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     

Processing and characterization of poly(lactic acid) films plasticized with commercial adipates

The high brittleness of Poly(lactic acid) is a major drawback for flexible food packaging applications. The aim of this work is to evaluate the potential use of commercial adipates as PLA plasticizers to obtain transparent films with enhanced mechanical properties. Processing conditions were optimized. The effect of plasticizers was characterized by a decrease on the glass transition temperature and an increase in PLA chains mobility, which induced crystallization on heating. Thermal stability was not significantly affected, and mechanical properties showed an increase in ductility with the plasticizer content. Oxygen transmission rate was also measured to evaluate the effect of the microstructures generated by the presence of these additives in PLA‐based films. The monomeric adipate presented lack of homogeneity that makes films plasticized with this additive not useful for the intended application. Good compatibility was observed between polyadipates (up to 20 wt %) and the matrix, making them promising materials for biodegradable films manufacturing. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of citrate esters as plasticizers on the thermal and mechanical properties of poly(methyl methacrylate)

Plasticizers play a key role in the formulation of polymers and in determining their physical properties and processability. This study examines the effects of citrate esters, triethylcitrate, and triacetine as plasticizers on the thermal and mechanical properties of poly(methyl methacrylate). The samples were characterized by differential scanning calorimetry, dynamical mechanical analysis, and mechanical testing under different plasticizer contents. Both citrate esters proved to be effective as plasticizers, DSC data for the triacetine additive fits with Fox equation. Microstructure and relaxation properties were studied by dynamic mechanical analysis where loss modulus shows clearly that absorbed plasticizer shifts the α‐transition to lower temperature and β‐relaxations associated to ester side groups are unchanged even up to 30 wt % plasticizer. Mechanical properties were evaluated with an Instron testing machine. Both additives produced (1) an initial plasticization, with a decrease in tensile strength and modulus; (2) an antiplasticization, reflected as an increase in tensile strength; and modulus and (3) a final plasticization, with a notable decrease in tensile strength and modulus and an increase in elongation where a 35 wt % of triethylcitrate added to the poly(methyl methacrylate) increased in 200% its elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

An investigation of melt rheology and thermal stability of poly(lactic acid)/ poly(butylene succinate) nanocomposites

A systematic investigation of the rheological and thermal properties of nanocomposites prepared with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and organically modified layered silicate was carried out. PLA/PBS/Cloisite 30BX (organically modified MMT) clay nanocomposites were prepared by using simple melt extrusion process. Composition of PLA and PBS polymers were fixed at a ratio of 80 to 20 by wt % for all the nanocomposites. Rheological investigations showed that high clay (> 3 wt %) contents strongly improved the viscoelastic behavior of the nanocomposites. Percolation threshold region was attained between 3 and 5 wt % of clay loadings. With the addition of clay content for these nanocomposites, liquid‐like behavior of PLA/PBS blend gradually changed to solid‐like behavior as shown by dynamic rheology. Steady shear showed that shear viscosity for the nanocomposites decreased with increasing shear rates, exhibiting shear‐thinning non‐Newtonian behavior. At higher clay concentrations, pseudo‐plastic behavior was dominant, whereas pure blend showed almost Newtonian behavior. Thermogravimetric analysis revealed that both initial degradation temperature (at a 2% weight loss) and activation energy of thermal decomposition nanocomposite containing 3 wt % of C30BX were superior to those of other nanocomposites as well as to those of PLA/PBS blend. Nanocomposite having 1 wt % of C30BX did not achieve expected level of thermal stability due to the thermal instability of the surfactant present in the organoclay. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and application of a novel thermostable epoxy plasticizer based on levulinic acid for poly(vinyl chloride)

Epoxy bisphenol acid isooctyl ester (EBAIE) was synthesized and characterized by FTIR and H-NMR. EBAIE was used as poly(vinyl chloride) (PVC) plasticizer for the first time, and its addition amount was 30 wt% of PVC. The mechanical properties, thermal stability, compatibility, and decomposition activation energy of PVC blends were systematically studied. Compared to the commercial plasticizer-dioctyl phthalate (DOP), the tensile strength had been significantly increased from 30.64 to 45.07 MPa, while the elongation at break had little difference. The thermal stability analysis showed that the static stability time at 180°C had been extended from 40 to 300 min. The decomposition activation energy indicated that the EBAIE plasticized PVC was with a higher thermal stability. The extraction and volatility resistance of the novel plasticizer were superior to those of DOP.     

Reactive oxygen species-responsive degradable poly(amino acid)s for biomedical use

A series of reactive oxygen species-responsive degradable poly(amino acid)s (PAAs) was synthesized via in situ melting polycondensation. The PAAs were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and mechanical property analysis. The degradation and biocompatibility of the PAAs were also studied to evaluate their applicability as biomedical materials. The results show that the PAAs possessed semicrystalline amide structures, and the PAA melting temperature decreased gradually with increasing methionine loading. The incorporation of methionine decreased the thermal stability of the matrix, leading to decreases in both the initial and maximum degradation temperatures. The mechanical properties of the PAAs deteriorated as the content of methionine increased. The content of methionine had an obvious effect on PAA degradation, and the PAAs were responsive to the reactive oxygen-rich environment, suggesting that the incorporation of methionine is effective at improving the degradation of PAAs. The PAAs showed great in vitro and in vivo biocompatibilities. Based on the results, these polymers show promise as high-performance materials for biomedical applications.     

Barrier properties of poly(lactic acid) and its morphological changes induced by aroma compound sorption

The barrier properties of poly(lactic acid) (PLA) play a key role in food packaging applications. For their optimization, the influence of crystallinity on the barrier properties of PLA and the interaction of PLA with the aroma compound ethyl acetate were investigated. PLA film samples with various crystallinities were fabricated by flat die extrusion and thermocompression and compared to PLA Biophan^?. The degree of crystallinity had no effect on the oxygen permeability. However, an increase of crystallinity caused a decrease in ethyl acetate sorption. The sorption isotherm of ethyl acetate obtained using microgravimetry showed a steep increase with increasing aroma activity, a form which is consistent with a plasticization effect. This behaviour was verified using differential scanning calorimetry and dynamic mechanical analysis. Sorption caused a marked decrease in the glass transition temperature well below room temperature to approximately 0 °C. Furthermore, PLA underwent a solvent‐induced crystallization when equilibrated in ethyl acetate atmosphere at an activity of 0.5. The results obtained show the importance of considering possible interactions between polymer and foodstuff during the optimization step of polymeric materials for food packaging applications. Copyright © 2010 Society of Chemical Industry     

Experimental investigation on the properties of poly (L-lactic acid) vascular stent after accelerated in vitro degradation

Poly (L-lactic acid) (PLLA) vascular stents are promising to be used to treat vascular stenosis. However, the degradation of these implanted stents has a great influence on the mechanical properties. In this work, we studied the factors that can influence the mechanical properties by accelerating the degradation of PLLA stents with crimping and expansion in phosphate buffer solution (PBS) at 70°C. The typical influence factors such as the real-time weight-average molecular weight (M_w), crystallinity, surface morphologies, and mass loss of these samples were analyzed in detail. Results showed that radial strength of the stents increased from 877 to 1204 mmHg after accelerated degradation for 2 days and then decreased to almost 0 mmHg after 10 days. Meanwhile, radial stiffness showed an upward trend which is caused by the decrease in M_w, increase in crystallinity and local damage during the crimping and expansion process. Moreover, negligible mass loss of stents was observed in this period and the bulk degradation behavior predominated in the whole process.     

Morphology,crystallization, and mechanical properties of poly(ethylene terephthalate)/multiwalled carbon nanotubes composites

Poly(ethylene terephthalate)/multiwalled carbon nanotubes (PET/MWCNTs) with different MWCNTs loadings have been prepared by in situ polymerization of ethylene glycol (EG) containing dispersed MWCNTs and terephthalic acid (TPA). From scanning electronic microscopy images of nanocomposites, it can be clearly seen that the PET/MWCNTs composites with low‐MWCNTs contents (0.2 and 0.4 wt %) get better MWCNTs dispersion than analogous with high‐tube loadings (0.6 and 0.8 wt %). The nonisothermal crystallization kinetics was analyzed by differential scanning calorimetry using Mo kinetics equation, and the results showed that the incorporation of MWCNTs accelerates the crystallization process obviously. Mechanical testing shows that, in comparison with neat PET, the Young's modulus and the yield strength of the PET nanocomposites with incorporating 0.4 wt % MWCNTs are effectively improved by about 25% and 15%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of miscibility on mechanical and thermal properties of poly(lactic acid)/ polycaprolactone blends

Binary blends based on poly(lactic acid) (PLA) and polycaprolactone (PCL) were prepared by melt mixing in a twin‐screw co‐rotating extruder in order to increase the low intrinsic elongation at break of PLA for packaging applications. Although PLA and PCL show low miscibility, the presence of PCL leads to a marked improvement in the ductile properties of PLA. Various mechanical properties were evaluated in terms of PCL content up to 30 wt% PCL. In addition to tensile and flexural properties, Poisson's ratio was obtained using biaxial extensometry to evaluate transversal deformations when axial loads are applied. Very slight changes in the melt temperature and glass transition temperature of PLA are observed thus indicating the low miscibility of the PLA–PCL system. Field emission scanning electron microscopy reveals some interactions between the two components of the blend since the morphology is characterized by non‐spherical polycaprolactone drops dispersed into the PLA matrix. In addition to the improvement of mechanical ductile properties, PCL provides higher degradation rates of blends under conditions of composting for contents below 22.5% PCL. © 2016 Society of Chemical Industry     

Preparation and some properties of stereocomplex‐type poly(lactic acid)/layered silicate nanocomposites

Stereocomplex‐type poly(lactic acid)‐ [PLA]‐ based blends were prepared by solution casting of equimolar PLLA/PDLA with different amounts of organo‐modified montmorillonite. The homocrystallization and stereocomplexation of PLAs were enhanced by annealing of the blends. The stereocomplexation of PLAs, intercalation of the polymer chains between the silicates layers, and morphological structure of the filled PLAs were analyzed by wide‐angle X‐ray diffraction and transmission electron microscope. Thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and tensile test were performed to study the thermal and mechanical properties of the blends. The homo‐ and stereocomplex crystallization of neat PLLA/PDLA were enhanced by annealing. The effect of annealing on the crystallization was emphasized by the addition of clay. With this structural change, thermal stabilities properties were also improved by the addition of clay. The silicate layers of the clay were slightly stacked but intercalated and distributed in the PLA‐matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The effects of plasticizers on the dynamic mechanical and thermal properties of poly(lactic acid)

Poly(lactic acid) (PLA) was blended with five plasticizers in a batchwise mixer and pressed into films. The films were analyzed by means of dynamic mechanical analysis and differential scanning calorimetry to investigate the properties of the blends. Triacetine and tributyl citrate proved to be effective as plasticizers when blended with PLA. The glass transition temperature of PLA decreased linearly as the plasticizer content was increased. Both plasticizers were miscible with PLA to an extent of ～ 25 wt %. At this point, the PLA seemed to be saturated with plasticizer and the blends tended to phase separate when more plasticizer was added. There were also signs of phase separation occurring in samples heated at 35, 50, and 80°C, most likely because of the material undergoing crystallization. The presence of the plasticizers induced an increased crystallinity by enhancing the molecular mobility. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1227–1234, 2002     

Mechanical and thermal properties of poly(butylene succinate)/plant fiber biodegradable composite

Biodegradable polymeric composites were fabricated from poly(butylene succinate) (PBS) and kenaf fiber (KF) by melt mixing technique. The mechanical and dynamic mechanical properties, morphology and crystallization behavior were investigated for PBS/KF composites with different KF contents (0, 10, 20, and 30 wt %). The tensile modulus, storage modulus and the crystallization rate of PBS in the composites were all efficiently enhanced. With the incorporation of 30% KF, the tensile modulus and storage modulus (at 40°C) of the PBS/KF composite were increased by 53 and 154%, respectively, the crystallization temperature in cooling process at 10°C/min from the melt was increased from 76.3 to 87.7°C, and the half‐time of PBS/KF composite in isothermal crystallization at 96 and 100°C were reduced to 10.8% and 14.3% of that of the neat PBS, respectively. SEM analysis indicates that the adhesion between PBS and KF needs further improvement. These results signify that KF is efficient in improving the tensile modulus, storage modulus and the crystallization rate of PBS. Hence, this study provides a good option for preparing economical biodegradable composite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

New poly(phenylene oxide)/polystyrene blend nanocomposites with clay: Intercalation,thermal and mechanical properties

We present the first study and results on the preparation and characterization of montmorillonite clay filler based polymer blend nanocomposites of the miscible poly(phenylene oxide)/polystyrene blend. Intercalated nanocomposites, prepared by a melt‐processing method with 2–6 wt % commercially available organically modified sodium montmorillonite, have been characterized with wide‐angle X‐ray diffraction, transmission electron microscopy analysis, thermal analysis (thermogravimetric analysis and differential scanning calorimetry), and mechanical tensile tests. We show that nanocomposites can be successfully prepared in a batch mixer at temperatures much below the conditions conventionally used for this blend without organic degradation. Thermal stability is enhanced by nanoscale hybrid formation. The level of intercalation (change in the d‐spacing) does not change with the clay loading. Better dispersion of clay in the blend matrix has been observed at a low level of clay content. The nanocomposites show improved tensile modulus (by 31%) in comparison to the blend, whereas the tensile strength (stress at break) and elongation decrease in the presence of the filler with an increase in the clay loading. The Halpin–Tsai model is able to predict the modulus of the nanocomposites in very good agreement with the experimental data. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

Biodegradable poly(L‐lactic acid)/TiO2 nanocomposites: Thermal properties and degradation

Poly(L ‐lactic acid)‐titanium dioxide nanocomposites (with various loadings of TiO₂: 0.5, 1, 2, 5, and 10 wt %) were produced by solution casting method. The influence of TiO₂ on thermal properties and crystallinity of PLA was investigated by DSC and FTIR spectroscopy. The TiO₂ nano filler has no significant influence on the characteristic temperatures (T_g, T_c, and T_m), but has high impact on the crystallinity of these systems. The degree of crystallinity X_c significantly increases for PLA nanocomposites loaded with up to 5 wt % of TiO₂, while for 10 wt % load of TiO₂ it drops below X_c of the pure resin. The degradation of the prepared composites was evaluated hydrolytically in 1N NaOH, enzymatically in α‐amylase solutions, and under UV irradiation. The catalytic effect of TiO₂ nano particles on the degradation processes under UV light exposure (λ = 365 nm) and hydrolytic degradation was confirmed with the increase of the filler content. The opposite effect was identified in enzymatic degradation experiments. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrospun poly(L‐lactic acid)/hydroxyapatite composite fibrous scaffolds for bone tissue engineering

Poly(L ‐lactic acid) (PLLA) is one of the most studied synthetic biodegradable polymeric materials as a bone graft substitute. Taking into account the osteoconductive property of hydroxyapatite (HAp), we prepared fibrous matrices of PLLA without and with HAp particles in amounts of 0.25 or 0.50% (w/v, based on the volume of the base 15% w/v PLLA solution in 70:30 v/v dichloromethane/tetrahydrofuran). These fibrous matrices were assessed for their potential as substrates for bone cell culture. The presence of HAp in the composite fibre mats was confirmed using energy dispersive X‐ray spectroscopy mapping. The average diameters of both neat PLLA and PLLA/HAp fibres, as determined using scanning electron microscopy, ranged between 2.3 and 3.5 µm, with the average spacing between adjacent fibres ranging between 5.7 and 8.5 µm. The porosity of these fibrous membranes was high (ca 97–98%). A direct cytotoxicity evaluation with L929 mouse fibroblasts indicated that the neat PLLA fibre mats released no substance at a level that was toxic to the cells. The presence of HAp particles at 0.50% w/v in the PLLA fibrous scaffolds not only promoted the attachment and the proliferation of MC3T3‐E1 mouse pre‐osteoblastic cells, but also increased the expression of osteocalcin mRNA and the extent of mineralization after the cells had been cultured on the scaffolds for 14 and 21 days, respectively. The results obtained suggested that the PLLA/HAp fibre mats could be materials of choice for bone tissue engineering. Copyright © 2009 Society of Chemical Industry     

Structure and mechanical properties of poly(sulfone of bisphenol A)/poly(butylene terephthalate) blends

Blends of poly(sulfone of bisphenol A) (PSU) with poly(butylene terephthalate) (PBT) were obtained by direct injection moulding across the composition range. The two components of the blends reacted slightly in the melt state, producing linear copolymers. The slight changes observed in the two glass transition temperatures indicate that the copolymers were present in the two amorphous phases of the blends. The observed reactions and the high viscosity of the matrix of the PSU‐rich compositions led to a very fine morphology which could not be attained in the PBT‐rich compositions due to the low viscosity of the matrix and the direct injection moulding procedure used. This procedure is fast and economically advantageous, but leads to poor mixing. The different morphologies influenced neither the modulus nor the yield stress, which tended to follow the rule of mixtures. However, the low fracture properties of the PBT‐rich compositions contrasted with the ductility behaviour, and even the impact strength of the PSU‐rich blends, which also tended to be proportional to the blend composition. Copyright © 2004 Society of Chemical Industry     

聚乳酸/环氧大豆油共混物的性能

聚乳酸（PLA）与环氧大豆油（ESO）经熔融共混制得具有高韧性的PLA/ESO共混物,并研究了ESO含量对PLA微观形态、力学和流变性能的影响规律。结果表明：ESO可显著降低PLA的熔体黏度,提高PLA的韧性;PLA/ESO共混物在低ESO含量（10%）时为部分相容,而在高ESO含量（20%和30%）时发生了相分离,从而使共混物的断裂伸长率和冲击强度随ESO含量增加先增大后减小,且分别在ESO含量为20%和15%时达到最大值,约为PLA的17倍和2.9倍,而拉伸强度则随之减小。     

Mechanical and thermal properties of poly(lactic acid)/starch blends with dioctyl maleate

Poly(lactic acid) (PLA)/starch blends were prepared blending with dioctyl maleate (DOM). DOM acted as a compatibilizer at low concentrations (below 5%), and markedly improved tensile strength of the blend. However, DOM functioned as a plasticizer at concentrations over 5%, significantly enhancing elongation. Compatibilization and plasticization took place simultaneously according to the analysis of, for example, mechanical properties and thermal behavior. With DOM as a polymeric plasticizer, thermal loss in the blends was not significant. Water absorption of PLA/starch blends increased with DOM concentration. DOM leaching in an aqueous environment was inhibited. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1697–1704, 2004