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.     

Effect of potassium persulfate on graft copolymerization and mechanical properties of cassava starch/natural rubber foams

The aim of this study was to improve the mechanical properties of thermoplastic starch foams prepared from cassava starch blended with natural rubber latex by reactive blending. Potassium persulfate was used as an initiator for graft copolymerization between the starch and natural rubber during baking. The starch–natural rubber graft copolymer (starch‐g‐NR copolymer) was successfully produced during both suspension and melt blending based on ¹H‐NMR and FTIR characterization. Natural rubber increased the flexural modulus of starch/natural rubber foams without potassium persulfate, thus indicating the compatibility of the blends. The starch‐g‐NR copolymer, acting as a compatibilizing agent, enhanced the impact strength of foams, but it did not improve the flexural modulus. This may be due to the potassium persulfate decreasing the molecular weight of the natural rubber. Relative humidity also played an important role on the mechanical properties. Foams became more ductile at higher relative humidities. Since foam density increased with an increasing natural rubber content, the specific impact strength was also considered. A soil burial test showed that the cassava starch foams and foams containing 15 pph of natural rubber were fully biodegraded within 8 and 18 weeks, respectively. The starch‐g‐NR copolymer delayed biodegradation of foams and foams containing high natural rubber content, i.e., 35 pph, showed a low ability to be biodegraded. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ultrahigh compressive strength and heat resistance of polystyrene/polyphenylene oxide foams of supercritical carbon dioxide foaming

Polystyrene (PS) foam materials are lightweight, but suffer from poor compressive strength and heat resistance, among other problems, which limit their application. Herein, a method for preparing PS foam with high compressive strength and high heat resistance using supercritical CO₂ is proposed. PS/polyphenylene oxide (PPO) blends were prepared using a corotating intermeshing twin-screw extruder. The results showed that PPO exhibited excellent molecular-level compatibility with PS, which substantially improved mechanical properties and heat resistance of PS. Foam samples of PS/PPO blends with the same expansion ratio were prepared via batch foaming experiments, and the compressive strength of different foams was determined at different temperatures. At room temperature, the compressive strength of the PS/PPO-30% foam increased by 173% compared with pure PS foam. As the testing temperature increased from 30 to 120°C, the compressive strength of pure PS foams decreased rapidly. Nevertheless, PS/PPO foams maintained high compressive strength at high temperatures.     

Effect of citric acid,PVOH, and starch ratio on the properties of cross-linked poly(vinyl alcohol)/starch adhesives

The properties of tapioca starch adhesives were improved by cross-linking and the cross-linked adhesive compared with pure tapioca starch and poly(vinyl alcohol) adhesives. The effect of starch ratio, type of PVOH, and adding citric acid were important factors on the cross-linked adhesives. Wood adhesives made from cross-linked PVOH/starch were prepared by PVOH and tapioca starch, using hexamethoxymethyl melamine (HMMM) and citric acid (CA) as a cross-linking agent and catalyst, respectively. The effect of CA, PVOH/starch ratio, and type of PVOH such as medium (M PVOH) and high molecular weight (H PVOH) were investigated. The condition of the cross-linking reaction was 175?°C for 15?min. The structural properties of cross-linked adhesive were investigated by FT-IR spectroscopy. The results were confirmed in terms of thermal properties with a differential scanning calorimeter (DSC) and the shear strength of the adhesive. The cross-linked adhesive resulted in the increase of T _g and showed good blend compatibility with all of the cross-linked adhesives. The adhesive strength significantly increased when using CA as a catalyst in the cross-linking reaction. The optimum contents of the cross-linked PVOH/starch adhesives were 1:1.8 for M PVOH and 1:0.5 for H PVOH.     

Preparation and characterization of kaolin/starch foam

The objective of this work was to study the effect of the kaolin content on the properties of starch foams. The kaolin/starch foams were made with kaolin contents that ranged from 0 to 15 m% by baking in a hot mold. The starch and kaolin/starch foams were stored at room temperature with a relative humidity (RH) of 55% for 7 days prior to testing. An increase in the kaolin content increased the foam density. The izod impact strength increased up to 1151.37 J/m² at the highest kaolin content (15 m%). The improvement was about five times the izod impact strength of pure starch foam. Moreover, the presence of any kaolin reduced the water absorption ability of the starch foam. Scanning electron microscopy revealed that kaolin increased the size of the starch foam cells and was itself well dispersed. Kaolin/starch foams showed a higher thermal stability than pure starch foam.     

Comparative study of physical properties of water‐blown rigid polyurethane foams extended with commercial soy flours

The use of renewable resources (mainly carbohydrates) in rigid polyurethane foam has been known to offer several advantages, such as increased strength, improved flame resistance, and enhanced biodegradability. Less attention has been directed to inexpensive protein‐based materials, such as defatted soy flour. The objectives of this study were to develop water‐blown rigid polyurethane foams, containing defatted soy flour, that have acceptable or improved physical properties which also lower the cost of the foam formulation and to compare the properties of developed foams extended with three kinds of commercial soy flour. Water‐blown low‐density rigid polyurethane foams were prepared with poly(ether polyol)s, polymeric isocyanates, defatted soy flour, water, a catalyst mixture, and a surfactant. Soy flour and the initial water content were varied from 0 to 40% and from 4.5 to 5.5% of the poly(ether polyol) content, respectively. A standard laboratory mixing procedure was followed for making foams using a high‐speed industrial mixer. After mixing, the mixture was poured into boxes and allowed to rise at ambient conditions. Foams were removed from boxes after 1 h and cured at room temperature for 24 h before measurement of the thermal conductivity and for 1 week before other property tests. Foam properties were determined according to ASTM procedures. Measurement of the physical properties (compressive strength, modulus, thermal conductivity, and dimensional stability under thermal and humid aging) of these foams showed that the addition of 10–20% of three kinds of soy flour imparted water‐blown rigid polyurethane foams with similar or improved strength, modulus, insulation, and dimensional stability. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 10–19, 2001     

Crosslinked glutinous rice starch filled polyvinyl alcohol films

The influence of glutinous rice starch (GRS) content and sodium hexametaphosphate (SHMP) in polyvinyl alcohol (PVOH) films were studied. The increase of GRS content (0–40 wt%) reduced the tensile strength (from 14.3 to 4.3 MPa) and elongation at break (from 183 to 52.5) of PVOH/GRS films. Nevertheless, the modulus of elasticity of PVOH/GRS films increased with GRS content, from 20.3 to 132.83 MPa. SHMP was used as a crosslinking agent, which improved more than 30% of tensile strength and modulus of elasticity of PVOH/GRS films. However, the elongation at break reduced after crosslinking process of the films. The crosslinked film showed better interaction between GRS and PVOH, as demonstrated by scanning electron microscopy. Conversely, the crosslinked films exhibited a lower swelling degree, but a higher gel content compared to uncrosslinked films. J. VINYL ADDIT. TECHNOL., 25:359–365, 2019. © 2019 Society of Plastics Engineers     

Effect of Attapulgite Clay on Biodegradability and Tensile Properties of Polyvinyl Alcohol/Corn Starch Blend Film

Polyvinyl alcohol (PVOH) with corn starch (CS) at 70/30 weight percent ratio were prepared by a solution casting method with the addition of attapulgite at a range of 0.0–1.0 grams. The aim of this study is to investigate the effect of attapulgite on biodegradability and tensile properties of PVOH/CS matrix. All the results were compared with the control sample (PVOH/CS). The presence of attapulgite had hindered the degradation process in enzymatic, soil, and compost burial. The water sorption content increased with increasing immersion time. The highest tensile strength and elongation at break were shown by the PVOH/CS with 0.2 g of attapulgite content.     

Poly(vinyl alcohol) composite films with high percent elongation prepared from amylose‐fatty ammonium salt inclusion complexes

Amylose inclusion complexes prepared from cationic fatty ammonium salts and jet‐cooked high amylose starch were combined with poly(vinyl alcohol) (PVOH) to form glycerol‐plasticized films. For the octadecylammonium salt complexes, elongation was significantly higher than the PVOH control when the amount of complex incorporated was from 20% to 70%. For the dodecyl‐ and hexadecylammonium salt complexes, elongation was significantly higher than PVOH films for 20% to 40% incorporation of cationic complex. Tensile strength declined with increasing levels of amylose‐ammonium salt complex, and surface hydrophobicity (contact angle) was significantly higher than PVOH films. Microscopy showed no phase separation or phase inversion, suggesting intimate mixing due to ionic interactions between cationic ammonium salt complexes and the hydroxyl groups of PVOH. The high elongations of these films and increased water contact angles are marketable advantages, along with the lower cost and increased biodegradability of the starch‐based component. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44110.     

Biodegradable foams of poly(lactic acid)/starch. I. Extrusion condition and cellular size distribution

Biodegradable foams derived from poly(lactic acid) (PLA) and starch were prepared by extrution using water as a blowing agent and talc as nucleation agent. Foam cellular size and size distribution was significantly affected by extrusion conditions (i.e., extruder temperature profiles, die diameters, and screw speed), and material compositions, (i.e., water concentration, PLA/starch ratio, and nucleation agent concentration). Foam with a relatively fine cellular size and uniform cellular size distribution was obtained under optimized conditions of PLA/starch ratio at 40/60, 15% water, 195°C temperature before the die, 3‐mm die nozzle diameter, 200‐rpm screw speed, and 2% talc. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Grafting starch xanthate with vinyl monomers and hydrogen peroxide in foam rubber production

Starch xanthate with degrees of substitution (D.S.) ranging from 0.12 to 0.56 reacted with vinyl monomers (acrolein, acrylamide, acrylic acid, acrylonitrile, methyl acrylate, or styrene) and hydrogen peroxide to form aqueous gels of starch–polyvinyl monomer graft copolymer. The same reactions conducted in a rubber latex medium resulted in a self-acidifying, self-heating, and self-foaming coagulation to give a foam rubber. Such products were formed from several synthetic latices (NBR, SBR, polyisoprene, and polychloroprene types) and natural rubber latex; noted for each were the effects of the D.S., of monomer and peroxide concentrations, and of starch:elastomer ratios. The dried foams were evaluated by standard strength tests. Foam rubber of acceptable extensibility and enhanced tensile strength (up to 110 psi) was obtained with 0.12–0.15 D.S. xanthate and with proper balance of vinyl monomer, peroxide, and starch:elastomer ratio. Resilience was fair to good, but compression set was rather poor compared to most foam rubbers of general use.     

Recycling of aluminum beverage cans for metallic foams manufacturing

This paper proposes recycling beverage cans (aluminum cans) to reduce the manufacturing cost of metallic foams, while it is discussed the effects of the alloying elements that reinforce the metallic matrix in resistance to compression, due mainly in part to the formation of the phase β-Al₆(FeMn). The manufacturing process used for the metallic foams was the Alporas modified, using an excess of 10 wt% pure calcium. This allowed not only to modify viscosity of the molten alloy but also to obtain important quantities of the reinforcing phase Al₄Ca. Once obtained, the foams were characterized using techniques including differential thermal analysis, optical microscopy, scanning electron microscopy, chemical analysis and compression tests. Additionally, Image J software was used to determine the percentage of porosity and the average pore size of the metallic foams. Foam density was calculated by immersion in water using the Archimedes principle. The results showed that foams manufactured with beverage cans have a homogeneous porous structure with an average porosity of 80%, an average pore size of 3 mm, a specific gravity 0.4 and a compressive strength of 22 MPa. These results are superior to those obtained in foams manufactured with pure aluminum as well as alloying foams such as Al–12Si–0.6Mg (A413), and Al–1Mg–0.6Si (A356).     

Effects of jackfruit waste flour on the properties of poly(vinyl alcohol) film

A series of biodegradable polymer films based on poly(vinyl alcohol) (PVOH) and jackfruit waste flour (JWF) was prepared in the presence of water and glycerol and cast by a solution casting method. The JWF was introduced as a promoter of biodegradability. The blended films were evaluated for their tensile properties, water absorption, water vapor transmission rate (WVTR), and degradation behavior under different environmental conditions such as natural weathering and natural soil. The tensile strength (1.7–6.4 MPa) and elongation at break (13–108%) of the PVOH/JWF films were lower than those of unfilled PVOH film (26MPa and 238%). However, the Young's modulus values (157–196 MPa) of the PVOH/JWF films were higher than that of unfilled PVOH film (137 MPa). The PVOH/JWF blended films showed higher water absorption and WVTR, which increased with increasing JWF content. Biodegradability tests revealed that the presence of JWF stimulated the degradation rate and caused the weight loss and reduction in tensile properties of the PVOH/JWF blended films. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Extrusion of humidity‐resistant starch foam sheets

An annular die is used to extrude cylindrical starch foams which are then sliced to yield foam sheets suitable for cushioning protection and insulation of shipping containers. Although starch foams, as a possible replacement of petroleum‐based foams, have been prepared in the past, their sensitivity to humidity remained a problem. Extensive research in the last few years has been focused on resolving the collapse of the foam at high humidity, improve the cushioning protection, and develop an economical foaming process. However, these issues are still problematic and need to be resolved before such biobased foams can gain entry into the marketplace. In this study, a Box–Behnken statistical design of experiment was used to optimize the properties of foams extruded with various additives. It was found that the density, cell structure, and the rate of water penetration of these foams were affected by the feed rates (e.g., foam composition) of the water, talc, and poly(hydroxy ether) (PHE). The use of PHE was found to be extremely effective to minimize the water sensitivity and it significantly increased the water penetration time of the foam sheets. These starch foams efficiently absorb impacts and recover its physical shape quickly to provide multiple cushion protection for moderately delicate products. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

The mechanical property and phase structures of wheat proteins/polyvinyl alcohol blends studied by high-resolution solid-state NMR

The phase structures of thermally processed wheat proteins (WP) and polyvinyl alcohol (PVOH) blends were studied by solid-state high-resolution NMR spectroscopy. The intermolecular interactions among the multi-component systems and the behavior of each component in the blends on scales of nanometers were examined. The mechanical properties of the blends were also measured and related to the phase structure studies. The results indicated that the polymer chains of WP could be homogeneously mobilized when thermally processed with glycerol and water as plasticisers, but the glycerol predominately associated with WP rather than PVOH in the blends. The intermolecular hydrogen bonding interactions between WP and PVOH caused some extent of miscibility in the system on scales of nanometers especially when the PVOH content was low. The tensile strength and modulus of the blends were improved as compared to WP. However, the intermolecular interactions were relatively weak and could not be further enhanced by increasing PVOH component in the blends. The particle miscible WP/PVOH blends contained plasticised WP and PVOH phases in conjunction with the miscible WP/PVOH phase. Increasing the PVOH content in the blends did not result in an increase of the percentage of the miscible phase and the blends tented to be immiscible while the elongation of the blends was reduced when increasing the PVOH content in the blends.     

Twin‐screw extrusion production and characterization of starch foam products for use in cushioning and insulation applications

Cylindrical starch foam shapes were produced on a small scale (～11–12 kg/hr) Werner Pfleiderer ZSK‐30 twin‐screw extrusion (TSE) process using water, which functions as a plasticizer as well as a blowing agent. The properties of the starch foams depend on the type of starch used (hydroxypropylated high amylose corn starch, 70% amylose), the amount of water and additives (poly(hydroxyamino ether)) (PHAE) used, and extrusion conditions such as temperature and the screw configuration. PHAE offers the adhesion and durability of epoxy resins with the flexibility and processibility of thermoplastic resins. PHAE was successful in imparting mechanical strength and toughness, cell integrity, weather and water resistance to the foam structure. The purpose of this work was to study the effects of the extrusion (melt) temperature, amount of water added and the screw configuration on the density of starch foams. The water externally added was varied from 3% to 12%, while the PHAE content was varied from 3% to 15% of the starch used (on a wet basis). The foaming was carried out at melt temperatures in the range from 85 to 145°C. A match of material properties with process engineering conditions was achieved to facilitate the control of expansion to a structure with valuable commercial properties. The effects of processing conditions on the foaming process were studied using a Werner Pfleiderer ZSK‐30 twin screw extruder. The optimum temperature, blowing agent content, and PHAE content were determined. The density of the cylindrical foam extrudates obtained was 22–25 kg/m³. The screw configuration, temperature and pressure profiles, and additives affected the morphology, expansion ratio (ER), resilience, and compressibility of the product. These results were then employed on an industrial scale (410–420 kg/hr) twin‐screw food extruder, a Wenger‐80, to manufacture foam sheets. The density of the foam sheets was 27–30 kg/m³. The cushioning and insulation properties were studied and are reported. POLYM. ENG. SCI., 46:438–451, 2006. © 2006 Society of Plastics Engineers     

Melt processing and characterization of polyvinyl alcohol and polyhydroxyalkanoate multilayer films

Multilayer films for food packaging applications composed of polyvinyl alcohol (PVOH) as the core layer and polyhydroxyalkanoate (PHA) as the outer skin layers were produced by the co‐extrusion process. Rheological properties of PVOH and PHA were performed and analyzed before co‐extruding into a cast film. Analysis of the rheological data indicated the processing temperatures and grades of the PVOH and PHA polymers that would produce similar viscosity and melt flow properties. To improve adhesion of the layers, PHA was grafted with maleic anhydride using a dicumyl peroxide initiator to provide a tie layer material, which improved the peel strength of the PHA and PVOH layers by over 2×. Oxygen transmission rate (OTR) testing showed that the multilayer sample provided an OTR of 27 cc/m²‐day at 0% relative humidity (RH) and rates of 41 and 52 cc/m²‐day at relative humidity values of 60% and 90% RH, respectively. This indicates significant barrier performance enhancement over monolayer PVOH that provided an OTR of 60 cc/m²‐day at 0% RH and 999 cc/m²‐day at 60% RH. Biodegradation testing of the films in the marine environment showed that both the unmodified and maleated PHA polymers displayed high levels of mineralization, whereas the PVOH material did not. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Investigation of Adhesion Performance of Aqueous Polymer Latex Modified by Polymeric Methylene Diisocyanate

Aqueous polymer isocyanate (API), which has good adhesive properties at ambient temperature and excellent resistance to warm/boiling water, and is friendly to the environment, is widely used in the timber-processing industry. To prepare high performance API, vinyl acetate homopolymer and copolymer emulsion were respectively cross-linked by three types of polymeric methylene diisocyanate (p-MDI). The potlife, curing time, bonding strength, and water resistance of API adhesives were tested with different cross-linkers and varying loadings (5–20%). Also the effect of polyvinyl alcohol (PVOH) content of aqueous vinyl latex on the performance of API was investigated. It was shown that the potlife and curing time of API were obviously influenced by the types of cross-linker and its loading. Correct loadings of p-MDI as crosslinker can remarkably improve the adhesive performance of aqueous polymer emulsion at ambient temperature. Excess cross-linker cannot maintain such an effect of strengthening and may decrease considerably the bond properties of API. The warm- and boiling-water resistance of API improved markedly with increasing cross-linker loading, where emulsifiable isocyanate gave better cross-linking performance, and p-MDI mixed with organic solvent was the secondbest. With the increase of PVOH content, the curing time of API increased, but no statistically apparent differences in the potlife of API were found. The bonding performance of API was improved as PVOH content increases, but excess PVOH also weakenes the warm- and boiling-water resistance of the joint.     

Properties of protective loose-fill foams

This study compared the performance of eight commercial starch and expanded polystyrene (EPS)-based loose-fill foam products. Density of starch-based foams is higher, by a factor of two to three times, than either EPS-based ones. Compressive stress of most starch-based foams did not differ significantly from 0.0893 MPa value for virgin EPS foam. EPS- and starch-based foams have predominantly a closed and open cellular structure, respectively. Resiliency or elastic recovery of starch-based foams had values between 69.5 and 71.25%, which is about 10% lower than virgin EPS foam. Friability of both starch- and EPS-based foams was between 2 and 6 wt %, but starch-based foams broke into a fine dust, whereas EPS-based foams broke into large fragments. After conditioning at 20, 50, and 80% r.h., 23°C and 50% r.h., 35°C, the water content for starch-based foams averaged 6.0, 9.5, 14, and 8.5 wt %, respectively. The mechanical properties of starch-based foams were more sensitive to changes in relative humidity and temperature than EPS-based foams, but the higher amount of absorbed moisture did not compromise its mechanical integrity. © 1998 John Wiley & Sons, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America. J Appl Polym Sci 67:1157–1176, 1998     

Biodegradable packaging foams of starch acetate blended with corn stalk fibers

Starch acetate–corn fiber foams were prepared by extrusion. Corn starch was acetylated (DS 2) to introduce thermoplastic properties. Corn stalks were treated with sodium hydroxide to remove the lignin and to obtain purified cellulose fibers. Starch acetate was blended with treated fiber at concentrations of 0, 2, 6, 10, and 14% (w/w) and extruded in a corotating twin‐screw extruder with 12 to 18% w/w ethanol content and 5% talc as a nucleating agent. The samples were extruded at 150°C and selected physical and mechanical properties were evaluated. Micrographic properties were analyzed using scanning electron microscopy to observe the interaction of fiber and starch. Fiber incorporation at the lower concentrations enhanced the physical properties of the foams. Fiber contents greater than 10% decreased expansion and increased density and shear strength. Good compatibility between starch and corn fiber was observed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2627–2633, 2004