Plasticized waxy maize starch: effect of polyols and relative humidity on material properties

The plasticizing effect of different polyols such as glycerol, xylitol, sorbitol, and maltitol on waxy maize starch was investigated. The concentration of plasticizer was fixed at 33 wt % (dry basis of starch). The structure and mechanical performance of resulting films conditioned at different relative humidity levels were studied in detail. The effect of the plasticizer on the glass-rubber transition temperature (T(g)) and crystallinity was characterized using differential scanning calorimetry. It was found that T(g) decreases with increasing moisture content and decreasing molecular weight of the plasticizer. The water resistance of starch increased steadily with the molecular weight of the plasticizer and was directly proportional to the ratio of the end to total hydroxyl groups. As the molecular weight of the plasticizer increased, the brittleness of the dry system increased. However, the use of high molecular plasticizer allowed good mechanical properties of the moist material to be obtained in terms of both stiffness and elongation at break.     

Flexible oxygen barrier films from spruce xylan

Arabinoglucuronoxylan was extracted from Norway spruce and films prepared by casting from aqueous solution. The sugar analysis and NMR confirmed that the spruce xylan was composed of arabinose, 4-O-methyl-glucuronic acid and xylose in a ratio of 1:2:11 respectively. Substitutions of 4-O-methyl-α-d-GlcpA at O₂ and of α-l-Araf at O₃ on the xylose backbone were found by NOE analysis. NOE cross-peaks indicated as well that there is at least one free xylose on the main chain present between two substitutions. Whether the distribution of side chains was random or in blocks was uncertain. The average molecular weight of the sample was determined by size exclusion chromatography to be 12,780 g/mol. Arabinoglucoronoxylan casting yielded transparent flexible films with an average stress at break of 55 MPa, strain at break of 2.7% and a Young's Modulus 2735 MPa. Wide-angle X-ray scattering analysis showed that the arabinoglucuronoxylan films were totally amorphous. Addition of sorbitol as plasticizer resulted in less strong but more flexible films (strain at break of 5%). Peaks of crystallinity could be seen in X-ray which corresponds to sorbitol crystallizing in distinct phases. The dynamic mechanical analysis showed that the arabinoglucuronoxylan film softened at a later relative humidity (80% RH) in comparison with plasticized films (60% RH). The films showed low oxygen permeability and thus have a potential application in food packaging.     

Preparation and study of novel biodegradable blends based on gelatinized starch and 1,4-trans-polyisoprene (gutta percha) for food packaging or biomedical applications

The gas and water vapour permeability coefficients of novel biodegradable films based on 1,4-trans-polyisoprene and gelatinized starch were determined. The glass transitions, indirectly determined from gas permeability measurements, were compared to those obtained from thermal measurements (differential thermal analysis and dynamic mechanical thermal analysis). Incorporation of a low plasticizer amount in the blend was attempted in order to improve the mechanical properties of the blends. Some initial biodegradability experiments showed that these novel blends are biodegradable. This is primarily due to the presence of starch.     

Development of Orodispersible Films Containing Benzydamine Hydrochloride Using a Modified Solvent Casting Method

The aim of this study was to develop benzydamine hydrochloride-loaded orodispersible films using the modification of a solvent casting method. An innovative approach was developed when the drying process of a small-scale production was used based on a heated inert base for casting the film. During this process, two types of film-forming maltodextrins for rapid drug delivery were used. They were plasticized with two different polyols (xylitol and sorbitol). Superdisintegrant Kollidon® CL-F was tested as an excipient that can induce faster disintegration of the prepared films. The influence of the formulation parameters (dextrose equivalent of film-forming maltodextrins, a type of plasticizer, and the presence of superdisintegrant) on the disintegration time, mechanical properties, and moisture content of films was statistically evaluated using a multivariate data analysis. Orodispersible films containing maltodextrin with lower dextrose equivalent value showed better mechanical properties (tensile strength ranged from 886.6?±?30.2 to 1484.2?±?226.9 N cm^?2), lower moisture content (0.5?±?0.0 to 1.2?±?0.2%), and shorter disintegration time (17.6?±?2.9 to 27.8?±?2.8 s). Films plasticized with xylitol showed shorter disintegration time (17.6?±?2.9 to 29.2?±?3.8 s) than films containing sorbitol (23.8?±?2.9 to 31.7?±?3.9 s). With the addition of superdisintegrant Kollidon® CL-F, a significant influence on disintegration time was not observed. The modified solvent casting method shows great promise in a small-scale laboratory production of orodispersible films, e.g., in a pharmacy lab.     

Nanocomposite films based on xylan-rich hemicelluloses and cellulose nanofibers with enhanced mechanical properties

Interest in xylan-rich hemicelluloses (XH) film is growing, and efforts have been made to prepare XH films with improved mechanical properties. This work described an effective approach to produce nanocomposite films with enhanced mechanical properties by incorporation of cellulose nanofibers (CNFs) into XH. Aqueous dispersions of XH (64-75 wt %), sorbitol (16-25 wt %), and CNF (0-20 wt %) were cast at a temperature of 23 °C and 50% relative humidity. The surface morphology of the films was revealed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermal properties and crystal structure of the films were evaluated by thermal analysis (TG) and X-ray diffraction (XRD). The surface of XH films with and without CNF was composed primarily of nanonodules, and CNFs were embedded in the XH matrix. Freeze-dried XH powder was amorphous, whereas the films with and without CNF showed a distinct peak at around 2θ = 18°, which suggested that XH molecules aggregated or reordered in the casting solution or during water evaporation. Furthermore, the nanocomposite films had improved thermal stability. XH film with 25 wt % plasticizer (sorbitol, based on dry XH weight) showed poor mechanical properties, whereas incorporation of CNF (5-20 wt %, based on the total dry mixture) into the film resulted in enhanced mechanical properties due to the high aspect ratio and mechanical strength of CNF and strong interactions between CNF and XH matrix. This effective method makes it possible to produce hemicellulose-based biomaterials of high quality.     

Extrusion of pectin/starch blends plasticized with glycerol

The microstructural and thermal dynamic mechanical properties of extruded pectin/starch/glycerol (PSG) edible and biodegradable films were measured by scanning electron microscopy (SEM) and thermal dynamic mechanical analysis (TDMA). SEM revealed that the temperature profile (TP) in the extruder and the amount of water present during extrusion could be used to control the degree to which the starch was gelatinized. TDMA revealed that moisture and TP during extrusion and by inference the amount of starch gelatinization had little effect on the mechanical properties of PSG films. Furthermore, TDMA revealed that PSG films underwent a glass transition commencing at about −50°C and two other thermal transitions above room temperature. Finally, it was concluded that the properties of extruded PSG films were comparable to those cast from solution.     

Biodegradable films of partly branched poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer: modulation of phase morphology, plasticization properties and thermal depolymerization

We report on the modulation of phase morphology, plasticization properties, and thermal stability of films of partly branched poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer (PLLA-co-PCL) with additions of low molecular weight compounds, namely, triethyl citrate ester, diethyl phthalate, diepoxy polyether (poly(propylene glycol) diglycidyl ether), and with epoxidized soybean oil (ESO). The PLLA-co-PCL/polyether films showed significant stability against thermal depolymerization, high film flexibility, and good plasticizing properties, probably due to cross-linking and chain branching formation between diepoxy groups with both the end carboxyl and hydroxyl groups of the PLLA copolymer (initially present or generated during the degradation process) to produce primary ester and ether bonds, respectively. Diethyl phthalate and triethyl citrate ester were found to be efficient plasticizers for PLLA copolymer in terms of glass transition and mechanical properties, but the more water-soluble plasticizer triethyl citrate induced a dramatic loss in the molecular weight of the copolymer. Although ESO cannot play the role of a plasticizer, it substantially stabilizes and retards thermal depolymerization of the PLLA copolymer matrix, possibly because of a reaction between epoxy groups with the end carboxyl and hydroxyl groups of the PLLA copolymer. The presence of ESO in PLLA-co-PCL/ESO/triethyl citrate blends enhanced the compatibility and miscibility of the plasticizer with the PLLA copolymer matrix, considerably improved the mechanical properties (elongation at break), and substantially stabilized the copolymer against thermal depolymerization. It seems likely that the epoxy groups interact not only with the end hydroxyl and carboxyl group of the copolymer but as well with the hydroxyl group of triethyl citrate plasticizer to produce a new ether bond (C-O-C) as the cross-linking unit. On the other hand, for PLLA-co-PCL/ESO/polyether blends, (80/10/10) epoxidized oil distorts the compactness of the blend by diminishing the proposed entanglements between carboxyl, hydroxyl, and diepoxy groups of polyether and reduces the high elongation properties otherwise observed in the PLLA-co-PCL/polyether films. The multicomponent approach toward modulating poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer films using epoxy compounds and plasticizers and the insight into the nature of various PLLA matrixes presented here offer advantages to a broad engineering of PLLA copolymer films having desirable physical properties and multiphase behavior for efficient uses in future technical applications.     

Effect of polysaccharide structure on mechanical and thermal properties of galactomannan-based films

Films were prepared from guar gum and locust bean gum galactomannans. In addition, enzymatic modification was applied to guar gum to obtain structurally different galactomannans. Cohesive and flexible films were formed from galactomannans plasticized with 20-60% (w/w of polymer) glycerol or sorbitol. Galactomannans with lower galactose content (locust bean gum, modified guar gum) produced films with higher elongation at break and tensile strength. The mechanical properties of films were improved statistically significantly by decreasing the degree of polymerization of guar gum with mannanase treatments (4 h) of 2 and 10 nkat/g, whereas 50 nkat/g produced films with low elongation at break and tensile strength. Galactomannans with approximately 6 galactose units per 10 mannose backbone units resulted in films with 2 peaks in loss modulus spectra, whereas films from galactomannans with approximately 2 galactose groups per 10 mannose units behaved as a single phase in dynamic mechanical analysis.     

Effect of water content on the structural reorganization and elastic properties of biopolymer films: a comparative study

In this work, the effect of water uptake on the structural reorganization and elastic properties of three types of biopolymer films was studied. The water-biopolymer interaction for hydroxypropyl cellulose (HPC), gelatin, and cassava starch films prepared from aqueous solutions was studied and compared using Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction, dynamic vapor sorption (DVS), and dynamic mechanical thermal analysis with humidity generator and controller (DMTA) techniques. The FTIR spectral variations due to the water sorption were generalized into two-dimensional (2D) correlation graphs for each biopolymer, and the effect of water on the molecular conformation was compared. The water sorption isotherms were fitted with Guggenheim-Anderson-De Boer (GAB) and D'Arcy and Watt models. The water content in the mono- and multilayers predicted by both models for each biopolymer was discussed and compared. The correlation of the fitted data obtained from the sorption isotherms to the DMTA data allowed us to conclude that the elastic properties of the HPC films depended on the total water content in contrast to the elastic properties of the gelatin and cassava starch films, which decrease only with the appearance of multilayer water.     

Extrusion of pectin and glycerol with various combinations of orange albedo and starch

Microstructural and mechanical properties of extruded pectin and glycerol films with various combinations of orange albedo and starch were determined by universal mechanical testing (UMT), dynamic mechanical analysis (DMA), optical microscopy (OM) and scanning electron microscopy (SEM). A glass transition and a second order transition attributed to the onset of translational motion of the pectin molecules was observed in all films. Observation by OM suggested that extrusion in the presence of dilute HCl was more effective in disintegrating albedo than either water or dilute citric acid. UMT, DMA and SEM analysis revealed that extruded pectin/albedo/starch/glycerol films provided better mechanical properties than pectin/albedo/glycerol films and were comparable in mechanical properties to extruded pectin/starch/glycerol films.     

Stabilization of hot-melt extrusion formulations containing solid solutions using polymer blends

This study was aimed at enhancing the physical stability of the drug clotrimazole (CT) and the polymer contained within hot-melt extrusion (HME) films using polymer blends of hydroxypropyl cellulose (HPC) and poly(ethylene oxide) (PEO). The HME films were investigated for solid-state characteristics, moisture sorption, bioadhesivity, mechanical properties, glass transition temperature, release characteristics, and physical and chemical stability of the drug and the polymer within the HME films. The solid-state characterization of the drug and the polymer was performed using differential scanning calorimetry, x-ray diffractometry, and dynamic mechanical analysis. A texture analyzer was used to study the bioadhesive and mechanical properties of the HME films. The physical and chemical stability of the films, stored at 25°C/60% relative humidity or in a desiccator, was studied for up to 12 months. CT was found to be in solid solution within all of the formulations extruded. The physical stability of the drug and PEO in the HME films increased with increasing HPC concentration, but the bioadhesivity and flexibility of the PEO films decreased with increasing HPC concentration. Films containing HPC: PEO∶CT in the ratio of 55∶35∶10 demonstrated optimum physical-mechanical, bioadhesive, and release properties. In conclusion, polymer blends of HPC and PEO were used successfully to tailor the drug release, mechanical and bio-adhesive properties, and stability of the HME films. Published: June 29, 2007     

Solid-state and mechanical properties of aqueous chitosan-amylose starch films plasticized with polyols

The film-forming ability of chitosan and binary mixtures of chitosan and native amylose corn starch (Hylon VII) was evaluated with free films prepared by a casting/solvent evaporation method. Unplasticized and plasticized free chitosan films in aqueous acetic acid and respective films containing a mixture of chitosan and native amylose starch in acetic acid were prepared. Glycerol, sorbitol, and i-erythritol were used as plasticizers. Solid-state and mechanical properties of the films were studied by powder x-ray diffractometry (XPRD), differential scanning calorimetry (DSC), and a materials testing machine. The films composed of a mixture of chitosan and native amylose starch in acetic acid were clear and colorless. A plasticizer concentration of 20% wt/wt (of the polymer weight) ws sufficient to obtain flexible films with all samples tested. X-ray diffraction patterns and DSC thermograms indicated an amorphous state of the films independent of the type of plasticizer used. In conclusion, incorporation of native amylose com starch into chitosan films improves the consistency and the mechanical properties of the films.     

Structure–properties relationship in cross-linked high amylose starch cast films

Cross-linked high amylose starch cast films were prepared to study the effect of cross-linking degree on various properties in normal environmental conditions. Mechanical tensile properties (Young's modulus, elongation at break, tensile strength), water vapour transmission rate (WVTR) and oxygen permeability coefficients of cast films were determined as a function of cross-linking degree and percentage of free humidity. Cross-linking degree and degree of crystallinity are closely related and seem to have non-negligible opposite effect on the properties of interest. By using increased amounts of cross-linking agents, the effect of cross-linking degree tends to reduce the degree of crystallinity modulating thus mechanical properties, water vapour permeability and oxygen permeability coefficients. Yield strength, tensile strength at break, WVTR versus cross-linking degree showed a non-monotonous behaviour. Maximal values for these properties were reached for moderate cross-linking degree. Optimal crystalline/amorphous ratio in the films may induce interactions and balanced effects, which would be responsible for the non-linear behaviour of some of the investigated properties. By cross-linking with epichlorohydrin in the range 1–10 g crosslinker/100 g polymer, the mechanical properties of films are still related to water content and water vapour permeability remains high compared to some synthetic polymeric materials.     

Gliadins polymerized with cysteine: effects on the physical and water barrier properties of derived films

To study the effects of disulfide bonds on certain functional properties of films made from the wheat gluten proteins gliadin and glutenin, cysteine was used to promote the formation of interchain disulfide bridges between gliadins in 70% ethanolic solution. Disulfide-mediated polymerization of gliadins was confirmed by means of SDS-PAGE analysis. After chemical treatment of gliadins, films were solution cast and the effects of both glycerol (used as a plasticizer) and relative humidity were studied on water vapor permeability, moisture sorption isotherms at 23 degrees C, and the optical properties of the films. The results were compared with those obtained from analogous films made from untreated glutenin macromolecules. Cysteine-mediated polymerization of gliadins improved the water vapor resistance of films achieving values close to those obtained for glutenin films. Development of intra- and interchain disulfide bonds did not change the moisture sorption capacity of the films but transparency was slightly diminished.     

Effect of transglutaminase treatment on the properties of cast films of soy protein isolates

The objective of this work was to investigate the effect of microbial transglutaminase (MTGase) treatment on the properties and microstructures of soy protein isolate (SPI) films cast with 0.6 plasticizer per SPI (gg(-1)) of glycerol, sorbitol and 1:1 mixture of glycerol and sorbitol, respectively. Tensile strength (TS), elongation at break (EB), water vapor transmission rate (WVTR) or water vapor permeability (WVP), moisture content (MC), total soluble matter (TSM), lipid barrier property and surface hydrophobicity of control and MTGase-treated films were evaluated after conditioning film specimens at 25 degrees C and 50% relative humidity (RH) for 48 h. The treatment by 4 units per SPI (Ug(-1)) of MTGase increased the TS and surface hydrophobicity by 10-20% and 17-56%, respectively, and simultaneously significantly (P< or =0.05) decreased the E, MC and transparency. The WVTR or TSM of SPI films seemed to be not significantly affected by enzymatic treatment (P>0.05). The MTGase treatment also slowed down the moisture loss rate of film-forming solutions with various plasticizers during the drying process, which was consistent with the increase of surface hydrophobicity of SPI films. Microstructural analyses indicated that the MTGase-treated films of SPI had a rougher surface and more homogeneous or compact cross-section compared to the controls. These results suggested that the MTGase treatment of film-forming solutions of SPI prior to casting could greatly modify the properties and microstructures of SPI films.     

Cassava bagasse cellulose nanofibrils reinforced thermoplastic cassava starch

Cellulose cassava bagasse nanofibrils (CBN) were directly extracted from a by-product of the cassava starch (CS) industry, viz. the cassava bagasse (CB). The morphological structure of the ensuing nanoparticles was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), presence of other components such as sugars by high performance liquid chromatography (HPLC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) experiments. The resulting nanofibrils display a relatively low crystallinity and were found to be around 2–11 nm thick and 360–1700 nm long. These nanofibrils were used as reinforcing nanoparticles in a thermoplastic cassava starch matrix plasticized using either glycerol or a mixture of glycerol/sorbitol (1:1) as plasticizer. Nanocomposite films were prepared by a melting process. The reinforcing effect of the filler evaluated by dynamical mechanical tests (DMA) and tensile tests was found to depend on the nature of the plasticizer employed. Thus, for the glycerol-plasticized matrix-based composites, it was limited especially due to additional plasticization by sugars originating from starch hydrolysis during the acid extraction. This effect was evidenced by the reduction of glass vitreous temperature of starch after the incorporation of nanofibrils in TPSG and by the increase of elongation at break in tensile test. On the other hand, for glycerol/sorbitol plasticized nanocomposites the transcrystallization of amylopectin in nanofibrils surface hindered good performances of CBN as reinforcing agent for thermoplastic cassava starch. The incorporation of cassava bagasse cellulose nanofibrils in the thermoplastic starch matrices has resulted in a decrease of its hydrophilic character especially for glycerol plasticized sample.     

Fabrication and Characterization of Native and Oxidized Potato Starch Biodegradable Films

The need to replace conventional polymers due to environmental pollution caused by them has led to increased production of biodegradable polymers such as starch. Thus, the application possibilities of starch have increased. In this study, we produced and characterized biodegradable films derived from native and oxidized potato starch. The film-forming solution was prepared with different concentrations of extracted starch (native or oxidized) and a plasticizer (glycerol or sorbitol). Then, the mechanical, barrier, morphological, and structural properties of the films were characterized. The moisture content of the films varied from 15.35?±?1.31 to 21.78?±?0.49%. The elastic modulus of the films ranged from 219?±?14.97 to 2299?±?62.91 MPa. The film of oxidized starch plasticized with sorbitol in the lowest content was the most resistant and flexible; moreover, this film also presented lower water vapor permeability and low solubility in water. Fourier-transform infrared spectroscopic analysis of the biodegradable films indicated the presence of same functional groups as those of starch with bands in the same regions. The film thickness was lower for the films plasticized with glycerol whereas the color variation (Δ?) was lower for the ones plasticized with sorbitol. In case of both plasticizers, the increase in their content decreased the Δ? value. All the biodegradable films presented stability against water absorption owing to their low solubility in water. Morphological evaluation revealed the presence of partially gelatinized starch granules in the films. The roughness parameter (Rq) of the films varied from 3.39 to 10.9 nm, indicating that their surfaces are smooth. X-ray diffraction studies showed a B-type pattern for the starches, which is representative of tubers. Further, the films present higher relative crystallinity (RC) compared to the starches. The biodegradable starch films are uniform, transparent and with low solubility in water. The oxidation of starch and use of sorbitol as a plasticizer resulted in improved properties of the starch films, which is suitable for application.     

Effect of solvent-dependent viscoelastic properties of chitosan membranes on the permeation of 2-phenylethanol

The viscoelastic behaviour of chitosan was followed by dynamic mechanical analysis (DMA) while the sample was immersed in gradient compositions of water/ethanol mixtures. The swelling equilibrium of chitosan membranes, both crosslinked with genipin or not, increased linearly with the water content. Increasing the water content, it was simultaneously observed a peak in the loss factor (around 25 vol.%) and a reduction of the storage modulus, which was attributed to the α-relaxation of chitosan. This was the first time that the glass transition dynamics in a polymer was monitored in immersion conditions where the composition of the plasticizer in the bath is changed in a controlled way. The water content at which tan δ presented a maximum increased with both increasing frequency and increasing crosslinking density. The permeability decreased steadily with the ethanol content, reaching very low values around the glass transition. Therefore we hypothesize that conformational mobility of the polymeric chains may play an important role in the diffusion properties of molecules trough polymeric matrices.     

Preparation and characteristics of oxidized potato starch films

Starch films were developed from oxidized potato starch (OPS) with glycerol as a plasticizer at different contents. The OPS films were transparent and flexible. The mechanical properties of these films were measured, and the results indicated that the film with 19.4% glycerol exhibited the desirable mechanical properties. X-ray diffraction study showed that the increase of glycerol content led to a decrease in the crystallinity for OPS films, and storage conditions such as storage time, storage temperature and relative humidity also had certain effects on the retrogradation of starch owing to re-crystallization. Anti-leakage, anti-crosslinking, and stability in acid or alkali solutions of the OPS films were also studied, and the results indicated that the OPS films had excellent anti-leakage ability for vegetable oil, good anti-crosslinking ability in saturated formaldehyde vapor, and good stability in acid aqueous medium, but poor stability in alkali aqueous medium.     

Properties of biodegradable citric acid-modified granular starch/thermoplastic pea starch composites

Pea starch-based composites reinforced with citric acid-modified pea starch (CAPS) and citric acid-modified rice starch (CARS), respectively, were prepared by screw extrusion. The effects of granular CAPS and CARS on the morphology, thermal stability, dynamic mechanical thermal analysis, the relationship between the mechanical properties and water content, as well as the water vapor permeability of the composite films were investigated. Scanning electron microscope and X-ray diffraction reveal that the reinforcing agents, the granules of CAPS and CARS, are not disrupted in the thermoplastic process, while the pea starch in the matrix is turned into a continuous TPS phase. Granular CAPS and CARS can improve the storage modulus, the glass transition temperature, the tensile strength and the water vapor barrier, but decrease thermal stability. CARS/TPS composites exhibit a better storage modulus, tensile strength, elongation at break and water vapor barrier than CAPS/TPS composites because of the smaller size of the CARS granules.