Characterization of the mechanical and thermal properties and morphological behavior of biodegradable poly(L‐lactide)/poly(ε‐caprolactone) and poly(L‐lactide)/poly(butylene succinate‐co‐L‐lactate) polymeric blends

Two series of biodegradable polymer blends were prepared from combinations of poly(L ‐lactide) (PLLA) with poly(?‐caprolactone) (PCL) and poly(butylene succinate‐co‐L ‐lactate) (PBSL) in proportions of 100/0, 90/10, 80/20, and 70/30 (based on the weight percentage). Their mechanical properties were investigated and related to their morphologies. The thermal properties, Fourier transform infrared spectroscopy, and melt flow index analysis of the binary blends and virgin polymers were then evaluated. The addition of PCL and PBSL to PLLA reduced the tensile strength and Young's modulus, whereas the elongation at break and melt flow index increased. The stress–strain curve showed that the blending of PLLA with ductile PCL and PBSL improved the toughness and increased the thermal stability of the blended polymers. A morphological analysis of the PLLA and the PLLA blends revealed that all the PLLA/PCL and PLLA/PBSL blends were immiscible with the PCL and PBSL phases finely dispersed in the PLLA‐rich phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal decomposition behavior of γ‐irradiated poly(vinyl acetate)/poly(methyl methacrylate) miscible blends

Miscible polymer blends based on various ratios of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were prepared in film form by the solution casting technique using benzene as a common solvent. The thermal decomposition behavior of these blends and their individual homopolymers before and after γ‐irradiation at various doses (50–250 kGy) was investigated. The thermogravimetric analysis technique was utilized to determine the temperatures at which the maximum value of the rate of reaction (T_max) occurs and the kinetic parameters of the thermal decomposition. The rate of reaction curves of the individual homopolymers or their blends before or after γ‐ irradiation displayed similar trends in which the T_max corresponding to all polymers was found to exist in the same position but with different values. These findings and the visual observations of the blend solutions and the transparency of the films gave support to the complete miscibility of these blends. Three transitions were observed along the reaction rate versus temperature curves; the first was around 100–200°C with no defined T_max, which may arise from the evaporation of the solvent. The second T_max was in the 340–380°C range, which depended on the polymer blend and the γ‐irradiation condition. A third transition was seen in the rate of reaction curves only for pure PVAc and its blends with PMMA with ratios up to 50%, regardless of γ‐ irradiation. We concluded that γ‐irradiation improved the thermal stability of PVAc/PMMA blends, even though the PMMA polymer was degradable by γ irradiation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1773–1780, 2006     

Mechanical properties of poly(ε‐caprolactone) and poly(lactic acid) blends

The aim of this work was to better understand the performance of binary blends of biodegradable aliphatic polyesters to overcome some limitations of the pure polymers (e.g., brittleness, low stiffness, and low toughness). Binary blends of poly(ε‐caprolactone) (PCL) and poly(lactic acid) (PLA) were prepared by melt blending (in a twin‐screw extruder) followed by injection molding. The compositions ranged from pure biodegradable polymers to 25 wt % increments. Morphological characterization was performed with scanning electron microscopy and differential scanning calorimetry. The initial modulus, stress and strain at yield, strain at break, and impact toughness of the biodegradable polymer blends were investigated. The properties were described by models assuming different interfacial behaviors (e.g., good adhesion and no adhesion between the dissimilar materials). The results indicated that PCL behaved as a polymeric plasticizer to PLA and improved the flexibility and ductility of the blends, giving the blends higher impact toughness. The strain at break was effectively improved by the addition of PCL to PLA, and this was followed by a decrease in the stress at break. The two biodegradable polymers were proved to be immiscible but nevertheless showed some degree of adhesion between the two phases. This was also quantified by the mechanical property prediction models, which, in conjunction with material property characterization, allowed unambiguous detection of the interfacial behavior of the polymer blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Miscibility,morphology and tensile properties of vinyl chloride polymer and poly(ε‐caprolactone) blends

The miscibility, morphology and tensile properties of three blend systems of poly(ε‐caprolactone) (PCL) with poly(vinyl chloride) (PVC) and with two chlorinated PVCs (CPVCs) with different chlorine contents (63 wt% and 67 wt% of Cl) have been studied. Based on the shifts of single glass transition temperature, the Gordon–Taylor K parameter is calculated as a measurement of interaction strength between PCL and (C)PVCs. Higher K values are found for blends of (C)PVCs with higher chlorine content, together with the interaction χ parameters estimated from the melting point depression results. The morphology observed with polarized light microscopy shows that spherulites exist in blends rich in PCL (≥50 wt%) only. Wide angle X‐ray diffraction studies indicate that the crystal structure of PCL is independent of the Cl content of (C)PVCs. The tensile properties of various blends exhibit a minimum as the PCL content increases. The elongation at break increases with increasing PCL content. © 2000 Society of Chemical Industry     

Thermal stabilization of poly(3‐hydroxybutyrate) by poly(glycidyl methacrylate)

Poly(3‐hydroxybutyrate) (PHB)/poly(glycidyl methacrylate) (PGMA) blends with the PGMA content up to 30 wt % were prepared by a solution‐precipitation procedure. The thermal decomposition of PHB/PGMA blends was studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA). The thermograms of PHB/PGMA blends contained a two‐step degradation process, while that of pure PHB sample exhibited only one‐step degradation process. This degradation behavior of PHB/PGMA blends, which have a higher thermal stability as measured by maximum decomposition temperature or residual weight after isothermal degradation for 1 h, is probably due to crosslinking reactions of the epoxide groups in the PGMA component with the carboxyl chain ends of PHB fragments during the degradation process, and the occurrence of such reactions can be assigned to the exothermic peaks in their DTA thermograms. An isothermal study of these blends at 200–250°C for 1 h indicated that the residual weight was directly correlated with the amount of epoxide groups in the PHB/PGMA blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2945–2952, 2002; DOI 10.1002/app.10318     

Miscibility and crystallization behavior of biodegradable poly(ε‐caprolactone)/tannic acid blends

Miscibility, isothermal melt crystallization kinetics, spherulitic morphology and growth rates, and crystal structure of completely biodegradable poly(ε‐caprolactone) (PCL)/tannic acid (TA) blends were studied by differential scanning calorimetry, polarized optical microscopy, and wide angle X‐ray diffraction in detail in this work. PCL and TA are miscible as evidenced by the single composition dependent glass transition temperature over the whole compositions range and the depression of equilibrium melting point of PCL in the PCL/TA blends. Isothermal melt crystallization kinetics of neat PCL and an 80/20 PCL/TA blend was investigated and analyzed by the Avrami equation. The overall crystallization rates of PCL decrease with increasing crystallization temperature for both neat PCL and the PCL/TA blend; moreover, the overall crystallization rate of PCL is slower in the PCL/TA blend than in neat PCL at a given crystallization temperature. However, the crystallization mechanism of PCL does not change despite crystallization temperature and the addition of TA. The spherulitic growth rates of PCL also decrease with increasing crystallization temperature for both neat PCL and the PCL/TA blend; moreover, blending with TA reduces the spherulitic growth rate of PCL in the PCL/TA blend. It is also found that the crystal structure of PCL is not modified in the PCL/TA blend. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Use of modified poly(ϵ‐caprolactone) in the compatibilization of poly(ϵ‐caprolactone)/maize starch blends

In this work, the compatibilization of a poly(?‐caprolactone) with a number‐average molecular weight of 120,000 g/mol (PCL¹²⁰) and maize starch was investigated by the addition of a chemically modified poly(?‐caprolactone). Two types of blends were prepared by melt extrusion. In type A blends, low‐molecular‐weight compatibilizers were used: (1) a poly(?‐caprolactone) with a number‐average molecular weight of 10,000 g/mol that was reacted with maleic anhydride to obtain chains terminating in carboxylic groups and (2) low‐molecular‐weight poly(?‐caprolactone)s (number‐average molecular weights of 600 and 2000 g/mol) with one pendant carboxylic group within the chains. With these groups of blends, tensile testing and scanning electron microscopy demonstrated that the compatibilizers were generally effective in inducing a better dispersion for a 60/40 poly(?‐caprolactone)/maize starch blend with a compatibilizer, improving the mechanical properties in comparison with uncompatibilized blends. The blends with 30% starch were not improved by the addition of compatibilizer, and this may be related to the rheology of the blends during preparation. In type B blends, high‐molecular‐weight compatibilizers were prepared through the grafting of variable amounts of acrylic acid or maleic anhydride to PCL¹²⁰ chains. The best compatibilizer action was obtained with 0.7 wt % maleic anhydride grafted to PCL¹²⁰ because both the dispersion and mechanical properties were further improved in comparison with uncompatibilized blends and type A blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal properties of graphite‐loaded nitrile rubber/poly(vinyl chloride) blends

The thermal properties (thermal conductivity, thermal diffusivity, and specific heat capacity) of nitrile rubber (NBR)/poly(vinyl chloride) (PVC) blends were measured in the temperature range of 300–425 K. The incorporation of graphite into the NBR/PVC (30/70) matrix improved its thermal properties. Moreover, these properties slightly changed with the temperature. The thermal conductivity values of the prepared samples were compared with values modeled according to the Maxwell–Eucken, Cheng–Vachon, Lewis–Nielsen, geometric mean, and Agari–Uno models. The Agari–Uno model best predicted the effective thermal conductivity for the whole range of blend ratios and for the whole range of graphite contents in NBR/PVC (30/70)/graphite composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poly(vinyl pyrrolidone‐co‐vinyl acetate)‐graft‐poly(ε‐caprolactone) as a compatibilizer for cellulose acetate/poly(ε‐caprolactone) blends

Poly(vinyl pyrrolidone‐co‐vinyl acetate)‐graft‐poly(ε‐caprolactone) (PVPVAc‐g‐PCL) was synthesized by radical copolymerization of N‐vinyl‐2‐pyrrolidone (VP)/vinyl acetate (VAc) comonomer and PCL macromonomer containing a reactive 2‐hydroxyethyl methacrylate terminal. The graft copolymer was designed in order to improve the interfacial adhesiveness of an immiscible blend system composed of cellulose acetate/poly(ε‐caprolactone) (CA/PCL). Adequate selections of preparation conditions led to successful acquisition of a series of graft copolymer samples with different values of molecular weight ( ), number of grafts (n), and segmental molecular weight of PVPVAc between adjacent grafts (M_n (between grafts)). Differential scanning calorimetry measurements gave a still immiscible indication for all of the ternary blends of CA/PCL/PVPVAc‐g‐PCL (72 : 18 : 10 in weight) that were prepared by using any of the copolymer samples as a compatibilizer. However, the incorporation enabled the CA/PCL (4 : 1) blend to be easily melt‐molded to give a visually homogeneous film sheet. This compatibilizing effect was found to be drastically enhanced when PVPVAc‐g‐PCLs of higher and M_n (between grafts) and lower n were employed. Scanning electron microscopy revealed that a uniform dispersion of the respective ingredients in the ternary blends was attainable with an assurance of the mixing scale of several hundreds of nanometers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical and thermal properties of poly(butylene succinate)/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) biodegradable blends

Biodegradable polymer blends of poly(butylene succinate) (PBS) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) were prepared with different compositions. The mechanical properties of the blends were studied through tensile testing and dynamic mechanical thermal analysis. The dependence of the elastic modulus and strength data on the blend composition was modeled on the basis of the equivalent box model. The fitting parameters indicated complete immiscibility between PBS and PHBV and a moderate adhesion level between them. The immiscibility of the parent phases was also evidenced by scanning electron observation of the prepared blends. The thermal properties of the blends were studied through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC results showed an enhancement of the crystallization behavior of PBS after it was blended with PHBV, whereas the thermal stability of PBS was reduced in the blends, as shown by the TGA thermograms. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42815.     

Disclosing the crystallization behavior and morphology of poly(ϵ‐caprolactone) within poly(ϵ‐caprolactone)/poly(l‐lactide) blends

In this work, the effect of poly(l ‐lactide) (PLLA) components on the crystallization behavior and morphology of poly(?‐caprolactone) (PCL) within PCL/PLLA blends was investigated by polarized optical microscopy, DSC, SEM and AFM. Morphological results reveal that PCL forms banded spherulites in PCL/PLLA blends because the interaction between the two polymer components facilitates twisting of the PCL lamellae. Additionally, the average band spacing of PCL spherulites monotonically decreases with increasing PLLA content. With regard to the crystallization behaviors of PCL, the crystallization ability of PCL is depressed with increase of the PLLA content. However, it is interesting to observe that the growth rate of PCL spherulites is almost independent of the PLLA content while the overall isothermal crystallization rate of PCL within PCL/PLLA blends decreases first and then increases at a given crystallization temperature, indicating that the addition of PLLA components shows a weak effect on the growth rate of the PCL but mainly on the generation of nuclei. © 2018 Society of Chemical Industry     

Melt‐processed biodegradable polyester blends of poly(L‐lactic acid) and poly(ε‐caprolactone): Effects of processing conditions on biodegradation

Biodegradable polyester blends were prepared from poly(L ‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) (50/50) by melt‐blending, and the effects of processing conditions (shear rate, time, and strain) of melt‐blending on proteinase‐K‐ and lipase‐catalyzed enzymatic degradability were investigated using gravimetry, differential scanning calorimetry, and scanning electron microscopy. The proteinase‐K‐catalyzed degradation rate of the blend films increased and leveled off with increasing the shear rate, time, or strain for melt‐blending, except for the shortest shear time of 60 s. The optimal processing conditions of melt‐blending giving the maximum rate of lipase‐catalyzed degradation were 9.6 × 10² s^?1 and 180 s, whereas a deviation from these conditions caused a reduction in lipase‐catalyzed enzymatic degradation rate. At the highest shear rate of 2.2 × 10³ s^?1, PCL‐rich phase was continuous in the blend films, irrespective of the shear time (or shear strain), whereas PLLA‐rich phase changed from dispersed to continuous by increasing the shear time (or shear strain). This study revealed that the biodegradability of PLLA/PCL blend materials can be manipulated by altering the processing conditions of melt‐blending (shear rate, time, or strain) or the sizes and morphology of PLLA‐rich and PCL‐rich domains. The method reported in the present study can be utilized for controlling the biodegradability of other biodegradable polyester blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 831–841, 2007     

Evaluation of mechanical properties and physical interactions of a ternary blend of poly(ethylene‐co‐octene)/poly(ethylene‐co‐vinyl acetate)/poly(vinyl chloride) in the molten state

In this work, ethylene‐co‐vinyl acetate (EVA), poly(ethylene‐co‐octene) (POE), and poly(vinyl chloride) (PVC) blends were processed in a molten state process using a corotating twin‐screw extruder to assess both the balance of mechanical properties and physical interactions in the melt state. Tensile measurements, scanning electron microscopy, and oscillatory rheometry were performed. By means of flow curves, the parameters of the power law as well as the distribution of relaxation times were assessed with the aid of a nonlinear regularization method. The mechanical properties for the EVA‐POE blend approximated the values for POE, while inclusion of PVC shifted the modulus values to those of neat EVA. The rise in modulus was corroborated by the PVC phase dispersion as solid particles that act as a reinforcement for the ternary blend. The rheological properties in the molten state show that the POE does not present molecular entanglement effects and so tends both to diminish the EVA mechanical properties and increase the fluidity of the blend. However, the addition of PVC both restored the EVA typical pseudoplastic feature and promoted the increase in the viscosity and the mechanical properties of the ternary blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Solid‐state NMR and morphological studies of poly(ethylene‐co‐vinyl acetate)/poly(vinyl acetate) blends

To obtain a correlation among structure–morphology–mobility–compatibility properties of poly(ethylene‐co‐vinyl acetate) (EVA)/poly(vinyl acetate) (PVAc) blends, we have used scanning electron microscopy and solid‐state nuclear magnetic resonance in our investigations. The results are discussed in terms of blends, component dispersion, plasticization effect, and domain mobilities to acquire a response of the correlation between structural properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2990–2996, 1999     

Polymorphism and crystallization in poly(vinylidene fluoride)/ poly(ϵ‐caprolactone)–block–poly(dimethylsiloxane)–block–poly(ϵ‐caprolactone) blends

The miscibility, crystallization kinetics and crystalline morphology of a new system of poly(vinylidene fluoride)/poly(?‐caprolactone)‐block‐poly(dimethylsiloxane)‐block‐poly(?‐caprolactone) (PVDF/PCL‐b‐PDMS‐b‐PCL) triblock copolymer were investigated by a variety of techniques. The miscibility and phase behaviour of PVDF/PCL‐b‐PDMS‐b‐PCL were studied by determination of the melting point temperature, crystallization kinetics and Fourier transform infrared (FTIR) mapping. Chemical imaging was used as a new technique to characterize the interaction of polymer blends in crystalline morphology. The results demonstrate the existence of characteristic peaks of both PVDF and PCL in the chosen crystalline area. The crystalline structures of PVDF were affected by the PCL‐b‐PDMS‐b‐PCL triblock copolymer and facilitate the formation of the β polymorph which was illustrated by FTIR analysis. The β crystal phase fraction increases significantly on increasing the composition of the PCL‐b‐PDMS‐b‐PCL triblock copolymer. In addition, confined crystallization of PCL within PVDF inter‐lamellar and/or inter‐fibrillar regions was confirmed through polarizing optical microscopy, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering analysis. © 2019 Society of Chemical Industry     

Thermal and mechanical behaviors of poly(vinyl alcohol)–lactose blends

Thermal and mechanical behaviors of poly(vinyl alcohol) (PVA)–lactose blends were studied by differential scanning calorimetry, thermal gravimetric analysis, and stress–strain analysis. The increase in glass transition temperature of the PVA–lactose blends with lactose contents suggests the formation of hydrogen‐bonded PVA–lactose complex in the PVA matrix. The hydrogen bonding interactions can improve thermal and mechanical properties of the blends. Results of this study demonstrate that lactose, a byproduct of dairy industry, can be used directly and in substantial quantity (33%) as a modifier to enforce the physical properties of PVA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 929–935, 2002     

Porous biodegradable polyester blends of poly(L‐lactic acid) and poly(ε‐caprolactone): physical properties,morphology, and biodegradation

Poly(L ‐lactic acid) (PLLA), poly(ε‐caprolactone) (PCL), and their films without or blended with 50 wt% poly(ethylene glycol) (PEG) were prepared by solution casting. Porous films were obtained by water‐extraction of PEG from solution‐cast phase‐separated PLLA‐blend‐PCL‐blend‐PEG films. The effects of PLLA/PCL ratio on the morphology of the porous films and the effects of PLLA/PCL ratio and pores on the physical properties and biodegradability of the films were investigated. The pore size of the blend films decreased with increasing PLLA/PCL ratio. Polymer blending and pore formation gave biodegradable PLLA‐blend‐PCL materials with a wide variety of tensile properties with Young's modulus in the range of 0.07–1.4 GPa and elongation at break in the range 3–380%. Pore formation markedly increased the PLLA crystallinity of porous films, except for low PLLA/PCL ratio. Polymer blending as well as pore formation enhanced the enzymatic degradation of biodegradable polyester blends. Copyright © 2006 Society of Chemical Industry     

Novel biodegradable amphiphilic poly(ε‐caprolactone)/poly(N‐vinylpyrrolidone) blends via successive in situ polymerizations

In this study, biodegradable blends of poly(ε‐caprolactone) (PCL) and poly(N‐vinylpyrrolidone) (PVP) were prepared by a new strategy in the following steps: (1) free radical polymerization of N‐vinyl‐2‐pyrrolidone (NVP) in ε‐caprolactone (CL); (2) ring‐opening polymerization of ε‐caprolactone in the presence of PVP to obtain the target blends. The structure of the blends was confirmed by FTIR and ¹H NMR, and the molecular weight of PCL and PVP were determined by GPC. SEM study revealed that this polymerization method could decrease the disperse phase size and improve the interphase when compared with solution‐blending method. The phase inversion occurred when PVP content was 15–20 wt %. Subsequently, the PCL sphere dispersed in PVP matrix and its size decreased with the increase of PVP content. The contact angle results showed that PVP has a profound effect on hydrophilic properties of PCL/PVP blends. PCL/PVP blends are believed to be promising for drug delivery, cell therapy, and other biomedical applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure and mechanical properties of blends of poly(ε‐caprolactone) with a poly(amino ether)

Poly(ε‐caprolactone) (PCL)/poly(amino ether) (PAE) blends were obtained by injection molding without any previous extrusion step in an attempt to (i) contribute to the knowledge of the relation between structure and mechanical properties in these type of blends composed of a rubbery and a glassy polymer and (ii) to find out to which extent are the PCL/PAE blends compatible, and therefore whether the biodegradability of PCL can be added as a characteristic of PAE‐based applications. PCL/PAE blends are composed of a crystalline PCL phase, a pure amorphous PCL phase, and a PAE‐rich phase where some PCL is present. The presence of some dissolved and probably unreacted PCL in the PAE‐rich phase led to a low interfacial tension as observed by the small size of the dispersed particles and the large interfacial area. The dependence on composition of both the modulus of elasticity and the yield stress of the blends was parallel to that of the orientation level. The elongation at break showed values similar to those of PAE in PAE‐rich blends, and was slightly synergistic in very rich PCL compositions; this behavior reflects a change in the nature of the matrix, from glassy to rubbery. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008