Surface esterification of corn starch films: Reaction with dodecenyl succinic anhydride

Surface of corn starch films was modified through esterification using dodecenyl succinic anhydride (DDSA) as reactant. The effects of reaction temperature and time, concentration of alkaline aqueous solution for activating starch, concentration of ethanol diluted DDSA, and time of alkaline aqueous solution treatment on the physical properties related to material’s hydrophilic nature, such as moisture absorption and surface water contact angle, were investigated. It was found that the surface esterification modification significantly reduced the moisture sensitivity and surface hydrophilic character of starch film. Due to the hydroxyl groups in the film surface layer were reacted with DDSA, the equilibrium moisture content of the starch film under 95% RH declined 22% and the surface water contact angle increased up to 82% after surface esterification modification.     

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).     

Influence of photocrosslinking on the retrogradation of wheat starch based films

The ageing of wheat starch based materials was followed as a function of time for different systems suitably hydrated to be in the rubbery state. In particular, one aspect of retrogradation, that is to say the development of crystallinity is analysed in order to study the influence of a specific crosslinking treatment of starch films made by UV irradiation (photocrosslinking). Mechanical and thermal properties showed that an important limitation on this particular ageing occurs after photocrosslinking at room temperature. A process of accelerated ageing, monitored by modulated DSC, was also performed at 60 °C in order to increase retrogradation kinetics. The results showed a recrystallisation decrease and it appeared that the presence of the plasticiser enhances retrogradation. For a plasticised sample (17% glycerol), a decrease of 30% of the melting enthalpy was observed compared to 91% for an unplasticised one. A modification in the nature of the melting peaks, as recorded by modulated DSC, allowed us to propose a model for amylopectin retrogradation after crosslinking.     

Hybrid complexes of photosynthetic reaction centers and quantum dots in various matrices: resistance to UV irradiation and heating

The effects of ultraviolet (UV) irradiation (up to 0.6 J/cm²) and heating (65 °C, 20 min) on the absorption spectra and electron transfer in dehydrated film samples of photosynthetic reaction centers (RCs) from purple bacterium Rhodobacter (Rb.) sphaeroides, as well as in hybrid structures consisting of RCs and quantum dots (QDs), have been studied. The samples were placed in organic matrices containing the stabilizers of protein structure—polyvinyl alcohol (PVA) and trehalose. UV irradiation led to partially irreversible oxidation of some RCs, as well as to transformation of some fraction of the bacteriochlorophyll (BChl) molecules into bacteriopheophytin (BPheo) molecules. In addition, UV irradiation causes degradation of some BChl molecules that is accompanied by formation of 3-acetyl-chlorophyll a molecules. Finally, UV irradiation destroys the RCs carotenoid molecules. The incorporation of RCs into organic matrices reduced pheophytinization. Trehalose was especially efficient in reducing the damage to the carotenoid and BChl molecules caused by UV irradiation. Hybrid films containing RC?+?QD were more stable to pheophytinization upon UV irradiation. However, the presence of QDs in films did not affect the processes of carotenoid destruction. The efficiency of the electronic excitation energy transfer from QD to P865 also did not change under UV irradiation. Heating led to dramatic destruction of the RCs structure and bacteriochlorins acquired the properties of unbound molecules. Trehalose provided strong protection against destruction of the RCs and hybrid (RC?+?QD) complexes.

     

Studies of chitosan: II. Preparation and characterization of chitosan/poly(vinyl alcohol)/gelatin ternary blend films

Chitosan/poly(vinyl alcohol)/gelatin (CS/PVA/GA) ternary blend films were prepared by solution blending method in this study. The thermal properties of the CS/PVA/GA ternary blend films were examined by differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The melting point of the CS/PVA/GA ternary blend film was increased when the amount of GA in the blend film was increased based upon the DSC thermal analysis. Results of X-ray diffraction (XRD) analyses indicated that the intensity of diffraction peak at 19 degrees of PVA became lower and broader with increasing the amount of GA in the CS/PVA/GA ternary blend film. Although CS, PVA, and GA are hydrophilic biodegradable polymers, the results of water contact angle measurements are still as high as 83 degrees, 68 degrees, and 66 degrees, respectively. A minimum water contact angle (56 degrees) was observed when the ternary blend film contains 50 wt.% GA (i.e. GA5). This behavior is primarily due to the reorientation of polar functional groups toward to the top surface of CS/PVA/GA ternary blend films.     

Mechanical properties of chitosan/bamboo charcoal composite films made with normal and surface oxidized charcoal

Chitosan/bamboo charcoal composite films were prepared by blending chitosan with either virgin bamboo charcoal or bamboo charcoal modified by nitric acid oxidation to provide more hydrophilic regions on the bamboo charcoal surface. Investigation of the physical properties of these composite films revealed that the tensile strength and Young’s modulus of the chitosan films were enhanced in a dose-dependent manner by the inclusion of modified bamboo charcoal at up to 1% (w/w), whilst the elongation at break was increased by inclusion of modified bamboo charcoal at up to 0.5% (w/w). In contrast, chitosan composites with virgin bamboo charcoal at up to 0.5% or 1.0% (w/w) showed no enhancement of the tensile strength or Young’s modulus, respectively, and both parameters were reduced with higher levels of virgin bamboo charcoal. Oil, and especially water, absorption of the composite films displayed a marked and dose-dependent increase compared to those of the pure chitosan film.     

Photoimmobilization of organophosphorus hydrolase within a PEG-based hydrogel.

Organophosphorous hydrolase (OPH) was physically and covalently immobilized within photosensitive polyethylene glycol (PEG)-based hydrogels. The hydroxyl ends of branched polyethylene glycol (b-PEG, four arms, MW = 20,000) were modified with cinnamylidene acetate groups to give water-soluble, photosensitive PEG macromers (b-PEG-CA). The b-PEG-CA macromers underwent photocrosslinking reaction and formed gels upon UV irradiation (>300 nm) in the presence of erythrosin B. Native OPH was pegylated with cinnamylidene-terminated PEG chains (MW = 3400) to be covalently linked with the b-PEG-CA macromers during photogelation. The effect of pegylation on the stability of the enzyme was determined. Furthermore, the effect of enzyme concentration, wavelength of irradiation, and photosensitizer on the stability of the entrapped enzyme was also investigated. The pegylated OPH was more stable than the native enzyme, and the OPH-containing gels exhibited superior stability than the soluble enzyme preparations.     

Physical, chemical and mechanical properties of pehuen cellulosic husk and its pehuen-starch based composites

Pehuen cellulosic husk was characterized and employed as reinforcement for composite materials. In this research, thermoplastic pehuen starch (TPS) and TPS/poly(lactic acid) (PLA)/polyvinyl alcohol (PVA) composites, reinforced with 5 and 10% of pehuen husk, were prepared by melt-blending. Comparative samples of pehuen TPS and TPS/PLA/PVA blend were also studied. Physical, thermal, structural and mechanical properties of composites were evaluated. Pehuen husk mainly consists of cellulose (50wt%), hemicellulose (30wt%) and lignin (14wt%). In respect to lipids, this husk has only a 0.6wt%. Its surface is smooth and damage-free and it is decomposed above 325°C. The incorporation of pehuen husk improved considerably the thermal stability and mechanical properties of the studied composites, mainly in TPS composites. Their thermal stability enhances since biofiber hinders the "out-diffusion" of volatile molecules from the polymer matrix, while mechanical properties could raise due to the natural affinity between husk and starch in the pehuen seed.     

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%.     

Development of films based on blends of Amaranthus cruentus flour and poly(vinyl alcohol)

The aim of this work was to develop biodegradable films based on blends of Amaranthus cruentus flour and poly(vinyl alcohol). Five different PVA types were tested. Blends with higher hydrolysis (HD) degree PVA were more resistant, showing greater tensile strength (TS) and puncture force (PF). However, the films with PVA with lower HD showed more flexibility, greater elongation at break (ELO) and greater puncture deformation (PD), with the exception of PVA 325. The latter was chosen due to it superior mechanical performance (TS = 10.2 MPa, ELO = 89.8%, PF = 9.4 N and PD = 16.3%). When films based on blends of amaranth flour and PVA 325 (10–50%) were evaluated, all mechanical properties were enhanced with increase in PVA 325 content. The solubility in water of the films made with PVA and amaranth flour decreased with increasing PVA content, reaching 44% of soluble matter for the 50% PVA film. The formation of hydrogen bonds between the blend components was confirmed by the FTIR spectra analysis.     

Rectified photocurrent of molecular photodiode consisting of cytochrome c/GFP hetero thin films

Photoinduced electron transfer in the molecular electronic device consisting of protein-adsorbed hetero Langmuir–Blodgett (LB) film was investigated. Three kinds of functional molecules, cytochrome c, viologen, and green fluorescent protein (GFP) were used as an electron acceptor, a mediator, and a sensitizer, respectively. The hetero-LB film was fabricated by subsequently depositing cytochrome c and viologen onto the pretreated ITO or quartz glass. GFP adsorbed hetero-LB films were prepared by soaking the hetero-LB films into the buffer solution containing GFP. The MIM (metal/insulator/metal) structured molecular device was constructed by depositing aluminum onto the surface of the GFP-adsorbed hetero LB films. Due to the excitation by irradiation with a 460 nm monochromic light source, the photoinduced unidirectional flow of electrons in the MIM device could be achieved and was detected as photocurrents. The photoswitching function was achieved and the rectifying characteristic was observed in the molecular device. Based on the measurement of transient photocurrent of molecular device, the unidirectional flow of electrons was verified.     

Palladium adsorbing properties of UV-curable chitosan derivatives and surface analysis of chitosan-containing paint

The results of X-ray photoelectron spectroscopy (XPS) analyses indicated that palladium chloride was adsorbed on a plastic surface coated with a chitosan-containing paint (C-Paint), and was completely reduced to Pd(0) after reduction with dimethylamine-borane. To improve the stability and hardening properties of C-Paint, UV-curable chitosan derivatives, such as N-[3-methoxy-4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]methylated chitosan and N-(3-methoxy-4-methacryloyloxyphenyl)methylated chitosan, were synthesized. The derivatives showed better affinity for organic solvents. After UV irradiation for 20s, an acidic solution of these derivatives was transformed to a gel, and the dried films exhibited good palladium(II) adsorption at pH 1.1.     

Enzymatic grafting of hexyloxyphenol onto chitosan to alter surface and rheological properties

An enzymatic method to graft hexyloxyphenol onto the biopolymer chitosan was studied. The method employs tyrosinase to convert the phenol into a reactive o-quinone, which undergoes subsequent nonenzymatic reaction with chitosan. Reactions were conducted under heterogeneous conditions using chitosan films and also under homogeneous conditions using aqueous methanolic mixtures capable of dissolving both hexyloxyphenol and chitosan. Tyrosinase was shown to catalyze the oxidation of hexyloxyphenol in such aqueous methanolic solutions. Chemical evidence for covalent grafting onto chitosan was provided by three independent spectroscopic approaches. Specifically, enzymatic modification resulted in (1) the appearance of broad absorbance in the 350-nm region of the UV/vis spectra for chitosan films; (2) changes in the NH bending and stretching regions of chitosan's IR spectra; and (3) a base-soluble material with (1)H-NMR signals characteristic of both chitosan and the alkyl groups of hexyloxyphenol. Hexyloxyphenol modification resulted in dramatic changes in chitosan's functional properties. On the basis of contact angle measurements, heterogeneous modification of a chitosan film yielded a hydrophobic surface. Homogeneously modified chitosan offered rheological properties characteristic of associating water-soluble polymers.     

Photodynamic inactivation of Candida albicans using bridged polysilsesquioxane films doped with porphyrin

Novel photoactive bridged polysilsesquioxane films were prepared by doped with a porphyrin derivative. The films were formed by acid-catalyzed polycondensation reaction of a precursor of a bridged silsesquioxane, based on the reaction product of (glycidoxypropyl)trimethoxysilane with n-dodecylamine in the presence of 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin, followed by solvent evaporation. This procedure allowed obtaining flexible thin films. Absorption and fluorescence spectroscopic analysis showed the characteristic bands of the porphyrin in the visible region indicating that the photosensitizer is mainly embedded as monomer in the films. Photodynamic properties of the polymeric films were studied in solution containing photooxidizable substrates. Singlet molecular oxygen, O(2)((1)Δ(g)), production was observed by the reaction with 9,10-dimethylanthracene and 9,10-anthracenediyl-bis(methylene)dimalonic acid in different media. Also, these films photosensitized the decomposition of l-tryptophan. In vitro investigations showed that these films produce photodynamic inactivation of Candida albicans cells in aqueous suspensions and on their surfaces. These films exhibit a photosensitizing activity causing a ～2.5 log (99.7%) decrease of cellular survival after 60 min of irradiation with visible light. Also, the photocytotoxicity of the surfaces was tested under condition of microbial growth. Yeast cells exposed to the film and illuminated showed growth delay compared with controls. Studies of photodynamic action mechanism showed that the photoinactivation increased in D(2)O, while cells were protected in the presence of azide ion. In contrast, the addition of mannitol produced a negligible effect on the cellular phototoxicity. These results provide evidence that O(2)((1)Δ(g)) produced by the polymeric film doped with porphyrin can successfully inactivate C. albicans in cell suspensions and deposited on the film surface.     

Biocomposites of cellulose reinforced starch: improvement of properties by photo-induced crosslinking

In the present study, the composite films have been prepared from the aqueous dispersions of starch with microcrystalline cellulose using glycerol as plasticizer and irradiated under ultraviolet (UV) light using sodium benzoate as photo-sensitizer. Photo-crosslinking was characterized by measuring the water absorption under 100% relative humidity, swelling degree and gel fraction in dimethylsulphoxide (DMSO), upon irradiation time. Both, the incorporation of cellulose and photo-irradiation were found to decrease the water absorption, swelling in DMSO and increase the gel fraction. Thermal transitions indicated the anti-plasticization of amylopectin chains at the fiber/matrix interface. With increasing content of cellulose and photo-irradiation time, the tensile modulus and strength were found to improve. It is summarized that the combination of cellulose reinforcement and photo-crosslinking of matrix has improved the physical and mechanical properties.     

Effect of water on the surface molecular mobility of poly(lactide) thin films: an atomic force microscopy study

Physical properties associated with molecular mobility on the surface of thin films with 300 nm thickness for poly(lactide)s (PLAs) were studied under vacuum conditions as well as under aqueous conditions by using friction force mode atomic force microscopy (AFM). Two types of PLAs were applied for the experimental samples as uncrystallizable PLA (uc-PLA) and crystallizable PLA (c-PLA). The friction force on the surface of thin films was measured as a function of temperature to assess the surface molecular mobility both under vacuum and under aqueous conditions. A lower glass-transition temperature of the uc-PLA surface in water was detected than that under vacuum conditions. In the case of the c-PLA thin film, change in friction force was detected at a lower temperature under aqueous conditions than in vacuo. A morphological change was observed in the c-PLA thin film during heating process from room temperature to 100 degrees C by temperature-controlled AFM. The surface of the c-PLA thin film became rough due to the cold crystallization, and the crystallization of c-PLA molecules in water took place at a lower temperature than in vacuo. These friction force measurements and AFM observations suggest that molecular motion on the surface of the both uc- and c-PLA thin films is enhanced in the presence of water molecules. In addition, in situ AFM observation of the enzymatic degradation process for the c-PLA thin film crystallized at 160 degrees C was carried out in buffer solution containing proteinase K at room temperature. The amorphous region around the hexagonal crystal was eroded within 15 min. It has been suggested that the adsorption of water molecules on the PLA film surface enhances the surface molecular mobility of the glassy amorphous region of PLA and induces the enzymatic hydrolysis by proteinase K.     

Effect of axially coordinated pi-acid ligands on photovoltaic properties of Zn-tetraphenylporphyrin

Following our earlier observations that the well known doping effect of oxygen and water on electrical properties of porphyrin and phthalocyanine films may be attributed to a pi-acid axial interaction throughout the film in the case of PdTPP, we have compared Zn-TPP films supported on transparent n-doped SnO₂ electrodes which had been treated with several pi-acids in contact with an electrolyte to give photoelectrochemical cells. Photovoltages obtained in contact with a series of solution couples were used to obtain approximate photo flat band potentials. The doped films were examined by magnetic circular dichroism (MCD) spectroscopy so that the electronic effect of the dopant could be diagnosed. It was found that pi-acid dopants cause shifts to low energy in the band which indicates “hole stabilization” in the order pyridine < CO < triphenylarsine. The potentials of zero photopotential ‘E_FB’, correlate approximately with spectral shifts. It is concluded that manipulation of axial ligand dopants is a promising method for design of metal porphyrin and perhaps phthalocyanine films with desired photovoltaic properties.     

Thermal helix-coil transition in UV irradiated collagen from rat tail tendon

The thermal helix-coil transition in UV irradiated collagen solution, collagen film and pieces of rat tail tendon (RTT) were compared. Their thermal stability’s were determined by differential scanning calorimeter (DSC) and by viscometric measurements. The denaturation temperatures of collagen solution, film and pieces of RTT were different. The helix-coil transition occur near 40°C in collagen solution, near 112°C in collagen film, and near 101°C in pieces of RTT. After UV irradiation the thermal helix-coil transition of collagen samples were changed. These changes depend on the degree of hydratation.     

Biocomposites of thermoplastic starch with surfactant

Thermoplastic starch films were prepared by a casting technique. Microfibrillated fibers from husks of corncobs were added as reinforcing agents and glyceryl monostearate (GMS) as surfactant. The films were characterized using X-ray diffraction studies, thermal and mechanical analysis and water uptake experiments. Differential scanning calorimetry (DSC) and X-ray diffraction showed the formation of amylose–GMS complexes. Compared to films without GMS the films with GMS showed significant reductions in water uptake and an increase in tensile strength. Important differences in the DSC measurements in the 160–200 °C range of films with and without GMS were also exhibited. These effects can be related to the reinforcement of the polymer matrix by the web-like network of the microfibrillated fibers, the formation of amylose–GMS complexes and the interactions of the polar groups of the GMS with the hydroxyl groups of the cellulose. Retrogradation tendencies of the TPS films were also changed by these phenomena.     

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.