Preparation of starch-based polyurethane films and their mechanical properties

In this study, polyurethane films were prepared using starch as the main polyol component, and the mechanical properties of these films were investigated. The starch content of the polyols was 30–50 wt%. To confirm the formation of a urethane linkage between the −OH of starch and −NCO of toluene 2,4-diisocyanate, Fourier transform infrared (FT-IR) spectroscopic analysis was performed. Differential scanning calorimetry (DSC) thermograms of the polyurethanes resulted in two endothermic peaks, which shifted to higher temperatures with increasing starch content and −NCO/−OH molar ratio. Due to the melting behavior of polyurethane, films could be prepared by hot pressing at an appropriate temperature. Polyurethane films were prepared with various polyol starch content and −NCO/−OH molar ratios. Tensile testing indicated that the breaking stress and elastic modulus increased significantly with starch content and −NCO/−OH molar ratio. In addition, bending tests indicated an increase in breaking stress and bending modulus with starch content and −NCO/−OH molar ratio and decreased breaking strain. The strain rate in both tensile and bending tests had a significant effect on the mechanical properties.     

Physical properties of zein films containing salicylic acid and acetyl salicylic acid

Zein films containing salicylic acid (SA) and acetyl salicylic acid (ASA) between 2 and 10% (initial zein weight basis) with or without glycerol were evaluated for structure, mechanical and dissolution properties. The random coils, α helices and β sheets mainly governed the secondary structure of zein, depending on glycerol and level of model molecules. Adding ASA resulted in an increase in α helices whereas β sheets increased at the expense of α helices when SA was used. Including SA or ASA decreased the tensile strength and the stiffness of films containing glycerol indicating the synergistic effect of SA and ASA. The strain at failure decreased with increasing content of SA but increased with increasing level of ASA. The dissolution properties were glycerol and drug dependent. ASA release in comparison to SA was quite low. The release was only observed above 10% ASA whereas it was detected in all films containing SA. The possible interactions between active components and proteins are discussed together with their implications on the physical properties of zein films.     

Improving the barrier and mechanical properties of corn starch-based edible films: Effect of citric acid and carboxymethyl cellulose

The films produced from pure starch are brittle and difficult to handle. Chemical modifications (e.g. cross-linking) and using a second biopolymer in the starch based composite have been studied as strategies to produce low water sensitive and relatively high strength starch based materials. A series of corn starch films with varying concentrations (0-20%, W/W) of citric acid (CA) and carboxymethyl cellulose (CMC) were produced by casting method. The effects of CA and CMC on the water vapor permeability (WVP), moisture absorption, solubility and tensile properties were investigated. The water vapor barrier property and the ultimate tensile strength (UTS) were improved significantly (p < 0.05) as the CA percentage increased from 0 to 10% (W/W). At the level of 15% (W/W) CMC, the starch films showed the lowest WVP values (2.34 × 10⁻⁷ g Pa⁻¹ h⁻¹ m⁻¹) and UTS increased from 6.57 MPa for the film without CMC to 16.11 MPa for that containing 20% CMC.     

Mechanical properties of fragrant screwpine fiber reinforced unsaturated polyester composite: Effect of fiber length,fiber treatment and water absorption

Fragrant screwpine fiber reinforced unsaturated polyester composites (FSFRUPC) were subjected to water immersion tests in order to examine the effect of water absorption on the mechanical properties. FSFRUP composite specimen containing 30 % fiber volume fraction with fiber length of 3 mm and 9 mm was considered in this study. Water absorption test was performed by immersing specimen in sea, distilled and well water at room temperature under different time durations (24, 48, 72, 96, 120, 144, 168, 192, 216, 240 hours). The tensile, flexural and impact properties of the water absorption specimen were appraised and compared with those of the dry composite specimen as per the ASTM standard. The tensile, flexural and impact properties of FSFRUPC specimen were found to decrease with the increase in the percentage of moisture uptake. The percentage of moisture uptake of composite was reduced after alkali treatment with 3 % NaoH for 3 hours. In moisture absorption test, the lowest diffusion coefficient, D (6.62513×10^-13 m²/s) and swelling rate parameter, K _sr (6.341×10^-3 h^-1) were obtained through the specimen immersed in sea water. The chemical composition, elemental composition of fiber and surface morphology of the FSFRUPC were analysed by using Fourier transform infrared spectroscopy (FTIR), Energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) respectively.     

Thermo-mechanical and morphological properties of short natural fiber reinforced poly (lactic acid) biocomposite: Effect of fiber treatment

Untreated oil palm empty fruit bunch (REFB), alkali treated EFB (AEFB), ultrasound treated EFB (UEFB) and simultaneous ultrasound-alkali treated EFB (UAEFB) short fibers were incorporated in poly(lactic acid) (PLA) for fabricating bio-composites. The REFB fiber-PLA (REPC) and treated EFB (TEFB) fiber-PLA (TEPC) composites were prepared and characterized. Glass transition temperature, crystal melting temperature, decomposition temperature, melt flow index, density and mechanical properties (tensile strength, tensile modulus and impact strength) of TEPC are found to be higher than those of REPC. The observed crystallization temperature of TEPC is lower than that of REPC. Among all samples, TEPC prepared from UAEFB fiber shows better performances than other samples fabricated by REFB and AEFB fibers. Scanning electron microscopy, Fourier transform infrared spectroscopy and XRD analyses well support all the observed results.     

Effects of pressure treatment of hydrated oat,finger millet and sorghum flours on the quality and nutritional properties of composite wheat breads

Breadmaking achievement using grains alternative to wheat and rye is a challenging task for cereal technologists, since most of the available innovative breads are characterised by poor crumb and crust characteristics, slight flavour and fast staling. To improve texture, mouth-feel, acceptability and shelf-life of breads prepared by using minor and/or under-utilised cereals, gluten and/or polymeric substances that mimic the viscoelastic properties of gluten, are required. Recent studies reported that high hydrostatic pressure (HP) treatment may represent an efficient non-thermal technique to promote the dough structure formation of composite cereal matrices. In the present study the effects of HP on the techno-functional and nutritional properties of oat-, millet-, and sorghum- based breads were evaluated compared to their unpressured- and gluten-added conventionally made counterparts. HP-treated (350 MPa, 10 min) wheat, oat, millet and sorghum batters were added to the bread recipe, replacing 50%, 60% and 40% of untreated wheat flour, respectively. Data from bread analyses revealed non significant physico-chemical impairment, and superior nutritional and sensory profiles in most quality features when HP treatment was applied to dough batters, compared with conventional/gluten-added samples. Specifically, HP breads deserved better sensory scores and exhibited higher antiradical activities despite a reduction in specific volume (wheat and oat) and faster staling kinetics (millet and sorghum) that were explicit in some composite samples.     

Solvent crystallization of palm based dihydroxystearic acid with isopropyl alcohol: Effects of solvent quantity and concentration on particle size distribution, crystal habit and morphology, and resultant crystal purity

Crude dihydroxystearic acid was prepared from palm based oleic acid and was then solvent purified with isopropyl alcohol in a custom fabricated simultaneous batch crystallizer unit. The crystallized dihydroxystearic acid was a functional ingredient that acted as multipurpose intermediate for synthesis of various fine chemicals, cosmetics and personal care products. The effects of solvent quantity and concentration on particle size distribution, crystal habit and morphology, and resultant crystal purity were studied. The crystals were purer but smaller and the span of the distribution curve was wider at higher solvent quantity and concentration. Through scanning electron microscopy and X-ray diffraction, it was observed that the crystals agglomerated into plate-like (flaky) habit with triclinic crystal structure. Solvent crystallization with 80% IPA at 20 °C and solute:solvent ratio of 1.0:1.0 was the most optimized and efficient, producing β-DHSA crystals that has high resistance against fat exudation during vacuum filtration process.     

Characterization of depolymerized residues from extremely low acid hydrolysis (ELA) of sugarcane bagasse cellulose: Effects of degree of polymerization, crystallinity and crystallite size on thermal decomposition

Sugarcane bagasse cellulose was subjected to the extremely low acid (ELA) hydrolysis in 0.07% H₂SO₄ at 190, 210 and 225 °C for various times. The cellulose residues from this process were characterized by TGA, XRD, GPC, FTIR and SEM. A kinetic study of thermal decomposition of the residues was also carried out, using the ASTM and Kissinger methods. The thermal studies revealed that residues of cellulose hydrolyzed at 190, 210 and 225 °C for 80, 40 and 8 min have initial decomposition temperature and activation energy for the main decomposition step similar to those of Avicel PH-101. XRD studies confirmed this finding by showing that these cellulose residues are similar to Avicel in crystallinity index and crystallite size in relation to the 110 and 200 planes. FTIR spectra revealed no significant changes in the cellulose chemical structure and analysis of SEM micrographs demonstrated that the particle size of the cellulose residues hydrolyzed at 190 and 210 °C were similar to that of Avicel.