Miscibility,morphology and thermal properties of poly(para‐dioxanone)/poly(D,L‐lactide) blends

BACKGROUND: Poly(para‐dioxanone) (PPDO) is a biodegradable polyester with excellent biodegradability, bioabsorbability, biocompatibility and mechanical flexibility. However, its high cost and relatively fast degradation rate have hindered the development of commercial applications. Blending with other polymers is a simple and convenient way of modifying the properties of aliphatic polyesters. Poly(D ,L ‐lactide) (PDLLA) is another polyester that has been extensively studied for biomedical applications due to its biocompatibility and suitable degradation rate. However, to our knowledge, blends of PPDO/PDLLA have not been reported in the literature. RESULTS: A series of biodegradable polymers were blended by solution co‐precipitation of PPDO and PDLLA in various blend ratios. The miscibility, morphology and thermal properties of the materials were investigated. DSC curves for all blends revealed two discrete glass transition temperatures which matched the values for pure PPDO and PDLLA. SEM images of fracture surfaces displayed evidence of phase separation consistent with the DSC results. The contact angles increased with the addition of PDLLA. CONCLUSION: PPDO/PDLLA blends exhibit two distinct glass transition temperatures that remain nearly constant and correspond to the glass transition temperatures of the homopolymers for all blend compositions, indicating that blends of PPDO and PDLLA are immiscible. Images of the surface obtained using SEM were also suggestive of a two‐phase material. The crystallinity of the PPDO phase in the blends was affected by the PDLLA content. The mechanical properties of the blends changed dramatically with composition. Adding PDLLA makes the blends less hydrophilic than PPDO. Copyright © 2008 Society of Chemical Industry     

Preparation of poly(L‐lactide) film having high elastic recovery

Triacetin (TAC) is known as a lubricant of poly(L ‐lactide) (PLLA), and it is used to improve the mechanical properties of PLLA. However, the compatibility of TAC with PLLA and the morphological changes induced by the addition of TAC to PLLA have not been clarified. This study investigates the effects of the addition of TAC on the morphological changes and physical properties of PLLA. We prepared the PLLA films containing a given amount of TAC by solvent‐cast blending with chloroform under a low temperature. From the investigation of the mechanical properties of the blends, it is found that the glass‐transition temperature of PLLA is remarkably decreased with an increasing amount of TAC, the blend films exhibit high elastic recovery, and the degree of the recovery increases linearly with the amount of TAC. The morphological changes exhibiting high elastic recovery are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 474–480, 2003     

Study of the miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) blends

The miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) (PEO/PVA) blends were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and polarizing optical microscopy. Because the glass‐transition temperature of PVA was near the melting point of PEO crystalline, an uncommon DSC procedure was used to determine the glass‐transition temperature of the PVA‐rich phase. From the DSC and DMA results, two glass‐transition temperatures, which corresponded to the PEO‐rich phase and the PVA‐rich phase, were observed. It was an important criterion to indicate that a blend was immiscible. It was also found that the preparation method of samples influenced the morphology and crystallization behaviors of PEO/PVA blends. The domain size of the disperse phase (PVA‐rich) for the solution‐cast blends was much larger than that for the coprecipitated blends. The crystallinity, spherulitic morphology, and isothermal crystallization behavior of PEO in the solution‐cast blends were similar to those of the neat PEO. On the contrary, these properties in the coprecipitated blends were different from those of the neat PEO. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1562–1568, 2004     

Enzymatic degradation of poly(D,L‐lactide) and its blends with poly(vinyl acetate)

The enzymatic degradation of poly(D ,L ‐lactide) (PLA) was investigated using two different lipases, Novozym 435 and Lipolase. The optimum temperature was 50°C for the enzymatic degradation of PLA. The effect of various solvents on the degradation of PLA was investigated at 50°C using Novozym 435, and toluene was found to be the best solvent among the solvents investigated. The enzymatic degradation of the blends of PLA and PVAc was investigated at 50°C in toluene. The enzymatic degradation of the blends of PLA and PVAc showed that there is an interaction between the polymers during degradation, which results in the reduction of degradation rate of both polymers in the blend. A continuous distribution model was used to determine the rate coefficients for polymer degradation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 657–680 2006     

Reactive blending of poly(L‐lactic acid) with poly(ethylene‐co‐vinyl alcohol)

Poly(L ‐lactic acid) (PLLA) was blended with poly(ethylene‐co‐vinyl alcohol) (EVOH) in the presence of an esterification catalyst to induce reaction between the hydroxyl groups of EVOH and the terminal carboxylic group of PLLA. Nascent low‐molecular‐weight PLLA, obtained from a direct condensation polymerization of L ‐lactic acid in bulk state, was used for the blending. Domain size of the PLLA phase in the graft copolymer was much smaller than that corresponding to a PLLA/EVOH simple blend. The mechanical properties of the graft copolymer were far superior to those of the simple blend, and the graft copolymer exhibited excellent mechanical properties even though the biodegradable fraction substantially exceeded the percolation level. The grafted PLLA reduced the crystallization rate of the EVOH moiety. Melting peak temperature (T_m) of the PLLA phase was not observed until the content of PLLA in the graft reaction medium went over 60 wt %. The modified Sturm test results demonstrated that biodegradation of EVOH‐g‐PLLA took place more slowly than that of an EVOH/PLLA simple blend, indicating that the chemically bound PLLA moiety was less susceptible to microbial attack than PLLA in the simple blend. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 886–890, 2005     

Miscibility of segmented polyurethane/poly(vinyl chloride) blends

Miscibilities of segmented polyurethanes (SPUs) and poly(vinyl chloride) (PVC) or functionalized poly(vinyl chloride) (FPVC) were studied with dynamic mechanical analysis, differential scanning calorimetry, and X‐ray diffraction. Mechanical properties of the blends were also studied with tensile measurements. The miscibility of the blends depended greatly on the hard‐segment content of SPU and the existence of the functional groups. The combination of SPU with a low hard‐segment content and PVC with functional groups made the blend system miscible. Moreover, controlling the blend composition of SPU/FPVC allowed us to modify the mechanical properties of SPU, where the elongation at break was multiplied without a significant change in its tensile strength. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3022–3029, 2001     

Physical properties and enzymatic hydrolysis of poly(L‐lactide)–TiO2 composites

Amorphous poly(L ‐lactide) (PLLA) composite films with titanium dioxide (TiO₂) particles were prepared by solution‐casting using methylene chloride as a solvent, followed by quenching from the melt. The effects of surface treatment, volume fraction, size, and crystalline type of the TiO₂ particles on the mechanical properties and enzymatic hydrolysis of the composite films were investigated. The tensile strength of the PLLA composite films containing TiO₂ particles except for anatase‐type ones with a mean particle size of 0.3–0.5 μm was lowered and the Young's modulus became higher with increasing the content of TiO₂ particles. The tensile strength of the composite films containing anatase‐type TiO₂ with a mean particle size of 0.3–0.5 μm at contents of 20 wt % or less was almost the same as that of the pure PLLA film. The enzymatic hydrolysis of PLLA matrix was accelerated by the addition of the hydrophilic anatase‐type TiO₂ particles (nontreated or Al₂O₃ treated) with a mean particle size of 0.3–0.5 μm at relatively high contents such as 20 wt %. On the other hand, the enzymatic hydrolysis of PLLA matrix was inhibited by composite formation with the hydrophobic rutile‐type TiO₂ particles (Al₂O₃‐stearic acid treated, or ZrO₂‐Al₂O₃‐stearic acid treated). These results suggest that the mechanical properties and enzymatic hydrolyzability of the PLLA can be controlled by the kind and amount of the added TiO₂ particles. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 190–199, 2005     

Characterization of degraded hydrogels based on poly(vinyl alcohol) grafted with poly(lactide‐co‐glycolide)

Poly(vinyl alcohol) (PVA) grafted with poly(lactide‐co‐glycolide) and cross‐linked as a material of increased hydrophobicity relative to PVA was produced. The properties were examined with respect to the mass loss, water uptake, hydrophilicity, and mechanical characteristics upon hydrolytical degradation. The hydrogels investigated display water uptake increasing with degradation time because of increasing hydrophilicity. The mass loss amounts up to 15% after eight weeks of degradation. The mechanical properties of the hydrogels are within the range of those of natural tissue, the E modulus is 18 MPa, or even 100–200 MPa, depending on the structure of material. The mechanical characteristic and their dependence degradation show the most recognizable correlation with the chemical structure. Studies of the topography of degraded samples (scanning electron microscopy) and IR measurements demonstrate the degradation to occur at slow rate due to the high degree of grafting. The mass loss is rather low and a bulk degradation mechanism takes place. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photocurable biodegradable polyesters from poly(L‐lactide) diols

α,ω‐Dihydoxy‐terminated poly(L ‐lactide)s (PLLA diols) with various molecular weights (1000, 2000 and 3000 g mol^?1) were prepared by the ring‐opening polymerization of L ‐lactide using 1,6‐hexanediol as an initiator. These were subsequently chain‐extended with the diacyl chloride of 4,4′‐(adipoyldioxy)dicinnamic acid (CAC) to obtain high‐molecular‐weight photocurable polyesters (CAC/PLLAs). The resulting polyesters were characterized by gel permeation chromatography, Fourier‐transform infrared, ultraviolet–visible and proton nuclear magnetic resonance spectroscopies, differential scanning calorimetry and thermogravimetry. These photoreactive polyesters were irradiated with a high‐pressure mercury lamp (λ > 280 nm) for 30–180 min to produce the crosslinked polyesters. The gel fraction yield increased with photocuring time, and exceeded 80 % after 180 min. The photocuring process disturbed the crystallization of the CAC/PLLA films, while it enhanced their thermal stabilities. With increasing photocuring time, both the tensile strength and modulus increased markedly. The best mechanical properties (tensile strength = 41 MPa; tensile modulus = 1550 MPa) were obtained for a CAC/PLLA‐3000 film photocured for 180 min. The tensile modulus of this photocured film was larger than that of pure PLLA. The hydrolytic degradation rates of the CAC/PLLA films in a phosphate buffer solution (pH, 7.2) of proteinaze‐k at 37 °C were much slower than those of pure PLLA films. Copyright © 2004 Society of Chemical Industry     

Thermal properties and non‐isothermal crystallization behavior of biodegradable poly(p‐dioxanone)/poly(vinyl alcohol) blends

Blends of two biodegradable semicrystalline polymers, poly(p‐dioxanone) (PPDO) and poly(vinyl alcohol) (PVA) were prepared with different compositions. The thermal stability, phase morphology and thermal behavior of the blends were studied by using thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). From the TGA data, it can be seen that the addition of PVA improves the thermal stability of PPDO. DSC analysis showed that the glass transition temperature (T_g) and the melting temperature (T_m) of PPDO in the blends were nearly constant and equal to the values for neat PPDO, thus suggesting that PPDO and PVA are immiscible. It was found from the SEM images that the blends were phase‐separated, which was consistent with the DSC results. Additionally, non‐isothermal crystallization under controlled cooling rates was explored, and the Ozawa theory was employed to describe the non‐isothermal crystallization kinetics. Copyright © 2006 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     

Miscibility and phase structure of binary blends of polylactide and poly(vinylpyrrolidone)

The miscibility, crystallization behavior, and component interactions of two binary blends, poly(L ‐lactide) (L ‐PLA)/poly(vinylpyrrolidone) (PVP) and poly(D ,L ‐lactide) (DL ‐PLA)/PVP, were studied with differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. The composition‐dependent changes of the glass‐transition temperature (T_g) and degree of crystallinity (X_c) of the L ‐PLA phase indicated that L ‐PLA and PVP were immiscible over the composition range investigated. However, the sharp decrease of X_c with increasing PVP content in the second heating run demonstrated that the cold crystallization process of L ‐PLA was remarkably restricted by PVP. In DL ‐PLA/PVP blends, the existence of two series of isolated T_g's indicated that DL ‐PLA and PVP were phase‐separated, but evidence showed that there was some degree of interaction at the interface of the two phase, especially for the blends with low DL ‐PLA contents. FTIR measurements showed that there was no appreciable change in the spectra of L ‐PLA/PVP with respect to the coaddition of each component spectrum, implying the immiscibility of the two polymers. In contrast to L ‐PLA, the intermolecular interaction between DL ‐PLA and PVP was detected by FTIR; this was evidenced by the observation of a high‐frequency shift of the C?O stretching vibration band of PVP with increasing DL ‐PLA content, which suggested some degree of miscibility. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 973–979, 2003     

Miscibility of biodegradable aliphatic polyester and poly(vinyl acetate) blends

We report miscibility behavior for synthetic biodegradable aliphatic polyester (BDP) and poly(vinyl acetate) (PVAc) blends by investigating their thermal, rheological, and mechanical properties. Two separate glass transition temperature peaks for the BDP/PVAc blends proved that these blend systems are immiscible. From the rheological measurement, the shear viscosity as a function of shear rate is observed to increase with increasing PVAc content in BDP/PVAc blends, since PVAc has a relatively high molecular weight compared to BDP. Moreover, BDP blends with 10 wt % PVAc have excellent mechanical properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1348–1352, 2000     

Miscibility and thermal behavior of poly(vinyl chloride)/feather keratin blends

Various poly(vinyl chloride) (PVC)/feather keratin (FK) blends were prepared via a solution blending method in the presence of N,N‐dimethylformamide as a solvent. The miscibility of the blends was studied with different analytical methods, such as dilute solution viscometry, differential scanning calorimetry, refractometry, and atomic force microscopy. According to the results obtained from these techniques, it was concluded that the PVC/FK blend was miscible in all the studied compositions. Specific interactions between carbonyl groups of the FK structure and hydrogen from the chlorine‐containing carbon of the PVC were found to be responsible for the observed miscibility on the basis of Fourier transform infrared spectroscopy. Furthermore, increasing the FK content in the blends resulted in their miscibility enhancement. The thermal stability of the samples, as an important characteristic of biobased polymer blends, was finally examined in terms of their FK weight percentage and application temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crystallization behavior and mechanical properties of bio‐based green composites based on poly(L‐lactide) and kenaf fiber

Bio‐based polymer composite was successfully fabricated from plant‐derived kenaf fiber (KF) and renewable resource‐based biodegradable polyester, poly(L ‐lactide) (PLLA), by melt‐mixing technique. The effect of the KF weight contents (0, 10, 20, and 30 wt %) on crystallization behavior, composite morphology, mechanical, and dynamic mechanical properties of PLLA/KF composites were investigated. It was found that the incorporation of KF significantly improves the crystallization rate and tensile and storage modulus. The crystallization of PLLA can be completed during the cooling process from the melt at 5°C/min with the addition of 10 wt % KF. It was also observed that the nucleation density increases dramatically and the spherulite size drops greatly in the isothermal crystallization with the presence of KF. In addition, with the incorporation of 30 wt % KF, the half times of isothermal crystallization at 120°C and 140°C were reduced to 46.5% and 28.1% of the pure PLLA, respectively. Moreover, the tensile and storage modulus of the composite are improved by 30% and 28%, respectively, by the reinforcement with 30% KF. Scanning electron microscopy observation also showed that the crystallization rate and mechanical properties could be further improved by optimizing the interfacial interaction and compatibility between the KF and PLLA matrix. Overall, it was concluded that the KF could be the potential and promising filler for PLLA to produce biodegradable composite materials, owing to its good ability to improve the mechanical properties as well as to accelerate the crystallization of PLLA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis,physical properties,and crystallization of optically active poly(L‐phenyllactic acid) and poly(L‐phenyllactic acid‐co‐L‐lactic acid)

Optically active poly(L ‐phenyllactic acid) (Ph‐PLLA), poly(L ‐lactic acid) (PLLA), and poly(L ‐phenyllactic acid‐co‐L ‐lactic acid) with weight‐average molecular weight exceeding 6 × 10³ g mol^?1 were successfully synthesized by acid catalyzed direct polycondensation of L ‐phenyllactic acid and/or L ‐lactic acid in the presence of 2.5–10 wt % of p‐toluenesulfonic acid. Their physical properties and crystallization behavior were investigated by differential scanning calorimetry, thermogravimetry, and polarimetry. The absolute value of specific optical rotation ([α]) for Ph‐PLLA (?38 deg dm^?1 g^?1 cm³) was much lower than that of [α] for PLLA (?150 deg dm^?1 g^?1 cm³), suggesting that the helical nature was reduced by incorporation of bulky phenyl group. PLLA was crystallizable during solvent evaporation, heating from room temperature, and cooling from the melt. Incorporation of a very low content of bulky phenyllactyl units even at 4 mol % suppressed the crystallization of L ‐lactyl unit sequences during heating and cooling, though the copolymers were crystallizable for L ‐phenylactyl units up to 6 mol % during solvent evaporation. The activation energy of thermal degradation (ΔE_td) for Ph‐PLLA (200 kJ mol^?1) was higher than that for PLLA (158 kJ mol^?1). The ΔE_td for the copolymers increased with an increase in L ‐phenyllactyl unit content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Binary blends based on poly(N‐isopropylacrylamide): Miscibility studies with PVA,PVP, and PAA

Blends of poly(vinyl alcohol) (PVA), poly(acrylic acid), (PAA), and poly(vinyl pyrrolidone) (PVP), with poly(N‐isopropylacrylamide) (PNIPAM), were prepared by casting from aqueous solutions. Mechanical properties of PNIPAM/PVA blends were analyzed by stress–strain tests. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were employed to analyze the miscibility between the polymeric pairs. The results revealed that PNIPAM is not miscible with PVA and PVP in the whole range of composition. On the other hand, PNIPAM interacts strongly with PAA forming interpolymer complex due to the formation of cooperative hydrogen bonds. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 743–748, 2004     

Miscibility study of polymer blends composed of semirigid thermotropic liquid crystalline polycarbonate,poly(vinyl alcohol), and chitosan

Miscibility of binary and ternary polymer blends composed of thermotropic liquid crystalline polycarbonate (LCPC), poly(vinyl alcohol) (PVA), and chitosan was investigated by viscosity method, FTIR spectrum, and scanning electron microscope techniques. Effect of addition of chitosan as a compatibilizer on miscibility and morphology of binary LCPC/chitosan and PVA/chitosan and ternary LCPC/PVA/chitosan polymer blends was discussed. These measurements indicated that addition of chitosan into the blends of LCPC with PVA leads to an increase of miscibility and a formation of clear fibril structures on fractured surfaces, which are due to intermolecular hydrogen‐bonding interaction between LCPC, PVA, and chitosan chains. It was suggested that side‐chain hydroxy group of PVA and amino and hydroxy groups of chitosan play an important role in the formation of miscible phase and improvement of morphology in binary and ternary blends composed of LCPC, PVA, and chitosan. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1616–1622, 2004     

Mixtures of poly(vinyl chloride) and copolyesters based on ε‐caprolactone and L‐lactide: Miscibility,thermal stability,and weathering resistance

Properties of the blends of Poly(vinyl chloride) (PVC) and poly(ε‐caprolactone) (PCLO) and copolyesters based on ε‐caprolactone and L‐lactide (LLA) prepared by rolling were studied. Incorporating the LLA units into the structure of PCLO the content of the crystalline phase was controlled. Miscibility of the blends was assessed using DMA, and basic mechanical properties were correlated with the type and content of the polymer plasticizer. The PVC blends containing up to 20 wt parts polyesters were miscible. The presence of the LLA units in the copolyester influenced negatively the thermal stability. On the other hand even small content of copolyester in the blend enhanced the resistivity against aging. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Part 7. Effects of poly(L‐lactide‐co‐ϵ‐caprolactone) on morphology,structure, crystallization,and physical properties of blends of poly(L‐lactide) and poly(ϵ‐caprolactone)

Blended films of poly(L ‐lactide) [ie poly(L ‐lactic acid)] (PLLA) and poly(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐caprolactone) (PLLA‐CL) were prepared by solution‐casting. The effects of PLLA‐CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA‐CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross‐section of the PLLA/PCL blend film. The melting temperatures (T_m) of PLLA and PCL in the films remained unchanged upon addition of PLLA‐CL, while the crystallinities of PLLA and PCL increased at PLLA contents [X_PLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4–0.7 and at most of the X_PLLA values, respectively. The addition of PLLA‐CL improved the tensile strength and the Young modulus of the films at X_PLLA of 0.5–0.8 and of 0–0.1 and 0.5–0.8, respectively, and the elongation at break of the films at all the X_PLLA values. These findings strongly suggest that PLLA‐CL was miscible with PLLA and PCL, and that the dissolved PLLA‐CL in PLLA‐rich and PCL‐rich phases increased the compatibility between these two phases. © 2003 Society of Chemical Industry