Preparation and characterization of ultra violet (UV) radiation cured bio-degradable films of sago starch/PVA blend

Polymer films of sago starch/polyvinyl alcohol (PVA) were prepared by casting and cured under ultra violet (UV) radiation. Different blends were made varying the concentration of sago starch and PVA. Tensile strength (TS) and elongation at break (Eb) of the prepared films were studied. Films made up of sago starch and PVA with a ratio of 1:2 showed the highest TS and Eb. The physico-mechanical properties of prepared films were improved by grafting with acrylic monomers with the aid of UV radiation. A series of formulations was prepared with two monomers 2-ethyl 2-hydroxymethyl 1,3 methacrylate (EHMPTMA) and 2-ethylhexylacrylate (EHA) and a photoinitiator. Monomer concentration, soaking time and radiation dose were optimized in terms of grafting and mechanical properties. The highest TS was at 50% EHMPTMA and 48% EHA and 2% photo initiator at 5 min soaking time and recorded value was 6.58 MPa. The prepared films were further characterized with NMR spectroscopy and scanning electron microscope (SEM).     

Effect of gelatinization and additives on morphology and thermal behavior of corn starch/PVA blend films

The blend films of ungelatinized and gelatinized starch/polyvinyl alcohol (PVA) were prepared with a solution casting method by the introduction of additives (glycerol/urea) or not. The phase morphologies and thermal behaviors of the blends were carefully analyzed. A droplet phase was observed in the blends containing ungelatinized starch and a laminated phase was observed in the blends containing gelatinized starch. For both ungelatinized and gelatinized starch/PVA blends, the melting temperature (T(m)) (210-230°C) of PVA was detected, and the T(m) of gelatinized starch/PVA blends was higher than that of the ungelatinized starch/PVA blends. Blend films containing 16.8wt% of glycerol or urea exhibited a decreased T(m). The introduction of additives (glycerol or urea) reduced the decomposition onset temperature of the blend films. These various morphologies and thermal behaviors could be attributed to the different hydrogen bonding interaction characteristics between starch and polyvinyl alcohol at different conditions.     

A combination of gamma irradiation and CaCl2 immersion for a pectin-based biodegradable film

Using citrus pectin a biodegradable film was prepared by a combination treatment of gamma irradiation (0, 10, 20, and 30 kGy) and CaCl₂ immersion (0, 5, and 10%) cross-linking. The tensile strength of the pectin-based film was the highest in the 5% CaCl₂ treatment at 20 kGy of an irradiation dose. The tensile strength of the film with CaCl₂ was generally higher than that of the non-CaCl₂ treatment. The elongation at break and water vapor permeability were the lowest at a CaCl₂ of 5% among the irradiated treatments. The total organic carbon content produced from the Paenibacillus polymyxa and Pseudomonas aeruginosa showed that the film of the 20 kGy-irradiated film was lower than those of the 0, 10, and 30 kGy-irradiated films. In conclusion, irradiation of the film casting solution at 20 kGy combined with a 5% CaCl₂ immersion resulted in film with improved mechanical properties and biodegradability.     

Nanofibers from blends of polyvinyl alcohol and polyhydroxy butyrate as potential scaffold material for tissue engineering of skin

Nanofibers were prepared by electrospinning from pure polyvinyl alcohol (PVA), polyhydroxybutyrate (PHB), and their blends. Miscibility and morphology of both polymers in the nanofiber blends were studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC), revealing that PVA and PHB were miscible with good compatibility. DSC also revealed suppression of crystallinity of PHB in the blend nanofibers with increasing proportion of PVA. The hydrolytic degradation of PHB was accelerated with increasing PVA fraction. Cell culture experiments with a human keratinocyte cell line (HaCaT) and dermal fibroblast on the electrospun PHB and PVA/PHB blend nanofibers showed maximum adhesion and proliferation on pure PHB. However, the addition of 5 wt % PVA to PHB inhibited growth of HaCaT cells but not of fibroblasts. On the contrary, adhesion and proliferation of HaCaT cells were promoted on PVA/PHB (50/50) fibers, which inhibited growth of fibroblasts.     

Synthesis of antibacterial PVA/CM-chitosan blend hydrogels with electron beam irradiation

A series of excellent hydrogels were prepared from poly(vinyl alcohol) (PVA) and carboxymethylated chitosan (CM-chitosan) with electron beam irradiation (EB) at room temperature. Electron spectroscopy analysis of the blend hydrogels revealed that good miscibility was sustained between CM-chitosan and PVA. The properties of the prepared hydrogels, such as the mechanical properties, gel fraction and swelling behavior were investigated. The mechanical properties and equilibrium degree of swelling improved obviously after adding CM-chitosan into PVA hydrogels. The gel fraction determined gravimetrically showed that a part of CM-chitosan was immobilized onto PVA hydrogel. The further analyses of FTIR and DSC spectra of the prepared gels after extracting sol manifested that there was a grafting interaction between PVA and CM-chitosan molecules under irradiation. The antibacterial activity of the hydrogels against Escherichia coli was also measured via optical density method. The blend hydrogels exhibited satisfying antibacterial activity against E. coli, even when the CM-chitosan concentration was only 3 wt%.     

Imaging and thermal studies of wheat gluten/poly(vinyl alcohol) and wheat gluten/thiolated poly(vinyl alcohol) blends

The morphology of wheat protein (WG) blends with polyvinyl alcohol (PVA) and respectively with thiolated polyvinyl alcohol (TPVA) was investigated by atomic force (AFM) and transmission electron microscopy (TEM) as well as by modulated dynamic scanning calorimetry (MDSC). Thiolated additives based on PVA and other substrates were previously presented as effective means of improving the strength and toughness of compression molded native WG bars via disulfide-sulfhydryl exchange reactions. Consistent with our earlier results, AFM and TEM imaging clearly indicate that the addition of just a few mole percent of thiol to PVA was sufficient to dramatically change its compatibility with wheat protein. Thus, TPVA is much more compatible with WG and phase separates into much smaller domains than in the case of PVA, although there are still two phases in the blend: one WG-rich phase and another TPVA-rich phase. The WG/TPVA blend has phase domains ranging in size from 0.01 to 0.1 microm, which are roughly 10 times smaller than those of the WG/PVA blend. MDSC further illustrates the compatibilization of the protein with TPVA via the dependence of the transition temperatures on composition.     

Synthesis and evaluation of physicochemical properties of cross-linked sago starch

Highly substituted sago starch phosphate was synthesized using POCl₃ as cross-linking reagent. Titrimetric and Fourier transform infra red (FT-IR) spectral analysis were used to characterize the substitution. Studying the different factors affecting the reaction parameters showed that the optimal conditions for starch phosphorylation were: 4 h reaction time and reagent concentration 1.5% (w/w). The physicochemical properties of cross-linked sago starch (CLSS) were done using Scanning electron micrograph (SEM), X-ray powder diffractometer (XRD and Thermogravimetric analysis (TGA). The results revealed that crystalline nature of native sago starch was transformed after cross-linking. TGA report exhibited higher thermal stability, which makes it suitable for various industrial applications. Swelling behavior showed high swelling at low temperature (30 and 60 °C) as compared to high temperature (90 °C).     

Effects of glyoxal cross-linking on baked starch foam

Starch trays and plates were prepared from native corn starch and corn starch cross-linked with glyoxal at different concentrations (0.126, 0.269, 0.271, 0.468 g/kg) using a foam baking process. The effect of cross-linking on baking parameters, including density, colour, water absorption, and tensile and flexural properties, was determined. Also, the morphologies of the trays were examined using a scanning electron microscope. Cross-linking considerably reduced the baking time, density and water absorption of the trays. Trays made from starch cross-linked with 0.126 and 0.269 g/kg glyoxal presented the best properties, with a homogenous microstructure and smooth surface quality. These trays had the lowest density (0.27 g/cm³) and had approximately 53% reduction in water absorption. Moreover, both the tensile and flexural strain of these foams was significantly higher than other foams.     

Miscibility studies of HPMC/PVA blends in water by viscosity, density, refractive index and ultrasonic velocity method

Hydroxy propyl methyl cellulose (HPMC)/polyvinyl alcohol (PVA) blends are edible polymer films used for food packing and directly in foodstuffs. However they are water-soluble in ordinary temperature and have good mechanical properties. The miscibility of HPMC/PVA blend in water was studied by viscosity, ultrasonic velocity, density and refractive index techniques at 30 and 50 °C. Using viscosity data, the interaction parameters μ and α were calculated. These values revealed that HPMC/PVA blend is miscible when the HPMC content is more than 60% in the blend at 30 and 50 °C. And also the result revealed that the change in temperature has no significant effect on the miscibility of HPMC/PVA polymer blend.     

Interfacial properties of cell culture media with cell-protecting additives

In an effort to identify key rheological properties that contribute to cell protection against shear damage, we have measured surface shear and dilatationai viscosities, dynamic surface tension, foaminess, and foam stability for media containing cell-protecting additives. In a companion article,(18) we found that cell-to-bubble attachment was decreased in media containing Methocel, Pluronic F68, or polyvinyl alcohol (PVA). In medium containing polyethylene glycol (PEG) or potyvinyl-pyrrolidone (PVP), attachment was increased. PEG, PVP, serum (FBS), and serum albumin (BSA) increased the surface viscosity of the air/medium surface (thus, producing a more rigid interface), whereas F68 and PVA lowered it greatly. Foaming experiments showed that Methocel, PEG, PVA, and F68 decreased the foam half-life while FBS, BSA, and PVP were foam stabilizers. Interestingly, the foam stability of CHO cell suspensions decreased significantly for cell concentrations higher than ca. 2 x 10(6) cells/mL. Nonviable CHO cells reduced foam stability further. Dynamic surface tension values of the media tested were found significantly differentfrom their static surface tension values. The interfacial properties measured and the results presented in the companion study suggest that the additives that lower dynamic surface tension the most (Methocel, F68, and PVA) correlate well with reduced cell-to-bubble attachment, and thus, cell protection. Reduced dynamic surface tension with these additives implies faster surfactant adsorption, mobile interfaces, lower surface viscosity, and foam destabilization. Because PEG and PVP resulted in increased cell-to-bubble attachment and had different interfacial properties, a different mechanism (compared with Methocel, PVP, and F68) is apparently responsible for their protective effect. Finally, cell protection offered by FBS and BSA is attributed to the foam stabilization properties provided by these additives. (c) 1995 John Wiley & Sons Inc.     

The radiation crosslinked films based on PLLA/PDLA stereocomplex after TAIC absorption in supercritical carbon dioxide

The absorption of triallyl isocyanurate (TAIC) to equimolar stereo blends of PLLA and PDLA (sb-PLA samples) with crosslinker (TAIC) was controlled by supercritical carbon dioxide (sc-CO₂) treatment. The well-mixed sb-PLA/TAIC (sc-PLA) samples containing certain ratios of TAIC were obtained after vacuum evaporation. The sc-PLA samples were become much softer by sc-CO₂ treatment. The crosslinked sc-PLA materials with different crosslinking density were prepared by irradiation treatment at different radiation doses. Gel fraction, thermal properties and mechanical properties of crosslinked samples were investigated with different sc-PLA samples irradiated at the same radiation dose of 30 kGy and sc-PLA3 irradiated at different radiation doses. The crosslinking network inhibited crystallization, and enhanced the rigidity as well as lowered brittleness of irradiated samples. Although tensile strength and Young’s modulus of sc-PLA are reduced by sc-CO₂ treatment, they are much improved by radiation crosslinking at a suitable dose and the crosslinked samples become harder and tougher. The typical crosslinked obtained from sc-PLA3 irradiated at 30 kGy reveals the best thermal stability with the improved mechanical properties.     

Analysis of cell-to-bubble attachment in sparged bioreactors in the presence of cell-protecting additives

To investigate the mechanisms of cell protection provided by medium additives against animal cell injury in sparged bioreactors, we have analyzed the effect of various additives on the cell-to-bubble attachment process using CHO cells in suspension. Cell-to-bubble attachment was examined using three experimental techniques: (1) cell-bubble induction time analysis (cell-to-bubble attachment times); (2) forming thin liquid films and observing the movement and location of cells in the thin films; and (3) foam flotation experiments. The induction times we measured for the various additives are as follows: no additive (50 to 500 ms), polyvinyl pyrrolidone (PVP: 20 to 500 ms), polyethylene glycol (PEG: 200 to 1000 ms), 3% serum (500 to 1000 ms), polyvinyl alcohol (PVA: 2 to 10 s), Pluronic F68 (5 to 20 s), and Methocel (20 to 60 s). In the thin film formation experiments, cells in medium with either F68, PVA, or Methocel quickly flowed out of draining thin liquid films and entered the plateau border. When using media with no additive or with serum, the flow of cells out of the thin liquid film and film drainage were slower than for media containing Pluronic F68. PVA, or Methocel. With PVP and PEG, the thin film drainage was much slower and cells remained trapped in the film. For the foam flotation experiments, a separation factor (ratio of cell concentration in the foam catch to that in the bubble column) was determined for the various additives. In the order of increasing separation factors (i.e., increasing cell attachment to bubbles), the additives are as follows: Methocel, PVA, Pluronic F68, 3% serum, serum-free medium with no additives, PEG, and PVP. Based on the results of these three different cell-to-bubble attachment experiments, we have classified the cell-protecting additives into three groups: (1) Pluronic F68, PVA, and Methocel (reduced cell-to-bubble attachment); (2) PEG and PVP (high or increased cell-to-bubble attachment); and (3) FBS (reduced cell attachment butslower drainage films compared with F68, PVA, and Methocel with some cell entrapment in those films). These phenomena are discussed in relation to the interfacial properties of the media reported in a companion Study (this issue). (c) 1995 John Wiley & Sons Inc.     

Extruding foams from corn starch acetate and native corn starch

Because of the hydrophilic characteristics of native starch foams and the cost of modifying starch, the uses of starch and modified starch foams are hindered. To decrease hydrophilicity and cost of starch foams, native corn starch was blended with starch acetate and extruded. A twin-screw mixing extruder was used to produce the foams. Native starch content, screw speed, and barrel temperature had significant effects on molecular degradation of starches during extrusion. The melting temperature of extruded starch acetate/native starch foam was higher (216 degrees C) than that for starch acetate (193.4 degrees C). Strong peaks in the X-ray diffractograms of extruded starch acetate/native starch foam suggested new crystalline regions were formed. Optimum conditions for high radial expansion ratio, high compressibility, low specific mechanical energy requirement, and low water absorption index were 46.0% native starch content, 163 rpm screw speed, and 148 degrees C barrel temperature.     

Effect of γ-irradiation on some physiochemical properties of konjac glucomannan

Konjac glucomannan (KGM) was irradiated at 5, 20, 50 and 100 kGy and the effects of γ-irradiation on some physiochemical properties of KGM were studied by using viscosimeter, colorimeter, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet (UV) spectroscopy, thermal gravimetric (TG) analysis and scanning electron microscopy (SEM). γ-irradiation led to significant degradation of KGM according to the significant reduction of the weight-average molecular weight (M_w). The apparent viscosity of KGM decreased with increasing dose, while the viscosity stability was improved after irradiation. The colour of KGM became more intense brown with increasing dose up to 20 kGy. FT-IR spectra indicated that γ-irradiation introduced no significant changes into the structure but UV spectra showed a distinct absorption peak at about 265 nm, increasing with irradiation dose, which was attributed to the formation of carbonyl groups or double bond. High irradiation dose (100 kGy) caused a small decrease of thermal stability but presented no visible fissures or splitting of KGM granules according to the TG analysis and SEM microphotographs.     

The enzymatic hydrolysis of starch-based PVOH and polyol plasticised blends

Thermoplastic starch (TPS) materials present several advantages to the plastic industry and when blended with other materials they can exhibit improved mechanical and moisture sensitivity properties compared to pure TPS materials. However, the biodegradability of these blends, through such processes as enzymatic degradation, needs to be characterised to ensure the beneficial properties of TPS are not compromised. The aims of the study were to investigate the effect of varying polyvinyl alcohol (PVOH) content and polyol type within the TPS blends on the rate and extent of starch enzymatic hydrolysis using enzymes α-amylase and amyloglucosidase. The results of this study have revealed that TPS:PVOH blends with a PVOH content at 50 wt% exhibited a significantly reduced rate and extent of starch hydrolysis. The results suggest that this may have been attributed to interactions between starch and PVOH that further prevented enzymatic attack on the remaining starch phases within the blend. The extent of starch hydrolysis was not significantly affected by polyol type, however, the rate of starch hydrolysis from the maltitol blend was significantly reduced compared to sorbitol and glycerol substrates.     

Compatible ternary blends of chitosan/poly(vinyl alcohol)/poly(lactic acid) produced by oil-in-water emulsion processing

Ternary compatible blends of chitosan, poly(vinyl alcohol), and poly(lactic acid) were prepared by an oil-in-water (O/W) emulsion process. Solutions of chitosan in aqueous acetic acid, poly(vinyl alcohol) (PVA) in water, and poly(lactic acid) (PLA) in chloroform were blended with a high-shear mixer. PVA was used as an emulsifier to stabilize the emulsion and to reduce the interfacial tension between the solid polymers in the blends produced. It proved to work very well because the emulsions were stable for periods of days or weeks and compatible blends were obtained when PVA was added. This effect was attributed to a synergistic effect of PVA and chitosan because the binary blends PVA/PLA and chitosan/PLA were completely incompatible. The blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), stress-strain tests, and Fourier transform infrared spectroscopy (FTIR). The results indicated that despite the fact that the system contained distinct phases some degree of molecular miscibility occurred when the three components were present in the blend.     

The anaerobic degradability of thermoplastic starch: polyvinyl alcohol blends: potential biodegradable food packaging materials

A systematic study on the anaerobic degradability of a series of starch:polyvinyl alcohol (TPS:PVOH) blends was performed to determine their fate upon disposal in either anaerobic digesters or bioreactor landfills. The aims of the study were to measure the rate and extent of solubilisation of the plastics. The extent of substrate solubilisation on a COD basis reached 60% for a 90:10 (w/w) blend of TPS:PVOH, 40% for 75:25, 30% for 50:50 and 15% for PVOH only. The rate of substrate solubilisation was most rapid for the 90:10 blend (0.041 h(-1)) and decreased with the amount of starch in the blend in the following order 0.034 h(-1)(75:25); 0.023 h(-1)(50:50). The total solids that remained after 900 h were 10 wt.% (90:10); 23 wt.% (75:25); 55 wt.% (50:50); 90 wt.% (0:100). Starch containing substrates produced a higher concentration of volatile fatty acids (VFAs) and biogas, compared to the 0:100 substrate. The major outcome was that PVOH inhibited the degradation of the starch from the blend.     

Preparation and properties of biodegradable foams from starch acetate and poly(tetramethylene adipate-co-terephthalate)

Biodegradable composite foams were prepared by extruding starch acetate, with degree of substitution (DS) 1.78, with poly(tetramethylene adipate-co-terephthalate) (EBC). The foams' chemical structures, thermal behaviors, and microstructures were investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). By measuring these properties, it was found that low EBC contents in the blends favored the miscibility of the two polymers, as characterized by (1) disappearance of EBC carbonyl peak and appearance of hydrogen-bonded EBC carbonyl groups in FTIR spectra; (2) an increase in T_g of starch acetate and the decreases in T_m values of starch acetate and EBC in DSC thermograms; and (3) formation of a homogeneous morphology in SEM. However, large amounts of EBC decreased the miscibility of these two polymers, as reflected by the foams' physical and mechanical properties. With a small amount of EBC, the foams had high radial expansion ratios (RER) and spring indices (SI) and low unit densities and compressibilities. Biodegradation rates of the composite foams decreased with the addition of EBC to starch acetate.     

Structural and mechanical properties of UV-photo-cross-linked poly(N-vinyl-2-pyrrolidone) hydrogels

Biocompatible poly( N-vinyl-2-pyrrolidone) (PVP) hydrogels have been produced by UV irradiation of aqueous polymer mixtures, using a high-pressure mercury lamp. The resulting materials have been characterized by a combination of experimental techniques, including rheology, small-angle neutron scattering (SANS), electron paramagnetic resonance (EPR), and pulsed gradient spin-echo nuclear magnetic resonance (PGSE-NMR), to put in evidence the relationship between the microstructural properties and the macrofunctional behavior of the gels. Viscoelastic measurements showed that UV photo-cross-linked PVP hydrogels present a strong gel mechanical behavior and viscoelastic moduli values similar to those of biological gels. The average distance between the cross-linking points of the polymer network was estimated from the hydrogels elastic modulus. However, SANS measurements showed that the network microstructure is highly inhomogeneous, presenting polymer-rich regions more densely cross-linked, surrounded by a water-rich environment. EPR and PGSE-NMR data further support the existence of these water-rich domains. Inclusion of a third component, such as glycerol, in the PVP aqueous mixture to be irradiated has been also investigated. A small amount of glycerol (<3% w/w) can be added keeping satisfactory properties of the hydrogel, while higher amounts significantly affect the cross-linking process.     

The effect of citric acid on the structural properties and cytotoxicity of the polyvinyl alcohol/starch films when molding at high temperature

A series of starch/polyvinyl alcohol (PVA) films, denoted SP films, with varying concentrations (5–30 wt%) of citric acid (CA) were solvent cast at 140 °C. The effects of CA on the chemical structure, thermal properties, swelling degree, mechanical properties, crystallinity, and cytotoxicity were investigated. Fourier-transform infrared (FT-IR) spectroscopy showed that an esterification took place between CA and starch (or PVA) during molding at 140 °C. This esterification and the multi-carboxyl structure of CA resulted in a chemical cross-linking of the blended system. Furthermore, the esterification occurred more easily between starch and CA as opposed to between the PVA and CA. The residual-free CA acted as a plasticizer for the starch and PVA. As compared to the hydroxyl groups on glycerol, the carboxyl groups on CA were capable of forming stronger hydrogen bonds between CA and other components, and this cross-linking and strong hydrogen bonding enhanced the thermal stability of the SP films. Consequently, the water absorbance decreased from 33% to 20% as the CA percentage increased from 5 to 30 wt%. When 5 wt% CA was added, the tensile strength of the sample increased from 39 to 48 MPa, but when even more CA was added (from 5 to 30 wt%), the tensile strength decreased from 48 to 42 MPa and the elongation at break increased from 102% to 208%. This was caused by the plasticizing effect of the residual-free CA in the blend. The cell relative growth rates of samples with varying CA concentrations exceeded 80% after 7 days of incubation, and this demonstrated that there was no significant toxicity on the cells’ growth when the CA content was less than 20 wt%.