A study of morphological,thermal, rheological and barrier properties of Poly(3-hydroxybutyrate-Co-3-Hydroxyvalerate)/polylactide blends prepared by melt mixing

The paper aims to study blend properties of biodegradable polymers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactide (PLA) prepared by melt mixing. Blend compositions based on PHBV/PLA were investigated according to the following weight ratios, i.e. 100/0, 75/25, 50/50, 25/75 and 0/100 wt%. The study showed through scanning electron microscopy (SEM) that blends of PHBV/PLA are not miscible. This is consistent with differential scanning calorimetry (DSC) data which indicate the presence of two distinct glass transition temperatures (T_g) and melting temperatures (T_m), attributed to the neat polymers, over all the range of blend compositions. Water and oxygen barrier properties of PHBV/PLA blends are significantly improved with increasing the PHBV content in the blend. Further, morphological analyzes indicated that increasing the PHBV content in the polymer blends results in increasing the PLA crystallinity due to the finely dispersed PHBV crystals acting as a filler and a nucleating agent for PLA. On the other hand, the addition of PLA to the blend results in a very impressive increase in the complex viscosity of PHBV. Moreover, the rheological data showed that, excluding the specific behavior of the neat polymers at low frequencies, i.e. less than 0.1 Hz, the complex viscosity of PHBV/PLA blends fits the mixing law well.     

Compatibilized poly(ϵ‐caprolactone)/poly(L‐lactide) blends for biomedical uses

A binary poly(L ‐lactide)/poly(ε‐caprolactone) (PLLA/PCL) (70/30 w/w) blend and a ternary PLLA/PCL/PLLA‐PCL‐PLLA blend of the same composition which contains 4 wt.‐% of a triblock PLLA‐PCL‐PLLA copolyester as compatibilizing agent were prepared by melt mixing at 200°C. Investigation of the thermal and mechanical properties of the blends and scanning electron microscopy of their fracture surfaces showed in the case of the ternary blend a better state of dispersion of PCL in the PLLA matrix and an improved toughness.     

Preparation and properties of poly(lactic acid)/cellulolytic enzyme lignin/PGMA ternary blends

Poly(lactic acid)-based ternary blends consisting of poly(lactic acid)(PLA),cellulolytic enzyme lignin(CEL),and polyolefine grafting maleic anhydride(PGMA) were prepared by extrusion blending and the mechanical properties and the morphology of the ternary blends were investigated.It was found that the mechanical properties varied with various loading of the components in the blends.Compared to neat PLA,the tensile strength and the Young’s modulus of the ternary blends were decreased,but the elongation at break and the impact strength were effectively improved.Scanning electron microscope observations revealed that the CEL plays a bridging role between PLA and PGMA,enhancing the miscibility between them and resulting in the improvement of ductility and toughness of the ternary blends.Considering the cost and performance,we obtained the optimal blend PLA/CEL/ PGMA(80/20/20,w/w/w),of which the impact strength and the elongation at break were doubled as that of neat PLA,and the tensile strength remained moderate.     

聚丁二酸丁二醇酯与氯醚弹性体协同增韧改性聚乳酸多元共混体系

以来源于可再生资源聚丁二酸丁二醇酯(PBS)和氯醚橡胶(ECO)作为聚乳酸(PLA)的增韧改性剂,通过熔融共混的方法制备了PLA/PBS/ECO三元共混体系。动态力学分析和扫描电子显微镜结果表明,ECO促进了PBS和PLA之间的相容性。力学性能测试表明,ECO与PBS可实现对聚乳酸基体的协同增韧: PLA/PBS/ECO(70/20/10)显示出最优的拉伸性能,断裂伸长率高达270%;PLA/PBS/ECO(70/10/20)的冲击强度提高至23.7 kJ/m²,是纯聚乳酸的12倍。结合形态结构和冲击断面形貌分析表明ECO的存在可起到增容/增韧双重作用, 与柔性PBS产生良好的协同效应,有效改善聚乳酸材料的韧性。我们的研究表明,构造PLA-柔性生物聚酯和生物基弹性体多元共混体系是一种获得高性能生物基材料简单高效的手段。     

Miscibility and hydrolytic degradation in alkaline solution of poly(l-lactide) and poly(p-vinyl phenol) blends

Poly(l-lactide) (PLLA) was melt-blended with poly(p-vinyl phenol) (PVPh) using a two-roll mill, and the miscibility between PLLA and PVPh and degradation of the blend films were investigated. It was found that PLLA/PVPh blend has miscibility in the amorphous state because only single T_g was observed in the DSC and DMA measurements. The T_g of the PLLA/PVPh blend could be controlled in the temperature range from 55 °C to 117 °C by changing the PVPh weight fraction. In alkaline solution, degradation rate of PLLA/PVPh blends was faster than that of neat PLLA because PVPh could dissolve in alkaline solution. The surface morphology of degraded PLLA and PLLA/PVPh blend were observed by SEM. The surface morphology of degraded PLLA/PVPh blend was finer than that of PLLA. Young's modulus of PLLA/PVPh blend increased with increasing PVPh content. Yield stress of PLLA/PVPh blends whose PVPh content was less than 30 wt% kept the level of about 55 MPa and that of PLLA/PVPh blend whose PVPh content was 40 wt% is much lower than that of neat PLLA.     

Thermal and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) plasticized by biodegradable soybean oils

The effects of soybean oil (SO) and epoxidized soybean oil(ESO) as biodegradable plasticizers for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied using thermal and mechanical analyses. PHBV/SO and PHBV/ESO blends were prepared by evaporating solvent from blend solutions. The levels of additive in the blend varied from 5% to 30%. As a plasticizer for PHBV, ESO was more effective than SO in depression of the glass transition temperature as well as in increasing the elongation at break and the impact strength of the films with increasing levels of additive. Biodegradation of the plasticized PHBV films was carried out by accelerated compost method. The degradation rates of the blend films with SO or ESO were found to be faster than that of PHBV film. From the thermogravimetric analysis, it was found that the thermal reaction between the epoxide groups of ESO and PHBV fragments with carboxylic chain ends, occurred during the degradation of PHBV/ESO blends.     

Computer simulation studies of the miscibility of poly(3-hydroxybutyrate)-based blends

By means of the molecular dynamics simulation method, the miscibility of poly(3-hydroxybutyrate)/polyethylene (PHB/PE) blend has been investigated. Two glass transition temperatures of the PHB/PE are found by scrutinizing its volume-temperature curve, and this result is qualitatively in agreement with the experimental results. To further analyze the miscibility of poly(3-hydroxybutyrate)-based blends, the Flory-Huggins parameters of PHB/PE, poly(3-hydroxybutyrate)/poly(ethylene oxide) (PHB/PEO), poly(ethylene oxide)/polyethylene (PEO/PE) have been calculated via a Monte Carlo scheme, and the morphology of the PHB/PEO and the PHB/PE blend has been simulated using dissipative particle dynamics method. The time evolution of dividing interface for PHB/PEO/PE blend shows a dynamic phase separation process. All these results indicate that PHB and PEO tend to mix together, whereas PE aggregates to form PE-rich domains in the PHB/PE and PHB/PEO/PE blends.     

Effects of amorphous poly(vinyl acetate) on crystalline morphology of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)

The amorphous and crystalline phase behavior, spherulite morphology, and interactions between amorphous poly(vinyl acetate) (PVAc) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) were examined using differential scanning calorimetry, polarized-light optical and scanning electron, atomic-force microscopy (DSC, POM, SEM, AFM), and small-angle X-ray scattering (SAXS). The PHBV/PVAc blend was found to be miscible with an almost linear T _g-composition relationship, indicating perfect homogeneity. Interaction parameter by melting point depression is a negative value of χ = −0.32, suggesting quite favorable interaction strength. With the intimate interaction between the amorphous PVAc and crystalline PHBV polymers, effects of PVAc on the spherulitic morphology of PHBV are quite significant. Owing to the higher T _g of PVAc (than that of PHBV), the spherulite growth rate of PHBV was depressed by increasing PVAc content in blends. Neat PHBV exhibits ring-banded spherulites when crystallized at T_c = 60 ~ 110^° C {T_{\rm{c}}} = {6}0\sim {11}0^\circ {\hbox{C}} ; however, with increasing PVAc content in the blends, the temperature range at which the PHBV/PVAc blends exhibit ring-banded spherulites remains similar but the regularity increases, and the inter-ring spacing significantly decreases. In addition, the spherulite size and ring-band patterns therein are strongly dependent on T _max (190 vs. 220 °C, respectively, for erasing prior nuclei), from which the blends were quenched to a T _c (60–110 °C) for crystallization. For PHBV/PVAc blends crystallized at the same T _c from different T _max, higher T _max tends to erase nuclei, leading to larger spherulites. However, such larger spherulites owing to higher T _max are not necessarily packed with thicker lamellae.     

Crystallization behavior and thermal properties of blends of poly(3-hydroxybutyate-co-3-valerate) and poly(1,2-propandiolcarbonate)

Crystallization behavior of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(1,2-propandiolcarbonate) (PR(CO₂)) has been investigated by polarized light microscopy (PLM). The spherulite growth rates (SGR) of all blends were faster than that of pure PHBV, and the spherulite growth rates of PHBV in the PHBV/PR(CO₂) blends reduced with increasing PR(CO₂) weight fraction. There are two melting peaks in both the pure PHBV and the PHBV/PR(CO₂) blends. The melting peak of PHBV/PR(CO₂) blends was reduced by lower temperature about 20K as compared to PHBV and the higher temperature melting peak was increased by about 10K in the blends.     

New high impact polystyrene: Use of poly(1‐hexene) and poly(1‐hexene‐co‐hexadiene) as impact modifiers

In this study, polystyrene (PS) was melt blended with different amounts of poly1‐hexene (PH) and poly(1‐hexene‐co‐hexadiene) (COPOLY) and the blends were compared with conventional PS/polybutadiene (PS/PB) one. Scanning electron microscope revealed that the dispersion of PH and COPOLY in PS matrix was more uniform with the appearance of small particles in PS matrix; however, in the case of PS/PB blends, the fracture surface showed nonhomogenous morphology with the appearance of bigger rubber particles. Based on Differential Scanning Calorimetry (DSC) and dynamic mechanical thermal analysis results, T_g of the blends decreased in comparison with it in neat PS. Impact strength of PS/PH and PS/COPOLY blends was considerably higher than that in PS/PB and significantly higher than the value for neat PS. Tensile test showed substantial improvement in stress at yield and better elongation at break for COPOLY containing blend than the samples containing PH and PB rubbers. Also, blending of PS with 10% of the rubbers was considered in the presence of dicumylperoxide as a probable grafting/cross‐linking agent to produce XPS/COPOLY10 and XPS/PB10 samples, respectively. IR results of the nonsoluble solvent extracted gel showed that COPOLY and PB were grafted to PS matrix during melt blending, which caused higher impact strength in the related samples.     

Crystallization behavior and hydrophilicity of poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA)/poly(styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile) (SAN) ternary blends

Compatibilization of the partially miscible poly(vinylidene fluoride) (PVDF)/poly(styrene-co-acrylonitrile) (SAN) pair by a third homopolymer, i.e., poly(methyl methacrylate) (PMMA), was investigated in relation to cross section morphology, crystallization behaviors and hydrophilicity of the polyblends. Scanning electron microscopy showed a more regular and homogeneous morphology when more than 15 wt.% PMMA was incorporated. The samples presented only α phase regardless of PMMA content in the blend. As the PMMA content increased in the blends, the interactions between each component were enhanced, and the crystallization of PVDF was limited, leading to a decreasing of the crystallinity and the crystallite thickness. Besides, the hydrophilicity of PVDF was further improved by PMMA addition. The sample containing 15 wt.% PMMA showed a more hydrophilic property due to the more polar part of surface tension induced by PMMA addition. Observed from the cross section of the blends, the miscibility of partially miscible PVDF/SAN blends were efficiently improved by PMMA incorporation.     

Miscibility of poly(ϵ-caprolactone) and of poly(styrene-co-acrylonitrile) with poly(styrene-co-acrylic acid)

The miscibility of poly (?-caprolactone) (PCL) with poly (styrene-co-acrylic acid) (SAA) and of poly (styrene-co-acrylonitrile) (SAN) with SAA was examined as a function of the comonomer composition in the copolymers. For PCL/SAA blends it was found that PCL is miscible with SAA within a specific range of copolymer compositions. Segmental interaction energy densities were evaluated by analysis of the equilibrium melting point depression and application of a binary interaction model. The results suggest that the intramolecular repulsion in SAA copolymer plays an important role in inducing the miscibility. Additionally, the critical AA content in SAA for the blend to be homogeneous was predicted by correlating the segmental interaction energy densities with the binary interaction model. For SAN/SAA blends, it was also found that SAA is miscible with SAN within a specific range of copolymer compositions. From the binary interaction model, segmental interaction energy denisties between different monomer units were estimated from the miscibility map and were found to be positive for all pairs, indicating that the miscibility of the blends is due to the strong repulsion in the SAA copolymers.     

Thermal properties and degradability of poly(propylene carbonate)/poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PPC/PHBV) blends

Poly(propylene carbonate)/poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PPC/PHBV) blends were prepared via the solution casting method at different proportions. Their thermal characteristics were studied by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The degradability of the blends was investigated in soil suspension cultivation and in vitro degradation testing. The changes of structure and molecular weight for blends were also studied by ¹H nuclear magnetic resonance spectroscopy (¹H NMR), scanning electron microscopy (SEM) and gel permeation chromatography (GPC) before and after degradation. Although the PPC/PHBV blends were immiscible, the addition of PHBV could improve the thermal stability of PPC. PHBV was degraded mainly by the action of microbial enzymes in the soil suspension, which biodegraded it more rapidly than PPC in a natural environment. PPC was degraded mainly by chemical hydrolysis and random hydrolytic scission of chains in the PBS solution in vitro, and degradation of PPC was more rapid than that of PHBV in a simulated physiological environment.     

The assessment of miscibility and morphology of poly(ε-caprolactone) and poly(para-chlorostyrene) blends

The miscibility and morphology of poly(ε-caprolactone) (PCl) and poly(para-chlorostyrene) (PpClS) blend were investigated by using thermal analysis, morphological analysis, viscometry, and the study of melting point depression. A single glass transition temperature was observed by differential scanning calorimetry (DSC) for PCl/PpClS blends in the whole compositional range (0/100, 25/75, 50/50, 62.5/37.5, 75/25, 90/10). Morphology of the polymers and their blends was studied by scanning electron microscopy (SEM). The Fourier transform infrared spectra of the samples were obtained by spectrometer. Up to 12 cm⁻¹ shifts in carbonyl stretching band of PCl was detected in the spectra of PpClS rich blends. The viscosity of PCl, PpClS and their blends has also been studied to investigate the miscibility according the miscibility criteria Δb, and Δ[η]. Using this data, the interaction parameters α and μ, based on the Chee and Sun et al. approaches were determined. These criteria indicated that the blend is miscible in all proportions up to 90% of PCl content in the blends. The melting point depression of PCl in the blends was examined to obtain the interaction parameter, χ₁₂ for this system. The parameter, χ₁₂ was found to be composition dependent. Negative values of the obtained interaction parameter also support the miscibility of this system up to the 90% PCl in the blend.     

Studies of photooxidative degradation of poly(vinyl chloride)/poly(ethylene oxide) blends

The photooxidative degradation of blends (in a full range of compositions) of amorphous poly(vinyl chloride) (PVC) with semicrystalline poly(ethylene oxide) (PEO) in the form of thin films is investigated using absorption spectroscopy (UV–visible and Fourier transform infrared) and atomic force microscopy (AFM). The amount of insoluble gel formed as a result of photocrosslinking is estimated gravimetrically. It is found that the PVC/PEO blendsí susceptibility to photooxidative degradation differs from that pure of the components and depends on the blend composition and morphology. Photoreactions such as degradation and oxidation are accelerated whereas dehydrochlorination is retarded in blends. The photocrosslinking efficiency in PVC/PEO blends is higher than in PVC; moreover, PEO is also involved in this process. AFM images showing the lamellar structure of semicrystalline PEO in the blend lead to the conclusion that the presence of PVC does not disturb the crystallization process of PEO. The changes induced by UV irradiation allow the observation of more of the distinct PEO crystallites. This is probably caused by recrystallization of short, more mobile chains in degraded PEO or by partial removal of the less stable amorphous phase from the film surface. These results confirm previous information on the miscibility of PVC with PEO. The mechanism of the interactions between the components and the blend photodegradation are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 585–602, 2004     

Molecular dynamics and phase behavior of polystyrene/poly(vinyl methyl ether) blend in the presence of nanosilica

The variation of phase morphology, critical temperature of demixing, and molecular dynamics for polystyrene/poly(vinyl methyl ether)(PS/PVME) blends induced by hydrophilic nanosilica(A200) or hydrophobic nanosilica(R974) was investigated. With the phase separation of blend matrix, A200 migrated into PVME-rich phase due to strong interaction between A200 and PVME, while R974 moved into PS-rich phase. The thermodynamic miscibility and concentration fluctuation during phase separation of blend matrix were remarkably retarded by A200 nanoparticles due to the surface adsorption of PVME on A200, verified by the correlation length ξ near the critical region from rheological measurement and the weakened increment of reversing heat capacity(ΔC_p) during glass transition via modulated differential scanning calorimetry(MDSC). The restricted chain diffusion induced by nanosilica still occurred despite no influence of A200 and R974 on the segmental dynamics of homogenous blend matrix. The interactions between nanosilica and polymer components could restrict the terminal relaxation of blend matrix and further manipulate their phase behavior.     

Analysis and evaluation of biobased polyester of PTT/PBAT blend: thermal,dynamic mechanical,interfacial bonding,and morphological properties

Novel blends were prepared from biobased poly(trimethylene terephthalate) (PTT) and poly(butylene adipate‐co‐terephthalate) (PBAT) using a twin screw extrusion process as a function of different weight ratios. Thermal stability, mechanical, and interfacial properties of PTT/PBAT blends were investigated using a thermogravimetric analyzer and mechanical analyzer. Phase behavior and surface morphology of the blends were characterized using scanning electron microscopy. Interfacial bonding value of the PTT/PBAT blend was evaluated from the Pukanszky empirical relationship. Viscoelastic properties of PTT/PBAT blends were investigated using the dynamic mechanical analyzer. PTT/PBAT blend exhibited higher thermal stability than the neat PTT matrix. The entire blend showed better interfacial adhesion between the matrixes. Storage and loss modulus of the PTT/PBAT blend reduces with increasing PBAT content. PTT/PBAT blend exhibited higher impact energy than the neat PTT matrix, because of its flexible and amorphous nature of PBAT polymer and increasing toughness. Copyright © 2016 John Wiley & Sons, Ltd.     

Miscibility and transesterification in ternary blends of poly(ethylene naphthalate)/poly(trimethylene terephthalate)/poly(ether imide)

Miscibility and morphology of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate)/poly(ether imide) (PEN/PTT/PEI) blends were investigated by using a differential scanning calorimeter (DSC), optical microscopy (OM), wide-angle X-ray diffraction (WAXD), and proton nuclear magnetic resonance (¹H-NMR). In the ternary blends, OM and DSC results indicated immiscible properties for polyester-rich compositions of PEN/PTT/PEI blends, but all compositions of the ternary blends were phase homogeneous after heat treatment at 300 °C for more than 30 min. An amorphous blend with a single T _g was obtained in the final state, when samples were annealed at 300 °C. Experimental results from ¹H-NMR identified the production of PEN/PTT copolymers by so-called “transesterification”. The influence of transesterification on the behaviors of glass transition and crystallization was discussed in detail. Study results identified that a random copolymer promoted the miscibility of the ternary blends. The critical block lengths for both PEN and PTT hindered the formation of crystals in the ternary blends. Finally, the transesterification product of PEN/PTT blends, ENTT, was blended with PEI. The results for DSC and OM demonstrated the miscibility of the ENTT/PEI blends.     

Superior heat-resistant polylactide/poly(butylene succinate) blend fibers via in-situ reactive compatibilization

Blending poly(butylene succinate) (PBS) with polylactide (PLLA) has proven effective in improving heat resistance of PLLA fibers. Unfortunately, it remains challenging to maintain good spinnability for PLLA/PBS blends with high content of PBS with which further improved heat resistance could be anticipated. In this study, reactive melt-extrusion was devised to in-situ generate PLLA-PBS copolymers by introducing zinc acetate as a transesterification catalyst into PLLA/PBS blends. The compatibility between the PLLA and PBS phases was greatly improved by the formation of PLLA-PBS copolymers, resulting in excellent melt-spinnability even for the PLLA/PBS blends with high PBS content up to 20 wt%. In addition, an increase in crystallinity of PLLA was achieved in PLLA/PBS blend fibers, thanks to the enhanced compatibility. More importantly, the presence of PBS nuclei retarded the molecular orientation of the amorphous PLLA phase, consistent with the effective results from the relaxation heat-setting treatment. These led to an exceptionally improved heat resistance of the PLLA/PBS blend fibers. As an encouraging result, the boiling water shrinkage was significantly reduced from ca. 20% for neat PLLA fibers to 3.7% for the PLLA/PBS blend fibers with 20 wt% PBS content. These findings may open up a facile and effective route to develop PLLA/PBS blend fibers showing sound spinnability, greatly improved heat resistance and softness.     

Improvement in Toughness of Polylactide by Melt Blending with Bio-based Poly（ester）urethane

Polylactide （PLA） was successfully toughened by blending with bio-based poly（ester）urethane （TPU） elastomers which contained bio-based polyester soft segments synthesized from biomass diols and diacids. The miscibility, mechanical properties, phase morphology and toughening mechanism of the blend were investigated. Both DSC and DMTA results manifested that the addition of TPU elastomer not only accelerated the crystallization rate, but also increased the final degree of crystallinity, which proved that TPU has limited miscibility with PLA and has functioned as a plasticizer. All the blend samples showed distinct phase separation phenomenon with sea-island structure under SEM observation and the rubber particle size in the PLA matrix increased with the increased contents of TPU. The mechanical property variation of PLA/TPU blends could be quantitatively explained by Wu＇s model. With the variation of TPU, a brittle-ductile transition has been observed for the TPU/PLA blends. When these blends were under tensile stress conditions, the TPU particles could be debonded from the PLA matrix and the blends showed a high ability to induce large area plastic deformation before break, which was important for the dissipation of the breaking energy. Such mechanism was demonstrated by tensile tests and scanning electron microcopy （SEM） observations.