Poly(epsilon-caprolactone)/chitin and poly(epsilon-caprolactone)/chitosan blend films with compositional gradients: fabrication and their biodegradability

Poly(epsilon-caprolactone) (PCL)/chitin and PCL/chitosan blend films with compositional gradients were successfully fabricated by a dissolution/diffusion method; that is, repeatedly pouring the PCL/chitin (or PCL/chitosan) blend solutions, with variable composition, onto polysaccharide layers. The compositional gradient structure in the resulting films was characterized by polarized optic microscopy, ATR-FT-IR and trans-FT-IR microscopic spectroscopy. Enzymatic degradability of the PCL/chitin and PCL/chitosan blend films with compositional gradients in the presence of lysozyme was compared with those of homogeneous films and two-layer films. It was found that the degradation rate of PCL/chitin blend films with a compositional gradient was far lower than that of the neat chitin film, whereas the degradation rate of PCL/chitosan blend films with a compositional gradient was close to that of the neat chitosan film. The suppression of the chitosan crystallization, which accelerates the enzymatic degradation, at the surface of PCL/chitosan films with a compositional gradient was much more severe than that for PCL/chitin films with a compositional gradient.     

Effect of the molecular weight of poly(vinyl alcohol) on the water stability of a syndiotactic poly(vinyl alcohol)/iodine complex film

To precisely identify the effect of the molecular weight of syndiotactic poly(vinyl alcohol) (s-PVA) on the water stability of a s-PVA/iodine complex film, we prepared four s-PVAs with similar syndiotactic diad (s-diad) contents of about 63% and with different number-average degrees of polymerization, P_n, of 900, 6,000, 10,000, and 17,000, respectively. The desorption behavior of iodine in the s-PVA/iodine complex film in water was investigated in relation to the solubility of s-PVA in water. The degree of solubility of a s-PVA film having different P_n in water at 80 °C was limited to about 0.3-10%, whereas the degrees of solubility of atactic PVA films with P_n of 6,000 and 10,000 were 100% at the same conditions. The degree of iodine desorption of the complex film decreased with increasing P_n of s-PVA. Especially, the degree of iodine desorption of a PVA drawn film having P_n of 17,000 was limited to 2%, regardless of soaking temperature from 40 to 80 °C. The desorption of iodine in water was strongly affected by the dissolution of PVA. In addition, the degree of iodine desorption of the drawn s-PVA/iodine film was larger than that of the undrawn one.     

Honeycomb pattern formation via polystyrene/poly(2-vinylpyridine) phase separation

The surface morphologies and properties of polystyrene (PS)/poly(2-vinylpyridine) (PVP) blend films cast on the mica substrate from ethylbenzene solution were investigated upon controlling different weight ratios and solvent evaporation rates. A near-honeycomblike surface morphology of the PS/PVP blend film formed under controlling the solvent evaporation rate due to the effect of Marangoni-Benard convection. The results of static water contact angles, X-ray photoelectron spectroscopy, solvent selective etching, and treatment by water illustrated that the near-honeycomblike structures on the surface of PS/PVP blend films were different for different weight ratios of PS and PVP. After treatment with water for several minutes, PVP islands-like structure emerged in the holes of the film for a PS/PVP weight ratio of 4/1, and a quasihexagonal arrangement of alternate big and small PVP droplets emerged on the top layer of the film for a PS/PVP weight ratio of 7/1. The formation mechanisms of different surface structures and their response behaviors to water were discussed.     

Self‐organization of functional gradient structure in the biodegradable chitosan/poly(vinyl alcohol) blend film

Biologically inspired optimal structures combining the bioresorbable and bioactive properties are expected for the next generation of biomaterials. A compositional gradient structure was found to be spontaneously formed in the film of biodegradable chitosan/poly(vinyl alcohol) blend by casting aqueous solution on an aluminum dish. The formation of compositional gradient structure was confirmed by FTIR mapping measurement, DMTA measurement, and SEM observation on the freeze‐fractured cross section. In DMTA measurement, a broadening of the α‐relaxation curve corresponding to the glass transition was observed for the compositional gradient film, while a composition‐dependent single glass transition was observed for the homogeneous blend films. The resulted film with stable self‐organized compositional gradient exhibits novel physical properties inaccessible for the film of homogeneous blends obtained by casting from the same solution on a Teflon dish. The compositional gradient films present a unique combination of stronger stress and higher yield strain when compared with those of the homogeneous films at both dry and wet states. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3069–3076, 2005     

Micro construction of poly(epsilon-caprolactone)/poly(L-lactic acid) blend film by solution casting under microwave irradiation

The micro construction of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) blend films fabricated by solution casting under microwave irradiation was investigated by selective enzymatic degradation and scanning electron microscopy (SEM). The results were totally different from the blends obtained by conventional methods. The blend was more homogeneous and the PCL continuous phase more compact as no spherulites and tiny zone separation were observed from the film surface and no PCL network was observed inside the film, and the degradation of a PCL plank by Pseudomonas lipase was significantly retarded. The distributed PLLA micro spheres were enlarged and amorphous. The thermal behavior of the blend by microwave heating revealed that PCL and PLLA underwent a melting process, which induced the variations of the PCL phase and PLLA spheres. The weight loss caused by degradation of the PCL/PLLA blend obtained by conventional methods (B50c) is greater than that of the blend obtained by microwave methods (B50m), which reflects the change in morphology from a loose PCL network (B50c) to a dense PCL plank (B50m).     

Electrospun fiber mats of poly(3‐hydroxybutyrate), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), and their blends

Electrospinning of poly(3‐hydroxybutyrate) (PHB), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and their blends was first carried out in chloroform at 50 °C on a stationary collector. The average diameter of the as‐spun fiber from PHB and PHBV solutions decreased with increasing collection distance and increased with increasing solution concentration and applied electrical potential. In all of the spinning conditions investigated, the average diameter of the as‐spun pure fibers ranged between 1.6 and 8.8 μm. Electrospinning of PHB, PHBV, and their blends was carried out further at a fixed solution concentration of 14% w/v on a homemade rotating cylindrical collector. Well‐aligned, cross‐sectionally round fibers without beads were obtained. The average diameter of the as‐spun pure and blend fibers ranged between 2.3 and 4.0 μm. The as‐spun fiber mats appeared to be more hydrophobic than the corresponding films and much improvement in the tensile strength and the elongation at break was observed for the blend fiber mats over those of the pure fiber ones. Lastly, indirect cytotoxicity evaluation of the as‐spun pure and blend fiber mats with mouse fibroblasts (L929) indicated that these mats posed no threat to the cells. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2923–2933, 2006     

Modification of hydrophilic poly(vinyl alcohol) film via blending with hydrophobic poly(butyl acrylate-co-methyl methacrylate)

A series of poly(vinyl alcohol)/poly(butyl acrylate-co-methyl methacrylate) [PVA/P(BA-co-MMA)] blend films with different P(BA-co-MMA) content were prepared by the solution casting method. Surface morphologies of the PVA/P(BA-co-MMA) blend films were studied by scanning electron microscopy and atomic force microscopy. Thermal, mechanical, and chemical properties of PVA/P(BA-co-MMA) blend films were investigated by differential scanning calorimeter, thermogravimetric analysis, tensile tests, and surface contact angle tests. It was revealed that the introduction of P(BA-co-MMA) could affect the properties of the PVA films. The results also showed that, when P(BA-co-MMA) mole content is 3 %, the tensile strength and the surface contact angle of the polymer blend film are 20.4 MPa and 43.5°, respectively, suggesting that the polymer blend film holds both a better mechanical property and a better chemical property.     

Biodegradability of poly(3-hydroxybutyrate) film grafted with vinyl acetate: Effect of grafting and saponification

Radiation-induced graft polymerization of vinyl acetate (VAc) onto poly(3-hydroxybutyrate) (PHB) film was carried out. At a degree of grafting higher than 5%, the grafted films (PHB-g-VAc) completely lost the enzymatic degradability that is characteristic of PHB due to the grafted VAc covering the surface of the PHB film. However, the biodegradability of the PHB-g-VAc films was recovered when the films were saponified in alkali solution under optimum conditions. Graft chains of the PHB-g-VAc film reacted selectively to become biodegradable polyvinyl alcohol (PVA). The biodegradability of the saponified PHB-g-VAc film increased rapidly with time.     

New chitin-based polymer hybrids, 1. Miscibility of poly(vinyl alcohol) with chitin derivatives

As a new class of biopolymer-based hybrid materials, the present paper describes the binary blends of a modified chitin and poly(vinyl alcohol) (PVA) which are miscible in the whole range of compositions. The blend films were prepared by the solvent cast method from a homogeneous aqueous solution of PVA and a chitin derivative having poly(2-methyl-2-oxazoline) side chains. Miscibility between PVA and poly(2-methyl-2-oxazoline) homopolymer was also revealed. Differential scanning calorimetry and FT-IR analyses were used to investigate the blends.     

Novel biodegradable poly(butylene succinate)/poly(ethylene oxide) blend film with compositional and spherulite‐size gradients

Biodegradable poly(butylene succinate) (PBS)/poly(ethylene oxide) (PEO) polymer blend film with compositional gradient in the film thickness direction was prepared using a method of interdiffusion across the interface between the PBS and PEO layers at a temperature above the melting points of both the component polymers. The miscibility between PBS and PEO was confirmed by observation of the glass transition temperature by differential scanning calorimetry. The compositional gradient structure of PBS/PEO was characterized by microscopic mapping measurement of Fourier transform infrared spectra and dynamic mechanical thermal analysis. Furthermore, a new method for confirming the crystalline/crystalline compositional gradient structure through observing the crystallization behavior by POM (polarized optical microscopy) was put forward. A continuous gradient of the spherulite size along the film thickness direction was succeessfully generated in the PBS/PEO blend film. The compositional gradient blend was found to have significantly improved physical properties that cannot be realized for pure PBS, pure PEO, and even their homogeneous miscible blend system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 368–377, 2005     

Effect of poly(vinyl alcohol) fine particles as a novel biodegradable nucleating agent on the crystallization of poly(3‐hydroxybutyrate)

The effect of poly(vinyl alcohol)(PVA) fine particles as the nucleating agent on the crystallization behavior of bacterial poly(3‐hydroxybutyrate)(PHB) was studied using differential scanning calorimetry measurements and polarized light microscope observation. The results were compared with the effect of PVA conventionally blended with PHB. The PVA fine particles were found to be able to greatly enhance the crystallization of PHB, while the conventionally blended PVA extremely retarded the crystallization of PHB. The nucleating effect of PVA fine particles is almost comparable to that of the talc powder. Considering the biodegradability and biocompatibility of PVA, the usage of PVA particle as a nucleating agent provides marked benefits over the currently employed nonbiodegradable nucleating agents, such as talc and boron nitride. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44:1813–1820, 2006     

Polyaniline/poly(vinyl alcohol) (PAN/PVA) composite films: the synergy of film structural stiffening, redox amplification, and mobile species compositional dynamics

In this work, we report an unexpected but significant improvement of the redox behavior of conducting polyaniline (PAN) films by trapping intrinsically nonconducting poly(vinyl alcohol) (PVA) in the matrix of the polymer acting as stiffening and/or cross-linking agents. Film structural stiffening of PAN/PVA inclusion was studied in relation to film compositional dynamics. PAN and PAN/PVA composite films were potentiodynamically deposited using high-frequency electrochemical quartz crystal microbalance under electrochemical potentiodynamic control. From the simultaneously obtained measurements of nanogravimetric and cyclic voltammetric data, it has been found that the presence of PVA in the deposition solution increased the rate of PAN film growth as a function of PVA concentration. Characterization of the resultant composite films in monomer-free acidic electrolyte solutions showed significantly enhanced redox behavior of PAN/PVA composite films (with different PVA contents) compared to pure PAN by a factor of ～2–4. For the study of structure–composition relationships of composite polymer films, fluxes of instantaneous mobile species dynamics (ion/solvent) as a function of film redox conversion and potential cycling were correlated with film structural stiffening and the observed unusual redox enhancement of PAN/PVA composite films. Using various experimental timescales, we were able to resolve bound (associated with ion transfer) and free solvent compositional dynamics (associated with thermodynamic activity balance).     

Miscibility and thermal stability of poly(vinyl alcohol)/chitosan mixtures

The miscibility and the thermal behaviour of chitosan acetate (ChA) with poly(vinyl alcohol) (PVA) have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Chitosan is blended with poly(vinyl alcohol) in acetic acid solution and this solution is cast to prepare the blend film. From thermal curves the thermal transitions: T_g, T_m and characteristic temperatures of decomposition: T_di, T_max have been determined and compared. The influence of the degree of PVA hydrolysis on the thermal properties of blend systems has been discussed.Based upon the observation on the DSC analysis, the melting point of PVA is decreased when the amount of ChA in the blend film is increased. Though some broadening of the transition curves could be noticed (DSC, TGA and DMA), the obtained results suggest that in the solid ChA/PVA blends the components are poorly miscible. Only PVA sample with relatively low DH = 88% and hence low degree of crystallinity shows partial miscibility with ChA of relatively low molecular weight.     

Properties stability and biodegradation behaviors of soy protein isolate/poly (vinyl alcohol) blend films

The objective of this work was to investigate the color, transparency, water sensitivity and mechanical properties stability in air under photo-oxidative degradation influencing consumer acceptance and biodegradation behaviors in soil of soy protein isolate (SPI)/poly (vinyl alcohol) (PVA) blend packaging films during 30 days. The results showed that PVA could dilute the yellow color and make the SPI-based films less darkness in application and the transparency of SPI/PVA films at various stages of degradation was improved. The addition of PVA decreased the ability of SPI protein molecules to absorb water and enhanced the mechanical properties of blend films comparing to pure SPI film in 30 days. Aerobic biodegradation of films in soil proved that the PVA compound interacting with protein imposed negative effects on biodegradation of blend films prolonging their decomposing time. The SPI/PVA blend films decomposed into small fragments of less complex molecules along with surface completely digested after 30 days.     

Structure and Mechanical Properties of Chitosan/Poly(Vinyl Alcohol) Blend Films

Summary: The origins of the thermal and mechanical properties of chitosan and poly(vinyl alcohol) (PVA) with inter- and intra-hydrogen bonds were investigated systematically by using X-ray, DSC, positron annihilation and viscoelastic measurements. Based on their individual properties, the characteristics of the blend films were estimated in relation to their morphology and mechanical properties as a function of chitosan content. The characteristics of the blend films were also analyzed in terms of the deviation from a simple additive rule of chitosan and PVA content. These results suggested that the miscibility of chitosan and PVA could be ensured by entanglement of the amorphous chain segments of chitosan and PVA. Further detailed analysis revealed that the chitosan content on the film surface is higher than that of the admixture content of chitosan after elongation, although the chitosan and PVA chains were crystallized independently. The elongation could be achieved for the blend films whose PVA content was higher than 50% and the drawn blend films were transparent. Thus, it may be expected that sufficiently entangled meshes formed between chitosan and PVA amorphous chains within the film, the PVA content being higher than 50%, were maintained under the elongation process.     

Rheo-optical FT-IR spectroscopy of poly(3-hydroxybutyrate)/poly(lactic acid) blend films

The orientation of poly(3-hydroxybutyrate) (PHB) and poly(lactic acid) (PLA) segments in PHB/PLA blend films cast from chloroform solutions with compositions PHB < PLA was studied during uniaxial elongation up to 250% strain at 50 °C by in-situ rheo-optical FT-IR spectroscopy. From the orientation functions of the ν(CO) bands of the blend components, it was derived that the PLA chains orient in the direction of elongation while the PHB chains orient perpendicular to the drawing direction. PHB homopolymer and PHB/PLA blend films with PHB > PLA compositions could only be oriented by cold drawing in ice water after quenching from the melt. The IR-dichroic effects of films drawn under these conditions indicate for both blend components a chain alignment parallel to the drawing direction.     

壳聚糖-聚羟基丁酸酯共混膜的制备与性质

以乙酸为共溶剂,制备了壳聚糖-聚羟基丁酸酯(CTS-PHB)共混膜,利用红外光谱(FT-IR)、广角X粉末衍射(WAXD)、扫描电镜(SEM)及差热分析(DTA)表征了共混膜的化学组成、晶形、形貌和热稳定性能。研究表明:CTS和PHB可在体积百分数为62.5%的乙酸溶液中共混,形成表面光滑、不透明的膜,干态共混膜具备一定的力学强度。各比例的CTS-PHB共混膜有相同的热分解温度,共混膜的形貌特征随两组分质量配比变化,其中mPHB/mCTS=1/1的共混膜显示出良好的有序结构。     

Effect of aging on fractional crystallization of poly(ethylene oxide) component in poly(ethylene oxide)/poly(3‐hydroxybutyrate) blends

The effect of aging on the fractional crystallization of the poly(ethylene oxide) (PEO) component in the PEO/poly(3‐hydroxybutyrate) (PHB) blend has been investigated. The partial miscibility of the PEO/PHB blends with high PEO molecular weight (M_v = 2.0 × 10⁵ g/mol) was confirmed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis. The fractional crystallization behavior of the PEO component in the PEO/PHB blends with low PEO content (not more than 30 wt% of PEO), before and after aging under vacuum at 25 °C for 6 months, were compared by DSC, fourier transform infrared microscopic spectroscopy, small angle X‐ray diffraction, and scanning electron microscopy. It was confirmed that nearly all the PEO components remain trapped within interlamellar regions of PHB for the PEO/PHB blends before aging. Under this condition, the crystallization of PEO is basically induced by much less active heterogeneities or homogeneous nucleation at high supercoolings. While, after the same PEO/PHB samples were stored at 25 °C in vacuum for 6 months, a part of the PEO component was expelled from the interlamellar region of PHB. Under this condition, the expelled PEO forms many separate domains with bigger size and crystallizes at low supercoolings by active heterogeneous nucleation, whereas the crystallization of PEO in the interlamellar region is still mainly induced by less active heterogeneities or homogeneous nucleation at extreme supercoolings. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2665–2676, 2005     

Spontaneous thinning/thickening deformation observed for plastic blend films and some factors affecting film deformation

The fully amorphous films of highly syndiotactic poly[(R,S)‐3‐hydroxybutyrate] (s‐PHB)/atactic poly(4‐vinylphenol) (PVPh) blends show reversible thinning/thickening phenomena at 37 °C in aqueous medium. On the other hand, isotactic poly[(R)‐3‐hydroxybutyrate] (i‐PHB)/PVPh blend film, in which i‐PHB blend component was partially crystalline, did not show any thinning/thickening phenomena under the same conditions. To elucidate the factors influencing these phenomena, the structure and molecular interaction in these blends were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry, and wide‐angle X‐ray diffraction. The FTIR spectra indicated that the ester carbonyl of PHB and the phenolic hydroxyl of PVPh formed hydrogen bonds in both the thinned and thickened s‐PHB/PVPh blend films. The blend composition, intermolecular hydrogen‐bonding interaction, crystallization behavior, miscibility, and the glass‐transition temperature of the blends affected the thinning/thickening phenomena. Some other polyesters such as poly(?‐caprolactone), poly (L‐lactic acid), atactic poly(D,L‐lactic acid), and poly(ethylene terephthalate) had no ability to exhibit thinning/thickening phenomena in water at 37 °C when they were blended with PVPh. This result implies that s‐PHB/PVPh is the rare example with the ability to show reversible thinning/thickening phenomena. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2736–2743, 2002     

Structure and compatibility of poly(vinyl alcohol)-silk fibroin (PVA/SA) blend films

The structure and compatibility of poly(vinyl alcohol)-silk fibroin (PVA/SF) blend films were analyzed by differential scanning calorimetry (DSC), thermomechanical (TMA) and thermogravimetric (TGA) analysis, x-ray diffractometry, and scanning (SEM) and transmission (TEM) electron microscopy. DSC curves of PVA/SF blend films showed a major endothermic peak at 220°C, along with a peak at 280°C. These endotherms were assigned to the thermal decomposition of the ordered PVA elements and to the thermal degradation of silk fibroin, respectively. The PVA/SF blends behaved in a manner intermediate to the pure components, as suggested by both contraction expansion and sample weight retention properties recorded by TMA and TGA measurements. The IR absorption spectra of the blends were identified as purely a composite of the absorption bands characteristic of both PVA and SF pure polymers. The X-ray diffraction patterns of PVA/SF blends showed overlapping spacing due to PVA and SF. A dispersed phase formed by spherical particles of 3–7 μm diameter was observed by SEM and TEM. All these findings suggest that PVA and SF are incompatible. © 1994 John Wiley & Sons, Inc.