neutralized with appropriate metal acetates to produce Na-, Li-, K-, Zn-, Ca- and Y-ω- and α,ω-telechelic PLA ionomers. ¹H NMR spectroscopy was used to confirm the presence of the itaconic acid end-groups and FTIR spectroscopy was used to quantify the extent of neutralization. The addition of the ionic groups increased the glass transition (T_g), and T_g increased as the strength of the ion-pair increased. The ionic groups suppressed crystallinity, especially when multivalent cations were used.     

Preparation and thermomechanical properties of nanocrystalline cellulose reinforced poly(lactic acid) nanocomposites

A two‐step process was developed to prepare nanocrystalline cellulose (NCC) reinforced poly(lactic acid) (PLA) nanocomposites using polyethylene glycol (PEG) as a compatibilizer. It was composed of solvent mixing and melt blending. The NCC was well dispersed in the PLA matrix. A network was formed at high NCC‐to‐PEG ratio at which the amount of the PEG was not enough to cover all the surfaces of the NCC. The formation of the network was confirmed by the occurrence of a plateau for the storage modulus at low frequency. The incorporation of the PEG and NCC could improve the crystallinity of the PLA. The elongation at break increased from 11.0% for the neat PLA to 106.0% for the composites including 6 wt % NCC, impact strength was improved from 0.864 to 2.64 kJ m^?2 and tensile strength did not change significantly for the same 6 wt % NCC composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44683.     

Studies on morphologies and thermal properties of poly(lactic acid)/polycaprolactone/organic‐modified montmorillonite nanocomposites

Poly(lactic acid)/organic montmorillonite (PLA/OMMT) nanocomposites were prepared via twin‐screw extrusion. Montmorillonite (MMT) was firstly organically modified to improve the compatibility between polyester and MMT. The effects of ratio between PLA and OMMT and the addition of polycaprolactone (PCL), as a compatilizer, on the properties of PLA/OMMT nanocomposites were studied. The morphology and the properties of the nanocomposites were characterized by XRD, DSC, and TEM. Using OMMT, the intercalated structure was formed during the extrusion process and the OMMT interlayers space was enlarged. More OMMT content was apt to form thicker structure with more stacked individual silicate layers, which led to lower degree of crystallinity of PLA. It showed that 1 phr OMMT could result in the largest interlayers space and the best crystallization state. PCL can effectively increase the binding force between two phases and improve the order of the nanocomposites. In addition, the annealing after treatment can form regular structure and enhance the thermal properties of nanocomposites. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Plasticized poly(lactic acid) with low molecular weight poly(ethylene glycol): Mechanical,thermal, and morphology properties

Poly(lactic acid) PLA was plasticized with low molecular weight poly(ethylene glycol) PEG‐200 to improve the ductility of PLA, while maintaining the plasticizer content at maximum 10 wt%. Low molecular weight of PEG enables increased miscibility with PLA and more efficient reduction of glass transition temperature (T_g). This effect is enhanced not only by the low molecular weight but also by its higher content. The tensile properties demonstrated that the addition of PEG‐200 to PLA led to an increase of elongation at break (>7000%), but a decrease of both tensile strength and tensile modulus. The plasticization of the PLA with PEG‐200 effectively lowers T_g as well as cold‐crystallization temperature, increasing with plasticizer content. SEM micrographs reveal plastic deformation and few long threads of a deformed material are discernible on the fracture surface. The use of low molecular weight PEG‐200 reduces the intermolecular force and increases the mobility of the polymeric chains, thereby improving the flexibility and plastic deformation of PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4576–4580, 2013     

Effect of organoclay on non-linear rheological properties of poly(lactic acid)/poly(caprolactone) blends

The nonlinear viscoelastic properties of PLA/PCL blends with and without clay (montmorillonite, MMT) under large amplitude oscillatory shear (LAOS) flow were investigated. The G′ and G″ as a function of strain amplitude, Lissajous plots and FT-rheology methods were used to interpret nonlinear behavior of PLA/PCL blends with and without MMT. Additionally, scanning electron microscopy (SEM) images of PLA/PCL with MMT blends were taken to investigate the effects of clay on the internal structure of the PLA/PCL blends. A relationship between morphological changes and linear and nonlinear rheological properties was observed. SEM image analysis revealed that clay acted as a compatibilizer and then reduced the size of droplets in the PCL domain of the PLA matrix. As a result, nonlinear properties sensitively reflect morphological changes with increasing MMT amount. The nonlinear rheological properties of PLA/PCL/MMT/metallocene-LLDPE (mLLDPE) were also investigated when mLLDPE was used as an impact modifier to improve mechanical properties, and the nonlinear rheological properties of PLA/PCL/MMT and PLA/PCL/MMT/mLLDPE were also compared.     

Effect of organoclay chemistry and morphology on properties of poly(lactic acid) nanocomposites

Poly(lactic acid) (PLA) nanocomposites with different layered organoclays (variation in the surface treatment of silicate) and one special nanofiller (mixed mineral thixotrope) were melt-compounded using a semi-industrial co-rotating twin-screw extruder. Effects of the silicate surface treatment and shape on the structure as well on processing and utility properties in PLA matrix were investigated. The structural changes in polymer matrix were evaluated from dynamic experiments in the shear flow using low-amplitude oscillatory measurements. Moreover, new approach for morphological investigation of nanocomposites using small-angle X-ray scattering was presented. Concerning utility properties, tests of mechanical and barrier properties were performed to compare enhancement of PLA matrix due to incorporation of different nanoparticles. Surprisingly, filling the PLA matrix with mixed mineral thixotrope resulted into very high material performance (in particular, significant improvement in barrier properties) compared to filling with commercial layered silicates. In this way, new type of nanofiller for PLA applications has been successfully tested.