Edible films made from natural resources; microcrystalline cellulose (MCC), methylcellulose (MC) and corn starch and polyols-Part 2

Aqueous blends of microcrystalline cellulose (MCC) or methyl cellulose (MC) and corn starch with or without polyols were extruded, hot pressed and studied, after their conditioning at different relative humidities, in terms of their thermal, mechanical and water and gas permeability properties. An increase in water or polyol content showed a considerable increase in percentage elongation but also a decrease in the tensile strength of films. The presence of high cellulose contents increased the tensile strength and decreased the water vapour transmission of films. The development of crystallinity with time resulted in a decrease of both gas and water permeability. Several semiempirical models for calculation of gas permeability and tensile strength and tensile and flexural moduli were applied. The obtained values were compared to those experimentally determined and with the ones reported in the literature. On several occasions, quite significant discrepancies were found which were attributed to differences in molecular weight, percentage crystallinity and polymorphism.     

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.     

Microwave-assisted modification of starch for compatibilizing LLDPE/starch blends

Modification of activated cassava starch (S) was performed by using octenyl succinic anhydride (OSA) at different starch/OSA ratios under microwave radiation. FTIR and titration results indicated that, within a reaction time of 7 min, degrees of substitution (DS) of about 0.045 may be achieved with 20% OSA. Subsequently, linear low density polyethylene/starch (LLDPE/S) blends were prepared employing succinylated starches (S-g-OSA) as compatibilizers. The morphology and mechanical properties of LLDPE/S blends with and without compatibilizer were compared. It was observed that the addition of 10% of compatibilizer with respect to the dispersed phase content led to a reduction of the starch phase size and to an improvement of the blends mechanical properties.     

Nano clay reinforced PCL/starch blends obtained by high energy ball milling

Sodium montmorillonite was incorporated into a poly(ε-caprolactone)–starch blend by means of a ball mill. The structural organization and physical (mechanical, thermal and barrier) properties were analyzed and correlated with the milling conditions. Scanning electron microscopy and X-ray characterization show that the milling process can improve the compatibilization between the PCL and the starch phases, while promotes the dispersion of clay minerals at nanometric level. The milling time strongly influences the mechanical and barrier properties. In particular, the best results in terms of elastic modulus and permeability coefficient were achieved with a complete delamination of the pristine clay structure. In summary, the milling process not only has demonstrated to be a promising compatibilization method for immiscible PCL–starch blends, but it can be also used to improve the dispersion of nanoparticles into the polymer blends.     

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.     

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.     

Green composite films prepared from cellulose,starch and lignin in room-temperature ionic liquid

A series of novel biobased composite films derived from cellulose, starch and lignin were prepared from an ionic liquid (IL), 1-allyl-3-methylimidazolium chloride (AmimCl) by coagulating in a nonsolvent condition. The ionic liquid can be recycled with a high yield and purity after the green film was prepared. The uniform design method was applied to investigate mechanical properties of the biobased composite films. The effect of each component and their associated interactive effects were investigated. The experimental results showed that contents of cellulose, lignin and starch had a significant influence on the mechanical properties of composite films. The composite films showed relatively excellent mechanical properties in dry and wet states owing to the mutual property supplement of different components. The composite films were characterized via FT-IR, X-ray diffraction (XRD) and scanning electron microscope (SEM). Their thermal stability and gas permeability were also investigated, and the results showed that the composite films had good thermal stability and high gas barrier capacity and give a CO₂:O₂ permeability ratio close to 1.     

Amylose content and chemical modification effects on thermoplastic starch from maize – Processing and characterisation using conventional polymer equipment

A design of experiments was performed on extruded starch based materials studied in a recently published article [Chaudhary, A. L., Miler, M., Torley, P. J., Sopade, P. A., & Halley, P. J. (2008). Amylose content and chemical modification effects on the extrusion of thermoplastic starch from maize. Carbohydrate Polymers, 74(4), 907–913] highlighting the effects of amylose content, chemical modification and extrusion on a range of maize starches. An investigation into the effects of starch type (unmodified 0–80% amylose starch; hydroxypropylated 80% amylose starch), screw speed and ageing after moulding on final product properties such as mechanical properties (Young’s modulus, maximum stress and strain at break), moisture absorption, morphology and retrogradation are included. A full factorial design was used to study these starch type, processing and final product property relationships. Microscopy was used to observe any morphological difference between the various starch types in thermoplastic starch (TPS) blends and X-ray diffraction (XRD) was used to observe changes in crystallinity over time (retrogradation). The results show that 0% amylose (waxy maize) and hydroxypropylated 80% amylose thermoplastic starches have mechanical properties comparable to that of low density polyethylene (LDPE) and high density polyethylene (HDPE), therefore these materials have the potential to be an environmentally friendly alternative to current polymer resins.     

Chitosan and gelatin based edible films: state diagrams, mechanical and permeation properties

Films of chitosan and gelatin were prepared by casting their aqueous solutions (pH≈4.0) at 60°C and evaporating at 22 or 60°C (low- and high-temperature methods, respectively). The physical (thermal, mechanical and gas/water permeation) properties of these composite films, plasticized with water or polyols, were studied. An increase in the total plasticizer content resulted in a considerable decrease of elasticity modulus and tensile strength (up to 50% of the original values when 30% plasticizer was added), whereas the percentage elongation increased (up to 150% compared to the original values). The low-temperature preparation method led to the development of a higher percentage renaturation (crystallinity) of gelatin which resulted in a decrease, by one or two orders of magnitude, of CO₂ and O₂ permeability in the chitosan/gelatin blends. An increase in the total plasticizer content (water, polyols) of these blends was found to be proportional to an increase in their gas permeability.     

The plasticizing effect of alginate on the thermoplastic starch/glycerin blends

Corn starch and corn starch–alginate (5–15%) blends plasticized with 35% glycerin were prepared, water was intentionally excluded from the formulations. Torque rheometry measurements were carried out during the processing of the blends in a batch counterrotating twin screw mixer. A progressive decrease in the plasticization energy of the blends was observed as the alginate content was increased, with a 5-fold decrease for the blend with the higher alginate content (15%). The steady state torque of the plasticized melted blends also showed a decrease as alginate content was increased; with a drastic drop occurring for the formulation with higher alginate content. After mixing, test specimens for mechanical, thermal and microstructural testing were made by compression molding. A decrease in the elastic properties and an increase in elongation at break and impact resistance was observed when alginate content was increased in the blends. The transition of the materials towards a more viscous behavior, as alginate content was increased, was confirmed by differential scan calorimetric analysis. For the corn starch–alginate blends glass transitions were detected in the temperature range −60 to −90 °C. Scanning electron microscopy was used to examine the morphology of cryofractured surfaces of the molded test specimens. A reduction of the granular crystalline structures typical of corn starch was observed as alginate content was increased in the blends. The experimental evidence presented in this work indicates that, when water is excluded from thermoplastic corn starch preparation, alginate acts synergistically with glycerin increasing the degree and efficiency of the plasticization process.     

Effect of fiber treatments on tensile and thermal properties of starch/ethylene vinyl alcohol copolymers/coir biocomposites

Coir fibers received three treatments, namely washing with water, alkali treatment (mercerization) and bleaching. Treated fibers were incorporated in starch/ethylene vinyl alcohol copolymers (EVOH) blends. Mechanical and thermal properties of starch/EVOH/coir biocomposites were evaluated. Fiber morphology and the fiber/matrix interface were further characterized by scanning electron microscopy (SEM). All treatments produced surface modifications and improved the thermal stability of the fibers and consequently of the composites. The best results were obtained for mercerized fibers where the tensile strength was increased by about 53% as compared to the composites with untreated fibers, and about 33.3% as compared to the composites without fibers. The mercerization improved fiber–matrix adhesion, allowing an efficient stress transfer from the matrix to the fibers. The increased adhesion between fiber and matrix was also observed by SEM. Treatment with water also improved values of Young’s modulus which were increased by about 75% as compared to the blends without the fibers. Thus, starch/EVOH blends reinforced with the treated fibers exhibited superior properties than neat starch/EVOH.     

In vitro assessment of the enzymatic degradation of several starch based biomaterials

The susceptibility of starch-based biomaterials to enzymatic degradation by amylolytic enzymes (glucoamylase and alpha-amylase) was investigated by means of incubating the materials with a buffer solution, containing enzymes at different concentrations and combinations, at 37 degrees C for 6 weeks. Two polymeric blends of corn starch with poly(ethylene-vinyl alcohol) copolymer and poly(epsilon-caprolactone), designated by SEVA-C and SPCL, respectively, were studied. The material degradation was characterized by gravimetry measurements, tensile mechanical testing, scanning electron microscopy (SEM), and Fourrier transform infrared-attenuated total reflectance (FTIR-ATR). The degradation liquors were analyzed for determination of reducing sugars, as a result of enzyme activity, and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to identify the degradation products. All of the analysis performed showed that starch polymeric blends are susceptible to enzymatic degradation, as detected by increased weight loss and reducing sugars in solution. alpha-Amylase caused significant changes on the overall mechanical properties of the materials, with a decrease of about 65% and 58% being observed in the moduli for SEVA-C and SPCL, respectively, when compared with the control (samples incubated in buffer only). SEM analysis detected the presence of fractures and pores at the material's surface as a result of starch degradation by amylolytic enzymes. FTIR spectra confirmed a decrease on the band corresponding to glycosidic linkage (-C-O-C-) of starch after incubation of the materials with alpha-amylase. In contrast, the incubation of the polymers in buffer only, did not cause significant changes on the material's properties and morphology. Comparing the two materials, SEVA-C exhibited a higher degradability, which is related to the physicochemical structure of the materials and also to the fact that the starch concentration is higher in SEVA-C. The identification of the degradation products by HPAEC-PAD revealed that glucose was the major product of the enzymatic degradation of starch-based polymers. alpha-Amylase, as expected, is the key enzyme involved in the starch degradation, contributing to major changes on the physicochemical properties of the materials. Nevertheless, it was also found that starch-based polymers can also be degraded by other amylolytic enzymes but in a smaller extent.     

Developing hydroxypropyl methylcellulose/hydroxypropyl starch blends for use as capsule materials

Blends of hydroxypropyl methylcellulose (HPMC) with up to 70% hydroxypropyl starch (HPS) were developed for use as hard capsule materials. Polyethylene glycol (PEG) was used as both a plasticizer and a compatibilizer in the blends. In order to prepare hard capsules for pharmaceutical application using the well-established method of dipping stainless steel mold pins into solution then drying at certain temperature, equilibrated solutions with higher solids concentration (20%) were investigated and developed. The solutions, films and capsules of the different HPMC/HPS blends were characterized by viscosity, transparency, tensile testing, water contact angle, SEM, as well as FTIR. The results showed that the blend system is immiscible but compatible in certain degree, especially after adding PEG. The hydroxypropylene groups grafted onto both cellulose and starch improved the compatibility between the HPMC and the modified starch. The higher viscosity of starch at lower temperature improved the viscosity balance of the system, which enlarged the operation window for the dipping–drying technique. The PEG increased the transparency and toughness of the various blends. By optimizing temperature and incubation time to control viscosity, capsules of various blends were successfully developed.     

Physical blends of starch graft copolymers as matrices for colon targeting drug delivery systems

Colon targeting drug delivery systems have attracted many researchers due to the distinct advantages they present such as near neutral pH, longer transit time and reduced enzymatic activity. Moreover, in recent studies, colon specific drug delivery systems are gaining importance for use in the treatment of local pathologies of the colon and also for the systemic delivery of protein and peptide drugs.In previous works, our group has developed different types of hydrophilic matrices with grafted copolymers of starch and acrylic monomers with a wide range of physicochemical properties which have demonstrated their ability in controlled drug release. Since the cost of synthesizing a new polymeric substance and testing for its safety is enormous, polymer physical blends are frequently used as excipients in controlled drug delivery systems due to their versatility. So, the aim of this work is to combine two polymers which offer different properties such as permeability for water and drugs, pH sensitivity and biodegradability in order to further enhance the release performance of various drugs. It was observed that these physical blend matrices offer good controlled release of drugs, as well as of proteins and present suitable properties for use as hydrophilic matrices for colon-specific drug delivery.     

Structure-properties relationship in cross-linked high-amylose starch for use in controlled drug release

Cross-linked high-amylose starch (CLHAS), obtained by high-amylose starch cross-linking, was recently introduced as an excipient (Contramid) for monolithic dosage forms that are able to control drug release over 18-24 h. These control properties are related to tablet swelling and are strongly dependent on the degree of the cross-linking of CLHAS. The permeability of solutes through CLHAS hydrogels depends on the chemical structure of the polymer. The aim of this study was to obtain a better understanding of how modifications in CLHAS molecular structures at the level of long-range and short-range order during the cross-linking and processing conditions relate to the release properties of the CLHAS matrices. Structural parameters such as crystallinity contribute significantly to the physical and mechanical aspects of starch products. X-ray diffractometry, FTIR spectroscopy, dissolution tests in vitro, and mechanical hardness (of dry tablets) were found to be sensitive to the cross-linking degree (cld) variation. Best release properties and highest mechanical hardness were obtained from CLHAS matrices with low-to-moderate crystallinity, where the V- and the B-type structures coexist with amorphous regions. X-ray and FTIR profiles of dry CLHAS powders were found to be predictive for release properties of CLHAS tablets.     

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.     

Compression molding and tensile properties of thermoplastic potato starch materials

The mechanical and melt flow properties of two thermoplastic potato starch materials with different amylose contents were evaluated. The materials were prepared by mixing starch, glycerol, and water, mainly in the weight proportions of 10:3:4.5. Compression molding was used to produce sheets/films with a thickness in the range of 0.3-1 mm. After conditioning at 53% relative humidity (RH) and 23 C, the glycerol-plasticized sheets with a higher amylose content (HAP) were stronger and stiffer than the normal thermoplastic starch (NPS) with an amylose content typical for common potato starch. The tensile modulus at 53% RH was about 160 MPa for the high-amylose material and about 120 MPa for the plasticized NPS. The strain at break was about 50% for both materials. The stress at break was substantially higher for the HAP materials than for the NPS materials, 9.8 and 4.7 MPa, respectively. Capillary viscometry at 140 C showed that the high-amylose material had a higher melt viscosity and was more shear-thinning than the NPS. Dynamic mechanical measurements indicated a broad transition temperature range for both types of starch material. The main transition peaks for glycerol-plasticized starch were located at about room temperature with the transition for the HAP material being at a somewhat higher temperature than that of the NPS material with a lower amylose content. It was also noted that the processing conditions used during the compression molding markedly affected the mechanical properties of the starch material.     

Preparation and properties of starch acetate fibers for potential tissue engineering applications

This article reports the development of fibers from starch acetates that have mechanical properties and water stability better than most polysaccharide‐based biomaterials and protein fibers used in tissue engineering. In this research, starch acetates with three different degrees of substitution (DS) have been used to develop fibers for potential use as tissue engineering scaffolds. Varying the DS of starch acetate will provide fibers with different mechanical properties, hydrophilicity, and degradation behavior. Fibers made from DS 2.3 and 2.8 starch acetates have mechanical properties and water stability required for tissue engineering applications. The starch acetate fibers support the adhesion of fibroblasts demonstrating that the fibers would be suitable for tissue engineering and other medical applications. Biotechnol. Bioeng. 2009;103: 1016–1022. © 2009 Wiley Periodicals, Inc.     

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.     

Graft copolymers of starch and its application in textiles

The graft copolymerization of styrene (ST), methyl methacrylate (MMA)/butyl acrylate (BA) with starch was carried chemically using ferrous ion-peroxide redox system. The grafting was performed at 60 °C and the monomer ratios of ST/MMA and ST/BA was varied with their % composition as 80/20, 50/50 and 20/80 parts by weight. The effect of initiator concentration, starch concentration and the monomer ratio on the grafting efficiency was studied. The grafted starch granules (GSG) were further analyzed for their particle size, bulk density and by sizing on cotton yarn for its physico-mechanical properties such as tensile strength, elongation at break, etc. The rheological properties of the resulting granular product in water as well as the starch graft copolymer emulsion were studied.