In vitro degradation of dry‐jet‐wet spun poly(lactic acid) monofilament and knitted scaffold

In vitro degradation behavior of dry‐jet‐wet spun poly(lactic acid) (PLA) monofilament and knitted scaffold were studied at three different pH i.e., at 4.6, 7.4, and 8.0 at 37°C for 20 weeks. Characterization of PLA by intrinsic viscosity, thermal properties, and scanning electron microscopy (SEM) was carried out. It is observed that the pH of the medium has significant role on degradation behavior of PLA. The degradation at pH 4.6 is observed to be maximum, which is confirmed by the drop of 52% in intrinsic viscosity. The degradation process has effect on the hydrophobicity of the PLA. The decrease in contact angle from 73° to 48° indicates that the PLA surface tends to become more hydrophilic as the degradation proceeds. The SEM analysis showed that with the degradation, surface deterioration takes place. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2006–2012, 2007     

Compatible and crystallization properties of poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) blends

Differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD) and dynamic mechanical analysis (DMA) properties of poly(lactic acid)/ poly(butylene adipate‐co‐terephthalate) (PLA/PBAT) specimens suggest that only small amounts of poor PLA and/or PBAT crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature and onset re‐crystallization temperature values of PLA/PBAT specimens reduce gradually as their PBAT contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA analysis reduce to the minimum value as the PBAT contents of PLA_xPBAT_y specimens reach 2.5 wt %. Further morphological and DMA analysis of PLA/PBAT specimens reveal that PBAT molecules are miscible with PLA molecules at PBAT contents equal to or less than 2.5 wt %, since no distinguished phase‐separated PBAT droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/PBAT specimens, respectively. In contrast to PLA, the PBAT specimen exhibits highly deformable properties. After blending proper amounts of PBAT in PLA, the inherent brittle deformation behavior of PLA was successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tensile properties of PLA/PBAT specimens are proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Melt characteristics,mechanical, and thermal properties of blown film from modified blends of poly(butylene adipate‐co‐terephthalate) and poly(lactide)

Blown films from poly(butylene adipate‐co‐terephthalate) and poly(lactide) (PLA) blends were investigated. The blends were prepared in a twin‐screw extruder, in the presence of small amounts of dicumyl peroxide (DCP). The influence of DCP concentration on film blowing, rheological, mechanical, and thermal properties of the blends is reported in this article. Rheological results showed a marked increase in polymer melt strength and elasticity with the addition of DCP. As a consequence, the film homogeneity and the stability of the bubble were improved. The modified blend films, compared with the unmodified blend, showed an improvement in tensile strength and modulus with a slight loss in elongation. Fourier transform infrared and gel results revealed that chain scission and branching were more significant than crosslinking when the DCP loadings in the blends were not higher than 0.7%. A reduction in melt temperatures of PLA was observed due to difficulty in chain crystallization. The concentrations of DCP strongly affected the melting temperatures but had an insignificant effect on the decomposition behavior of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhancing the durability of poly(lactic acid) composites by nucleated modification

Biodegradable poly(lactic acid) (PLA) composites were prepared using an innovative combination of wood fiber (WF) and 1,3,2,4‐bis(3,4‐dimethylobenzylideno)sorbitol (DMDBS). DMDBS acted as an effective nucleating agent, which improved the mechanical properties and slowed down the degradation of the WF/PLA composites. The enzymatic degradation of the composites was examined by immersing in proteinase K or cellulase buffer. The presence of DMDBS resulted in a 26.7% increase of the crystallinity compared to the WF/PLA composites. The increase in crystallinity enhanced the thermal stability and tensile strength of the WF/DMDBS/PLA composites by 8.5%. The durability of the WF/DMDBS/PLA composites after nucleated modification was enhanced after enzymolysis. After nucleated modification, the surface of the WF/PLA composites showed clear cracks due to degradation, while these appeared about 2 weeks later in the case of the WF/DMDBS/PLA composites. The results revealed that the introduction of cellulase degraded WF in the composites, which increased hydrolysis or enzymolysis sites. The combination of nucleated modification and enzyme buffer gave an expanded downstream application of WF/PLA composites in packaging and agricultural materials. © 2019 Society of Chemical Industry     

Rheological and mechanical behavior of non-spherical poly(lactic acid) particles embedded poly(butylene adipate-co-terephthalate) blend

In this study, the poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate)(PBAT) blend is investigated to improve rheological and mechanical performances of PBAT based on rheological, mechanical, and thermal behavior analyses. The multi-step mixing method is developed to fabricate the blend with non-spherical morphology. In the multi-step mixing method, blends with a wide composition range (25/75–75/25) are mixed with additional PBAT at a mixing temperature between the melting temperatures of PBAT and PLA to produce the PBAT blend embedded with non-spherical PLA particles (10 wt%). The embedding of non-spherical PLA particles in PBAT increases the resistance against deformation, resulting in strain hardening behavior and an increase in the yield strength as well as the tear resistance of the PBAT. The presence of stiff PLA particles enhances the crystallization behavior of PBAT, meaning that polymer chains may interpenetrate. The findings of this study suggest that the multi-step mixing method is beneficial for embedding non-spherical PLA particles into a PBAT matrix, which in turn facilitates the maintenance of good interfacial adhesion to increase the melt strength, yield strength, and tear resistance.     

Hydrolytic and thermal degradation of polyethylene glycol compatibilized poly(lactic acid)-nanocrystalline cellulose bionanocomposites

This study investigates the effect of nanocrystalline cellulose (NCC) and polyethylene glycol (PEG) on the hydrolytic degradation behavior of poly(lactic acid) (PLA) bio-nanocomposites compared with that of neat PLA, under specific environmental condition, namely at 37°C in a pH 7.4 phosphate buffer medium for a time period up to 60 days. The water absorption, mass loss, molecular weight, and the morphologies of nanocomposites before and after degradation were explored. Thermogravimetric analysis (TGA) was used to study the thermal decomposition of the PLA/NCC/PEG nanocomposites before and after degradation. The results showed that the presence of hydrophilic NCC and PEG significantly accelerated the hydrolytic degradation of PLA, which was related to the rapid dissolution of PEG causing easy access of water molecules to the composites and initiating fast hydrolytic chain scission of PLA. The thermal degradation temperatures of the nanocomposites slightly decreased due to the poor thermal stability of NCC in comparison with that of the neat PLA. After degradation, the thermal stability of the separated PLA from nanocomposites significantly decreased because the molecular decreased during the hydrolytic process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46933.     

Biocomposite foams from poly(lactic acid) and rubber wood sawdust: Mechanical properties,cytotoxicity, and in vitro degradation

The objectives of this work were to seek a simple method for preparation of poly(lactic acid) (PLA) foams and evaluate properties of these foams for scaffold application. Using a typical blowing agent and compression molding, biocomposite foams were successfully prepared from a PLA/rubber wood sawdust (PLA/RWS) blend. Selection of RWS for the biocomposites was based on particle size. RWS particles in two size ranges were used: 212–600 μm and ≤75 μm. Alkaline and silane treatments were applied to the RWS before blending with PLA. The tensile properties, Izod impact strength, foam morphology, and thermal degradation of the biocomposite foams were evaluated. Cytotoxicity and in vitro degradation were tested to determine the potential of the biocomposite foam for use as a scaffold in tissue engineering. Silane treatment improved mechanical properties by increasing the interfacial adhesion between PLA and RWS. The density and void fraction of the foam samples had a greater effect on mechanical properties than pore size. Proliferation of MG-63 cells increased with culture time, indicating that the foam samples were not cytotoxic. Promising samples were tested for degradation in a lysozyme/phosphate-buffered saline and showed a slow rate of in vitro degradation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48259.     

Thermal degradation behavior of poly(vinyl chloride) in presence of poly(N‐acryloyl‐N′‐cyanoacetohydrazide)

The thermal degradation behavior of poly (vinyl chloride), PVC, in presence of poly(N‐acryloyl‐N′‐cyanoacetohydrazide), PACAH, has been studied using continuous potentiometric determination of the evolved HCl gas from the degradation process from one hand and by measuring the extent of discoloration of the degraded samples from the other. The efficiency of blending PACAH with dibasic lead carbonate, DBLC, conventional thermal stabilizer has also been investigated. A probable radical mechanism for the effect of PACAH on the thermal stabilization of PVC has been proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Improved processability and performance of biomedical devices with poly(lactic acid)/poly(ethylene glycol) blends

To improve the processability of micropolymer‐based devices used for biomedical applications, poly(lactic acid) (PLA) was melt‐blended with poly(ethylene glycol)s (PEGs) of different molecular weights (MWs; weight‐average MWs = 200, 800, 2000, and 4000; these PEGS are referred to as PEG200, PEG800, PEG2000, and PEG4000, respectively, in this article). The thermal properties, mechanical properties, and rheological properties of the PLA and the PLA–PEG blends were investigated. The tensile samples’ morphologies showed that the low‐MW PEGs filled molds well. The rheological properties confirmed that the low‐MW PEGs decreased the complex viscosity, and improved the processability. With decreasing PEG MW, the PLA glass‐transition temperature decreased. The nanoindenter data show that the addition of PEG decreased the modulus and hardness of PLA. The morphologies of the tensile samples showed that with increasing PEG MW, the thicknesses of the core layers increased gradually. The elongation at break was improved by approximately 247% with the addition of PEG200. Such methods can produce easily processed biological materials for producing biomedical products. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45194.     

Investigation on the environmental-friendly poly(lactic acid) composites based on precipitated barium sulfate: Mechanical,thermal properties,and kinetic study of thermal degradation

A novel environmental-friendly poly(lactic acid) (PLA) composites based on precipitated barium sulfate (BaSO₄) were prepared via melt-compounding. The mechanical properties and thermal stability of PLA/BaSO₄ composites were investigated. To dig the decomposition mechanism, kinetic analysis of thermal degradation was emphasized systematically based on nonisothermal thermograms. Results showed that the mechanical responses were improved remarkably both under the quasi-static condition and subjected to high-speed shock due to the well-bonded interfaces between PLA and BaSO₄. Meanwhile, the added BaSO₄ suppressed the mass conversion rate of PLA phase and improved the thermal stability at high temperature. Due to the inhibition of BaSO₄, the calculated activation energy was enhanced obviously according to model-free isoconversional approaches. Finally, the apparent kinetic mechanism and reaction order for the over-all thermal degradation were determined by the combination of model-fitting approaches and Carrasco method. From this study, we hope to provide a facile method to prepare environmental-friendly PLA composites with excellent mechanical properties and thermal stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47995.     

Thermal degradation behavior of poly(vinyl chloride) in the presence of poly(glycidyl methacrylate)

The thermal degradation behavior of poly(vinyl chloride) (PVC) in presence of poly(glycidyl methacrylate) (PGMA) has been studied using continuous potentiometric determination of the evolved HCl gas from the degradation process from one hand and by evaluating the extent of discoloration of the degraded samples from the other. The efficiency of blending PGMA with dibasic lead carbonate (DBLC) conventional thermal stabilizer has also been investigated. A probable radical mechanism for the effect of PGMA on the thermal stabilization of PVC has been suggested based on data reported by FTIR and elemental analyses. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

Thermal properties and non‐isothermal crystallization behavior of poly(trimethylene terephthalate)/poly(lactic acid) blends

Thermal properties and non‐isothermal melt‐crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(lactic acid) (PLA) blends were investigated using differential scanning calorimetry and thermogravimetric analysis. The blends exhibit single and composition‐dependent glass transition temperature, cold crystallization temperature (T_cc) and melt crystallization peak temperature (T_mc) over the entire composition range, implying miscibility between the PLA and PTT components. The T_cc values of PTT/PLA blends increase, while the T_mc values decrease with increasing PLA content, suggesting that the cold crystallization and melt crystallization of PTT are retarded by the addition of PLA. The modified Avrami model is satisfactory in describing the non‐isothermal melt crystallization of the blends, whereas the Ozawa method is not applicable to the blends. The estimated Avrami exponent of the PTT/PLA blends ranges from 3.25 to 4.11, implying that the non‐isothermal crystallization follows a spherulitic‐like crystal growth combined with a complicated growth form. The PTT/PLA blends generally exhibit inferior crystallization rate and superior activation energy compared to pure PTT at the same cooling rate. The greater the PLA content in the PTT/PLA blends, the lower the crystallization rate and the higher the activation energy. Moreover, the introduction of PTT into PLA leads to an increase in the thermal stability behavior of the resulting PTT/PLA blends. Copyright © 2011 Society of Chemical Industry     

Aging of poly(lactide)/poly(ethylene glycol) blends. Part 2. Poly(lactide) with high stereoregularity

Blending poly(ethylene glycol) (PEG) with poly(lactide) (PLA) decreases the T_g and improves the mechanical properties. The blends have lower modulus and increased fracture strain compared to PLA. However, the blends become increasingly rigid over time at ambient conditions. Previously, it was demonstrated that a PLA of lower stereoregularity was miscible with up to 30 wt% PEG. Aging was due to slow crystallization of PEG from the homogeneous amorphous blend. Crystallization of PEG depleted the amorphous phase of PEG and gradually increased the T_g until aging essentially ceased when T_g of the amorphous phase reached the aging temperature. In the present study, this aging mechanism was tested with a crystallizable PLA of higher stereoregularity. Changes in thermal transitions, solid state structure, and mechanical properties were examined over time. Blends with up to 20 wt% PEG were miscible. Blends with 30 wt% PEG could be quenched from the melt to the homogenous amorphous glass. However, this composition phase separated at ambient temperature with little or no crystallization. Changes in mechanical properties during phase separation reflected increasing rigidity of the continuous PLA-rich phase as it became richer in PLA. Construction of a phase diagram for blends of higher stereoregular PLA with PEG was attempted.     

Synergistic effects of polyethylene glycol and organic montmorillonite on the plasticization and enhancement of poly(lactic acid)

Poly(lactic acid) (PLA)/polyethylene glycol (PEG)/organic montmorillonite (OMMT) composites were prepared by melt blending, and their mechanical, rheological behavior, crystalline behavior, and thermal stability were investigated. Results showed that the elongation-at-break and notch-impact strength of PLA/15PEG/1.5OMMT were 466.45% and 4.34 kJ m⁻², respectively, which were nearly 42 and 2 times higher than those of PLA, respectively. The elongation-at-break of PLA/15PEG/1.5OMMT was also 33 times higher than that of PLA/15PEG and 30 times that of PLA/1.5OMMT. With addition of PEG, PLA chains could insert to OMMT effectively and increase the layer space of OMMT. The characteristics of dynamic behavior and fracture morphology showed that the plasticizer PEG could soften the PLA matrix, leading to easy plastic deformation. OMMT was well distributed in the PLA matrix and able to transfer the stress of external forces, thereby contributing to the matrix yielding initiation and expansion of polymer composites. The synergistic effect of OMMT and PEG was determined by studying the mechanical properties of PLA/PEG/OMMT composite. Differential scanning calorimetry and thermogravimetry studies revealed that OMMT as a nucleating agent improved crystallization and thermal stability. Thus, the synergistic effect of OMMT and PEG balanced the stiffness and toughness of PLA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47576.     

Synthesis and characterization of poly(methylene disulfide) and poly(ethylene disulfide) polymers in the presence of a phase transfer catalyst

Poly(methylene disulfide) and poly(ethylene disulfide) were synthesized from the polycondensation of methylene dichloride and ethylene dichloride monomers, respectively, in the presence of benzyltriethylammonium chloride as a phase transfer catalyst. The structures of the synthesized polysulfides were confirmed via the elemental analysis, attenuated total reflectance Fourier transform infrared spectroscopy and X-ray diffraction techniques. Moreover, the thermal behaviors of synthesized poly(methylene disulfide) and poly(ethylene disulfide) were characterized using differential scanning calorimetry and thermogravimetric analysis methods. The synthesized poly(methylene disulfide) and poly(ethylene disulfide) have molecular weights of about 2262 and 2863 g/mol, respectively. In addition, the polymers have crystalline structures absorbed in the amorphous sections. However, the d-spacing of polymers’ crystalline parts was different. Moreover, poly(methylene disulfide) and poly(ethylene disulfide) have a two- and one-step degradation behavior, respectively.     

PLA/PBAT共混物的降解性能研究

通过双螺杆挤出机和吹膜机组制备不同比例的聚乳酸/聚对苯二甲酸己二酸丁二酯（PLA/PBAT）共混物薄膜,测量共混物的热性能、力学性能,并观察其相形貌,计算共混物在堆肥条件下的生物降解率,研究共混物降解前后的结构、热力学行为和元素的变化。结果表明,PLA与PBAT是不相容体系,加入PBAT后PLA的韧性得到改善;PLA的生物降解率高于PBAT,共混物的生物降解率随着PBAT含量的增加而降低,且在降解初期,PLA的降解产物会促进PBAT的水解;PLA、PBAT及其共混物在堆肥降解前期只是大分子链水解为小分子链的过程,不发生分子链的结构变化;PLA及PBAT的降解会先发生在无定形区,共混物中PLA在无定形区的降解速度受到PBAT的影响而变慢,且共混物中PLA、PBAT的降解行为发生变化,无定形区与结晶区的降解同时发生;共混物在堆肥试验初期的降解以水解为主。     

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     

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     

Enhanced (thermo)mechanical properties in biobased poly(l-lactide)/poly(amide-12) blends using high shear extrusion processing without compatibilizers

Compatible and partly-biobased poly(l -lactide) (PLA)/polyamide-12 (PA12) blends (30 wt% PA12) are here processed by twin-screw extrusion at high shear without added compatibilizers and the effect of several processing parameters (screw speed, feed rate) on final properties (tensile strength, ductility, impact toughness, thermal resistance) is addressed. High tensile strengths could be maintained for these blends with a maximal ductility (225%) and impact toughness (48 kJ/m²) achieved for an optimal screw speed of 800 rpm. However, extreme screw speeds higher than 800 rpm dramatically reduce ductility and impact toughness. Concerning thermal resistance, a constant increase of the heat deflection temperature is observed with the screw speed and thermal resistance up to 123°C could be obtained. In this respect, processing conditions of PLA/PA12 blends have profound positive effects on all (thermo)mechanical properties. Blend morphologies were revealed by scanning electron microscopy and refined PA12 fibrils are detected at optimal processing conditions. Properties deterioration were correlated to a PA12 fibrillar-to-ellipsoidal shape transition at extreme screw speeds arising from PLA degradation and attesting for the importance of the PA12 fibrillation process on final properties. Consequently, PLA/PA12 blends represent interesting biobased candidates for high-performance applications and their optimization could be easily performed by playing with extrusion conditions without compatibilizers.