Physicomechanical and hydrophobic properties of starch foams extruded with different biodegradable polymers

Blends of hydroxypropylated high amylose starch and various functional aids listed below were extruded into foams using a twin‐screw extruder ZSK ‐ 30. In this study, the hydrophobic character and mechanical properties of starch foams were improved by using other biodegradable polymers, such as poly‐caprolactone (PCL), poly (butylene adipate‐co‐terephthalate) (PBAT), cellulose acetate (CA), methylated pectin (MP), and polyvinyl alcohol (PVA), and crosslinkers like glyoxal. The hydrophobic character was improved in terms of a reduction in steady state weight gain, and an increase in dimensional stability (reduction in loss of radial and longitudinal dimensions) on moisture sorption. At the same time, efforts were made to maximize the expansion ratios by reduction of unit densities. Formulations of these foams (in terms of additive content and other processing parameters) were optimized. Particular formulations with PVA, polyesters like PCL and PBAT, and glyoxal with PVA gave foams with unit densities lower than 25 kg/m³. The dimensional stability increased with an increase in the polyester content, but the density increased beyond an optimum polyester content, too. The loss in radial and longitudinal dimensions under steady state conditions was 12–20% with polyesters as compared to about 50–55% for control starch. Addition of these processing aids did decrease the water sensitivity of the starch foams. Foams with CA and methylated pectin, in the presence/absence of glyoxal, had marginally lower unit densities and slightly higher expansion ratios, as compared to those of control starch. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 58–68, 2006     

Processing and properties of thermoplastic starch and its blends with sodium alginate

Viscosity measurements were carried out on corn starch (CS) and CS–sodium alginate (SA) suspensions at low levels of SA [1 to 10% (w/w)], as a function of temperature. The addition of SA caused the granular CS gelatinization process to occur at a lower onset temperature. CS and CS–SA mixtures were extruded in single‐ and twin‐screw extruders, with 15% glycerol and different water contents. Processing of plasticized CS–SA mixtures required lower temperatures, which is consistent with the viscosity results. Homogeneous and flexible extrudates were obtained by processing in a twin‐screw extruder. Samples in the composition range between 0 and 10% (w/w) SA were examined using tensile tests as a function of water content. Mechanical properties were dependent on the water content and on the SA composition. A significant increase in the Young's modulus value was observed for the blend containing 1% SA. Dynamic mechanical analysis was carried out for CS and CS–SA blends. Two transitions were detected in the temperature range –80 to 150°C. Scanning electron microscopy was used to examine the morphology of the extruded samples. The surfaces of the films were homogeneous, which demonstrated that the CS granules in all samples were characteristically destructured under the conditions used in processing. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 412–420, 2001     

Foaming of EVA/starch blends: Characterization of the structure,physical properties,and biodegradability

Foams produced from blends of an ethylene‐vinyl acetate copolymer (EVA) with high VA (vinyl acetate) content (28%) and corn starch have been successfully fabricated using an improved compression molding technique. A detailed characterization of the structure and physical properties has been carried out. The results showed that the corn starch acts as filler for EVA, showing a good compatibility with the polyolefin. Different types of cellular structure (closed, partially interconnected, and fully interconnected) and cell sizes were obtained depending on the relative density and the amount of starch included in the composition. Besides, the addition of starch allows tailoring the physical properties of the composite foams. An increase in the starch content leads to an increase of the density, compressive strength, hardness, and thermal conductivity and a decrease of the elasticity. Finally, biodegradability tests showed how increases the biodegradation with the amount of starch in the foam, which reaches 60% at 100 days for the foam with 70% of starch. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Properties of starch‐based blend films using citric acid as additive. II

Starch/polyvinyl alcohol (PVA) blend films were prepared by using corn starch, polyvinyl alcohol (PVA), glycerol (GL), and citric acid (CA) as additives and glutaraldehyde (GLU) as crosslinking agent for the mixing process. The additives, drying temperature, and the influence of crosslinker of films on the properties of the films were investigated. The mechanical properties, tensile strength (TS), elongation at break (% E), degree of swelling (DS), and solubility (S) of starch/PVA blend film were examined adding GL and CA as additives. At all measurement results, except for DS, the film adding CA was better than GL because hydrogen bonding at the presence of CA with hydroxyl group and carboxyl group increased the inter/intramolecular interaction between starch, PVA, and additives. CA improves the properties of starch/PVA blend film compared with GL. TS, % E, DS, and S of film adding GLU as crosslinking agent were examined. With increasing GLU contents, TS increases but % E, DS, and S value of GL‐added and CA‐added films decrease. When the film was dried at low temperature, the physical properties of the films were clearly improved because the hydrogen bonding was activated at low temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2554–2560, 2006     

Effect of shear stress extrusion intensity on plasticized corn flour structure: Proteins role and distribution

Plasticized corn flour‐based materials were prepared by extrusion and injection molding. Extrusion of corn flour blends (75% wet basis (wb)—glycerol (5 or 10% wb)—water) was performed in a twin‐screw extruder with either one or three shearing zones. Native corn flour is mainly composed of corn starch granules surrounded by proteins layers. Therefore, the destructuration of corn flour by thermomechanical treatments was analyzed (i) by techniques essentially allowing to monitor corn starch amorphization (differential scanning calorimetry, X‐ray diffractometry, determination of water sorption isotherms, susceptibility to hydrolysis by amylolytic enzymes) (ii) and via proteins layers role and distribution observed by confocal scanning laser microscopy and comparing the susceptibility of corn starch to hydrolysis by amylolytic enzymes in the presence or not of a protease. Both corn starch granules amorphization and proteins dispersion and aggregation were more pronounced for materials extruded in a screw profile with three shearing zones. For materials extruded in a screw profile with one shearing zone, the amorphization of starch was higher in materials made with 5% wb glycerol, whereas the proteins dispersion and aggregation was more pronounced in materials made with 10% wb glycerol. A barrier role of proteins to hydrolysis of corn starch by amylolytic enzymes was demonstrated and discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Shrinkage and re‐expansion of extruded starch acetate foams

The effects of concentration of steam, heating time, pretreatment, and cooling conditions on the shrinkage and re‐expansion of extruded starch acetate foam were investigated. The re‐expansion ratio was determined from the degree by which the foam cells were moistened under the condition tested. The higher the concentration of steam used, the faster and greater the foam re‐expanded. Shrinkage was a result of the negative pressure resulting from cooling and condensation of steam or ethanol inside the foam and the unbalanced osmosis of steam transported out of the foam and air transported into the foam and the resistance of foam cell walls. Quenching re‐expanded foams led to significant shrinkage, especially for foams re‐expanded with highly concentrated steam. Shrinkage cannot be avoided even if the foam is kept at the same temperature it was expanded at the nozzle. Gradually reducing the degree of concentration of steam could reduce the shrinking tendency of the re‐expanded foam. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4264–4268, 2006     

Effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on thermal properties,morphology, and tensile properties of low‐density polyethylene (LDPE) and corn starch blends

The effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on the thermal properties, morphology, and tensile properties of blends of low‐density polyethylene (LDPE) and corn starch were studied with a differential scanning calorimeter (DSC), scanning electron microscope (SEM), and Instron Universal Testing Machine, respectively. Corn starch–LDPE blends with different starch content and with or without the addition of PE‐g‐MA were prepared with a lab‐scale twin‐screw extruder. The crystallization temperature of LDPE–corn starch–PE‐g‐MA blends was similar to that of pure LDPE but higher than that of LDPE–corn starch blends. The interfacial properties between corn starch and LDPE were improved after PE‐g‐MA addition, as evidenced by the structure morphology revealed by SEM. The tensile strength and elongation at break of corn starch–LDPE–PE‐g‐MA blends were greater than those of LDPE–corn starch blends, and their differences became more pronounced at higher starch contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2904–2911, 2003     

The influence of maltodextrins on the structure and properties of compression‐molded starch plastic sheets

Starch plastic sheets were prepared by compression molding of starch‐based plastic granulates. The granulates were prepared by extrusion processing of mixtures of granular potato starch and several maltodextrins (5% w/w) in the presence of glycerol and water as plasticizers and lecithin as melt flow accelerator. The materials were semicrystalline, containing B‐type, V_h‐type, and E_h‐type crystallinity. The properties were dependent on water content. For the materials, a brittle‐to‐ductile transition occurred at a water content in the range of 11–12%, which was in accordance with the observed glass transition temperature. The structural and mechanical properties were a function of starch composition and maltodextrin source as well as molding temperature. The amount of granular remnants and residual B‐type crystallinity decreased with increasing processing temperature. The amount of recrystallized single‐helical amylose increased with increasing temperature. At molding temperatures in the range of 180–200°C, a sharp decrease in starch molecular mass occurred. The influence of molding temperature was reflected in a sharp increase in elongation at molding temperature above 160°C and a gradual decrease in elastic modulus. The tensile strength showed an initial small increase up to 160°C and a sharp decrease at higher molding temperatures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2207–2219, 1999     

Grafting of vinyl acetate onto low density polyethylene—starch biodegradable films for printing and packaging applications

Starch‐based biodegradable low‐density polyethylene (LDPE) films were used for graft copolymerization of vinyl acetate with ceric ammonium nitrate (CAN) in aqueous acidic medium as redox initiator with nitric acid. The extent of grafting was examined by Fourier‐transform infrared (FTIR) spectroscopy, attenuated total reflectance (ATR) spectroscopy, X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The objective behind the grafting of vinyl acetate onto the LDPE–starch biodegradable films is to make these suitable for printing and packaging applications without affecting the biodegradability of the original films. Copyright © 2004 Society of Chemical Industry     

Preparation and characterization of starch/polycaprolactone blend

To make starch/polycaprolactone (PCL) blend with high miscibility, starch was chlorinated (starch‐Cl) by using methanesulfonylchloride (CH₃SO₂Cl) in dimethylformamide (DMF) prior to blending. Starch‐Cl/PCL blends were prepared by the mixing between starch‐Cl and PCL solutions under various conditions. To study the change of structure, thermal and physical characteristics of starch‐Cl/PCL blend, FTIR, DSC, SEM, and solvent resistance were measured. By blending starch‐Cl and PCL, a chemical reaction occurred partially in blend (FTIR result); thereby, the miscibility (DSC and SEM results) and solvent resistance were increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1716–1723, 2004     

Starch–poly(vinyl alcohol) foamed articles prepared by a baking process

Composite foam plates were prepared by baking a mixture of granular starch and aqueous poly(vinyl alcohol) (PVOH) solution inside a hot mold. Foam strength, flexibility, and water resistance were markedly improved by addition of 10–30% PVOH to starch batters. The improvement in strength at low humidity was greater for partially (88%) hydrolyzed PVOH while strength at higher humidities improved most with fully (98%) hydrolyzed PVOH. Foam flexibility increased with higher PVOH molecular weight. Scanning electron micrographs of the surface of the foams revealed a phase-separated morphology in which swollen starch granules were embedded in a matrix of PVOH. The starch component was gelatinized (melted) during baking while the PVOH component crystallized to a high degree during baking. Crosslinking agents such as Ca and Zr salts were added to starch batters to give further increases in water resistance. Respirometry studies in soil showed that the starch component of starch–PVOH foams biodegraded relatively rapidly (weeks) while the PVOH component degraded more slowly (months). Baked foams prepared from starch and PVOH have mechanical properties that are adequate for use as packaging containers over a wide range of humidity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2129–2140, 1998     

Blending of poly(lactic acid) and starches containing varying amylose content

Four dry corn starches with different amylose content were blended at 185°C with poly(lactic acid) (PLA) at various starch:PLA ratios using a lab‐scale twin‐screw extruder. Starch with 30% moisture content also was blended with PLA at a 1:1 ratio. Each extrudate was ground and dried. The powder was mixed with about 7.5% plasticizer, and injection molded (175°C) into test tensile bars. These were characterized for morphology, mechanical properties, and water absorption. Starch performed as a filler in the PLA continuous matrix phase, but the PLA phase became discontinuous as starch content increased beyond 60%. Tensile strength and elongation of the blends decreased as starch content increased, but no significant difference was observed among the four starches at the same ratio of starch:PLA. The rate and extent of water absorption of starch/PLA blends increased with increasing starch. Blends made with high‐amylose starches had lower water absorption than the blends with normal and waxy corn starches. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3639–3646, 2003     

Preparation and properties of polyhydroxybutyrate blended with different types of starch

This study examines the properties of polyhydroxybutyrate (PHB) when blended with two types of maize starch, Starch 1 (containing 70% amylose) and Starch 2 (containing 72% amylopectin). The PHB/starch blends were prepared by melt compounding at a ratio of 70/30 by weight and characterized in terms of their morphology, structure, thermal, rheological, and mechanical properties. The results show that starch granules act as a filler in PHB/starch blends and also act as a nucleating agent causing a very significant reduction in the size of the PHB spherulites. There were found to be significant improvements in thermal, rheological, and mechanical properties, and these were greater for blends containing Starch 1 than those containing Starch 2. These improvements are attributed to enhanced hydrogen bonding between PHB and Starch 1 with high‐amylose content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Processing and properties of an ethylene–vinyl acetate blend foam incorporating ethylene–vinyl acetate and polyurethane waste foams

Waste polyurethane foam (w‐PU) and waste ethylene–vinyl acetate foam (w‐EVA) were used as fillers for the production of an ethylene–vinyl acetate (EVA) blend foam. Two different foaming techniques (single‐stage and heat–chill processes) were used for this purpose. The waste foam concentration was varied up to 30 wt % of the original EVA. The physical, mechanical, and morphological properties of the filled foam were studied. The single‐stage process produced blend foams with a lower density and a greater cell size than the foams obtained by the heat–chill process. The density and compression strength of the blend foam increased as the percentage of w‐PU foam increased. However, for the w‐EVA/EVA blend foams, the addition of w‐EVA foam did not significantly affect the density or compression strength compared to the original EVA foams. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44708.     

Preparation and characterization of modified starch‐based plastic film reinforced with short pulp fiber. I. Structural properties

Native corn starch‐ and hydroxypropylated starch (HPS‐) based plastic films were prepared using the short pulp fiber as the reinforcement and the glycerol as the plasticizer. Starch (or HPS) films showed different X‐ray diffraction patterns with the A‐type of native corn starch powder. The crystallinity of films increased with pulp content, but decreased with glycerol content and degree of substitution by hydroxypropylation. Also, the intensity of peaks at 2θ = 15.3 and 17.3° decreased with glycerol content and degree of substitution. The water uptake of films as a function of the relative humidity decreased with pulp content and degree of substitution by hydroxypropylation, but increased with glycerol content. Differential scanning calorimetry (DSC) thermograms showed that the glass transition temperature of films decreased and the endothermic peaks at the melting temperature broadened due to the plasticizing effect and the decrease of the crystallinity, which were caused by the addition of glycerol and the hydroxypropylation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2100–2107, 2003     

玉米淀粉改性API胶研究

先对玉米淀粉酯化制成玉米淀粉乳液,然后再用玉米淀粉改性水性高分子异氰酸酯胶(API)。即在一定条件下与玉米淀粉,碳酸钙,多异氰酸酯(PAPI)和丁苯胶乳相混合,搅拌均匀,调制成玉米淀粉胶粘剂, 压制三层胶合板,其性能完全达到有关标准要求,并且制品无甲醛无毒害物质挥发,原料成本也很低,具有明显的社会环境效益和经济效益。     

Properties of poly(lactic acid) blends with various starches as affected by physical aging

Poly(lactic acid) (PLA) and starch are both biodegradable and renewable polymers derived from agricultural feedstock. A previous study showed that a small amount (0.5%) of methylenediphenyl diisocyanate (MDI) could enhance the mechanical properties of starch and PLA blends by improving the interfacial interaction. In this study, blends of PLA (1/1, w/w) and starch with or without MDI were evaluated for thermal and mechanical properties as well as morphology, as affected by physical aging when stored up to 12 months at 25 °C and 50% relative humidity. The blends were prepared by thermally blending PLA with wheat starch, corn starch, and/or high amylose corn starch, with or without MDI. All samples exhibited phenomena of physical aging. The samples with MDI aged more slowly, showing a slower reduction rate of excess enthalpy relaxation, than those without MDI. The mechanical properties decreased slowly as aging proceeded. Microstructure showed a reduced interaction between starch and PLA around the interface with aging. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3683–3689, 2003     

Extruded foams prepared from high amylose starch with sodium stearate to form amylose inclusion complexes*

Extruded starch foams were prepared from high amylose corn starch with and without sodium stearate and poly(vinyl alcohol) (PVOH) to determine how the formation of amylose–sodium stearate inclusion complexes and PVOH addition would affect foam properties. X‐ray diffraction and Differential Scanning Calorimetry (DSC) showed that amylose–sodium stearate inclusion complexes were formed by low temperature extrusion and did not dissociate during foam formation by a second extrusion at higher temperatures. In the absence of PVOH, water absorption, and foam shrinkage at 95% RH were decreased because of the hydrophobicity of the complex. PVOH addition increased both the expansion ratio and the shrinkage of the foam, although shrinkage at 95% RH was still less than that observed with uncomplexed amylose. The structural integrity and some tensile properties of stearate‐containing foams were improved by PVOH addition. These results provide the manufacturer of biodegradable starch foams with an inexpensive method for tailoring foam properties for specific end‐use applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43251.     

A comparative study on the mechanical and degradation properties of plant fibers reinforced polyethylene composites

Coir and abaca fiber‐reinforced linear low density polyethylene (LLDPE) composites (30 wt% fiber) were prepared by compression molding. Coir and abaca fibers were treated with methyl methacrylate (MMA) using ultraviolet radiation to improve the mechanical properties of the composites. Concentration of MMA and radiation dose was optimized. It was found that 30% MMA in methanol along with photoinitiator Darocur‐1173 (2%) and 15th pass of radiation rendered better performance. Chemically treated fiber‐reinforced specimens yielded better mechanical properties compared to the untreated composites, whereas coir fiber composites had better mechanical properties than abaca fiber reinforced ones. For the improvement of the properties, optimized coir (coir fiber treated with 30% MMA) and abaca (abaca fiber treated with 40% MMA) fibers were again treated with aqueous starch solution (2%–8%, w/w) for 2–7 min. Composites made of 3%‐starch‐treated coir fiber (5 min soaking time) showed the best mechanical properties than that of abaca‐fiber‐based composites. Water uptake and soil degradation tests of the composites were also performed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Grafting starch nanocrystals onto the surface of sisal fibers and consequent improvement of interfacial adhesion in sisal reinforced starch composite

Starch nanocrystals (SNCs) were obtained by the hydrolysis of waxy starch and used to improve the interfacial adhesion of a composite of sisal fibers and starch. Sisal fibers were first treated with acrylic acid (AA), and the modified fibers were then reacted with SNCs to form ester groups. The grafted fibers were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The FTIR and XPS results showed that the SNCs were successfully grafted onto the surface of SF-AA, and an ester linkage was formed during the reaction of AA with the SNCs. The SEM analysis showed that the SNCs were distributed over the fiber surface. Tensile tests and pull-out tests were also performed utilizing a two-parameter Weibull distribution analysis to study the effect of the grafted SNCs on the mechanical and interfacial properties. Compared to the untreated fibers, the interfacial shear strength of the grafted SNCs fibers increased by 79.3%. Therefore, the structural similarity between starch and the SNCs contributed towards their compatibility and improved interfacial properties, with the introduction of SNCs being used as an alternative material for fiber surface modification. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47202.