Starch Foams Research Articles

Starch Foam Expansion in a Closed Mold

Processes with thermal treatment of starch-based materials for biologically degradable packaging products are analyzed here. The paper describes experiments on thermal forming of potato starch-based water suspensions in a closed mold at elevated pressures and temperatures of walls heated up to 200 °C. The time course of temperatures and also the sample expansion were detected by a network of thermocouples and compared with the pressure recorded inside the mold. Evolution of temperature profiles enables the estimation of time courses of sample expansion. Experiments with marking particles show that the crust sticks to the heater walls and only the sample core expands. Temperatures and pressures are closely related during expansion and the free water evaporation stage. Experiments confirm that temperatures are more or less uniform in the longitudinal direction and that the time profiles of temperature and pressure are characterized by peaks corresponding to perforation and recovery of foamed structure.

Physicochemical characteristics of phosphorylated cross-linked starch produced by reactive supercritical fluid extrusion

Cross-linking of starch blends by phosphorylation using reactive supercritical fluid extrusion was investigated. A starch blend was mixed with 9% (starch basis) sodium trimetaphosphate and extruded at 60–70 °C with 0.1 M or 0.2 M NaOH solution and 0–1.5% (dry feed) supercritical carbon dioxide (SC-CO2). Physicochemical and morphological characteristics of extruded starch phosphates were evaluated and compared with unextruded and extruded starch controls. Degree of substitution (DS = 0.05) and incorporated phosphorus content (P = 0.92%) was highest in the starch phosphates produced with 0.2 M NaOH, indicating the highest level of cross-linking. Cross-linking of starch at highest reaction pH was also evidenced by its lowest water solubility and highest proportion of distarch monophosphate investigated by 31P NMR. Introduction of phosphate cross-links into the starch restricted the molecular structure mobility, leading to an increase in the gelatinization temperature (by up to 7 °C). SC-CO2-based expansion provided light weight and non-porous skin starch foams with excellent water resistance which would be desirable properties for their utilization as a biodegradable material.

Starch-lignin foams

Although starch foams are well known as biodegradable alternatives to foamed polystyrene, starch-lignin foams have not previously been reported. Lignin is an abundant byproduct of paper manufacture usually burned as fuel for lack of higher-value uses. We have prepared novel starch-kraft lignin foams with a known technique similar to compression mold- ing. Replacing 20% of the starch with lignin has no deleterious effect on density or morphology as indicated by scanning electron microscopy: a thin outer layer of approximately 100 μm encloses a region of cellular structure containing 100-200 μm voids, with the major internal region of the foam consisting of large voids of up to 1 mm in size. Powder X-ray diffraction shows residual structure in both starch and starch-lignin foams. Differential scanning calorimetry displays endothermic transitions in the starch foam but not in the starch-lignin foam, indicating that lignin stabilizes the residual starch structure. Lignin decreases water absorption; diffusion constants for the starch and starch-lignin foams are 2.68·10 -6 and 0.80·10 -6 cm 2 /sec, respectively. The flexural strength of the starch-lignin foam is similar to that of foamed polystyrene, the strain at maximum stress is smaller, and the modulus of elasticity is larger.

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

AbstractThe 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

Dimensional changes of starch microcellular foam during the exchange of water with ethanol and subsequent drying

Starch microcellular foams (SMCF) containing pores in the micron size range may be prepared by pore-preserving drying processes, developing highly porous, high specific surface area materials useful for applications such as opacifying pigments or as adsorbent materials. The objective of this research was to understand how the exchange of water with ethanol, used as a pore preserving step, affected the dimensional properties of the starch material during and after processing. SMCF were prepared from molded aquagels of cooked corn starch that were subjected to ethanol exchanges with different time intervals (6, 12, or 48 hrs) and number of exchanges (1, 2, or 3) and then air dried. To study the transformation of water-swollen starch into precipitated starch foam in ethanol, the volume of the starch material was measured in the wet state after each exchange and after final air drying. As water is replaced by ethanol, the starch material contracts, with the greatest contraction during the first ethanol exchange. The amount of contraction during air drying decreased with decreased starch water content just before air drying, presumably due to less pore collapse of the stiffer cell walls on drying. Interestingly, the minimum density of 0.37 g/cc SMCF was for the 12 hour exchange time, not the longest exchange time. Evidence of a skin-core morphology included SEM images as well as dimensional instability data on dried samples. The results indicate that SMCF of low density with fewer tendencies to deform during drying does not necessarily require extremely long exchange times.

WATER ABSORPTION AND MECHANICAL PROPERTIES OF STARCH FOAM TRAYS IMPREGNATED WITH STARCH ACETATE

Summary Starch foam trays were developed as an alternative to the single-use expanded polystyrene (EPS) trays used for food products. The foam trays were prepared by heating a mixture composed of cassava starch, cellulose fibres and calcium carbonate inside a metallic mould. Starch-based foam trays are brittle and sensitive to moisture and thus further treatments are necessary to improve their mechanical properties and water resistance. To minimize water absorption, the foam trays were impregnated with starch acetate dissolved in chloroform at concentrations of 1:3 (g.mL –1 ), 1:5 (g.mL –1 ) and 1:10 (g.mL –1 ). The impregnation was carried out at atmospheric pressure and also by applying a vacuum pulse. The use of vacuum pulses decreased the water absorption of the impregnated foam trays by about 66%. On the other hand, there was no significant improvement in the mechanical properties of the impregnated trays. This work demonstrates that impregnation of porous samples with starch acetate is an alternative to decrease their water absorption.

Structure and Compression Behavior of Macro-composite Starch Foams

Using a method known as regular packing and stacking (RPS) technology, starch foams made by extrusion foaming of wheat flour can be converted by self-adhesion to produce bulk foams of any required sizes for much more broad applications. These block foams are reinforced by a network of the bonding interfaces and hence can be regarded as macrocomposites. The influence of the reinforcing interfaces on compression behavior of the RPS blocks was investigated by mechanical testing of foams with different geometry of the interface network and interface thickness. It is demonstrated that the interface network of the block foams can be designed to manipulate the macrostructure and compression behavior of the foam for protective packaging.

Fluorocarbon Barriers on Starch Foam Tray Surfaces Through SF6 Cold Plasma Treatment

Starch foam trays were produced using a laboratory model-baking machine. Surfaces of the trays were treated with SF6 plasma to create fluorine-rich layers on the surfaces. RF power, gas pressure and reaction time were varied to evaluate the effects of each parameter on fluorination of surfaces. The fluorine concentrations of treated sample surfaces ranged from 43.6% to 57.9%. For reaction time dependence, the ratio of oxygen to carbon was decreased since hydroxyl groups might be replaced by fluoro-compounds. Gas pressure and RF power affected fluorination mechanism, which resulted in different shapes of carbon and fluorine ESCA high resolution spectra. Plasma-treated samples have higher contact angles and less uptakes of liquid and vapor water. AFM showed different morphology of untreated and SF6 plasma-treated surfaces.

Environmentally Compatible Foamed Articles Based on Potato Starch, Corn Fiber, and Poly(Vinyl Alcohol)

Potato starch foam trays based on blends of poly(vinyl alcohol) and corn fibers (CFs), co-product of the corn-wheat wet-milling process, are prepared by baking the blended mixtures in a preheated mold. Materials are evaluated for processing parameters, foam strength, flexibility, and water resistance as a function of fibers content. Addition of CF in formulations improved not only moisture resistance of foam, but has a potential to lower the overall cost of the foamed materials substantially. Interestingly, addition of up to 45% fiber in formulations was possible without compromising the foaming process. Degradability is evaluated both in compost than simulating a disposal in the environment (soil burying and soil surface). Trays are biodegraded within 30—60 days in compost and soil. Particularly, trays containing starch and fiber degraded at much faster rates than trays prepared using starch without natural fillers.

Development of cross‐linked starch microcellular foam by solvent exchange and reactive supercritical fluid extrusion

AbstractStarch microcellular foams (SMCFs) are prepared by pore preserving drying or formation processes and contain pores in the micron size range. SMCFs have high specific surface area and are useful for applications such as opacifying pigments or as adsorbent materials. The objective of this research was to determine how the processing conditions and use of a crosslinking agent would affect the foam structure and properties. SMCFs (crosslinked and uncrosslinked) were prepared from molded aquagels and carbon dioxide extrusion processes separately and then solvent exchanged. Extruded samples showed macroscopic pores whereas samples from aquagels showed a much finer micropore structure. Aquagel‐based SMCF samples had lower density and higher brightness than did extruded samples. The starch foams with micropore structure had low density and high brightness. The solvent exchange process was the most important variable in generating a microcellular structure. Micropores and not macropores contributed to increased brightness of these materials. The brightness and density of the foams were found to be linearly related. Crosslinking with epichlorohydrin imparted significant water resistance to the extruded samples as evidenced in lower water swelling and higher contact angles. Equilibrium moisture content was correlated with the microporous structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Evaluation of ingredient effects on extruded starch-based foams using a supersaturated split-plot design

The aim of this study was to use a supersaturated split-plot design to identify the significant effects of ten ingredients, each at two levels, and two levels of screw speed on selected properties of starch-based packaging foams. Supersaturated designs are special types of fractional factorial designs that allow for evaluating many factors with a minimal amount of experimental material. Rice starch foams were prepared with a twin-screw extruder. The ingredients used were α-cellulose (fiber), potato starch, poly(lactic acid), polystyrene, glycerol, sodium chloride, talc, sodium bicarbonate, citric acid and moisture content of the feed. The properties studied were radial expansion ratio, unit density, bulk spring index, bulk compressibility and Young's modulus. The results showed that the ingredients identified to have significant effects on the properties were the high levels of talc, citric acid, moisture content and the low level of fiber. Low screw speed was found to have greater effect on the properties of the foams than did the high screw speed. It was concluded that the supersaturated split-plot design was successful in identifying the significant ingredients and screw speed that should be used to further investigate the extrusion of starch-based packaging foams.

Biomimetic Foams of High Mechanical Performance Based on Nanostructured Cell Walls Reinforced by Native Cellulose Nanofibrils

A bioinspired foam in which cellulose nanofibrils are used to reinforce cell walls (ca. 3 µm) is presented. The nanocomposite foams are prepared by a lyophilization technique and show composite structure at the cell-wall scale. The nanocellulosic network shows remarkable mechanical performance, expressed in much-improved modulus and yield strength compared with the neat starch foam.

Extrusion of starch‐based loose‐fill packaging foams: effects of temperature, moisture and talc on physical properties

AbstractStarch‐based loose‐fill packaging foams were made in a single‐screw laboratory‐scale extruder. Corn starch was blended with polystyrene in the ratio of 70 : 30 and extruded into foams using talc and polycarbonate as additives. Extrusions were carried out at moisture contents of 16, 18 and 20% (dry basis), and at barrel temperatures of 140 and 160°C. The influences of extrusion temperature, moisture content of starch, talc and polycarbonate on the radial expansion and other selected physical properties of starch foams were investigated. The effects of moisture and talc contents on the radial expansion of foams were found to be critical, while the role of temperature was close to significant. The expansion ratio increased when the moisture content was increased from 16 to 18%, and then decreased when moisture content was increased to 20%. In general, the expansion ratios of foams were higher at 160°C as compared to 140°C. Although polycarbonate mixed well with the starch–polystyrene melt, it was not effective as a structural and anti‐shrinking agent, and it did not contribute to the radial expansion. In general, the bulk densities and unit densities of the starch foams decreased as the moisture content and extrusion temperature increased. Scanning electron microscope images showed that the addition of talc yielded foams with smaller‐sized cells, with less expansion of the foam melt, and thus a higher density. X‐ray diffractograms revealed that the crystallinity of starch foams increased post‐extrusion, and there was adequate dispersion of the starch and polystyrene polymers to make the foam water‐resistant. Copyright © 2008 John Wiley & Sons, Ltd.

Properties of Starch Based Foams Made by Thermal Pressure Forming

Packaging materials based on expanded polystyrene can be substituted by biodegradable foam, manufactured by direct or indirect electrical heating of a potato starch suspension in a closed mold. This paper deals with an experimental evaluation of selected properties of potato starch and starch foam related to this technology: density, specific heat capacity and specific electrical conductivity of a water suspension of potato starch within the temperature range up to 100 °C, and mass fraction from 5 to 65 %. The electric conductivity and heat capacity changes were observed during direct ohmic heating of a starch suspension between electrodes in a closed cell (feeding voltage 100 V, frequency 50 Hz). Specific electric conductivity increases with temperature, with the exception of the gelatinization region at 60 to 70 °C, and decreases with increasing concentration of starch (the temperature and concentration dependencies were approximated using the Lorentz equation). Direct ohmic heating is restricted by a significant decrease in effective electrical conductivity above a temperature of 100 °C, when evaporated steam worsens the contact with the electrodes. Experiments show that when direct ohmic heating is not combined with indirect contact heating, only 20 % of the water can be evaporated from manufactured samples and the starch foam is not fully formed. This is manifested by only a slight expansion of the heated sample. Only the indirect contact heating from the walls of the mold, with the wall temperature above 180 °C, forms a fixed porous structure (expansion of about 300 %) and a crust, ensuring suitable mechanical and thermal insulation properties of the manufactured product. The effective thermal conductivity of the foamed product (sandwich plates with a porous core and a compact crust) was determined by the heated wire method, while the porosity of the foam and the thickness of the crust were evaluated by image analysis of colored cross sections of manufactured samples. While the porosity is almost constant, the thickness of the crust is approximately proportional to the thickness of the plate.

Tapioca Starch-poly (lactic acid)-based Nanocomposite Foams as Affected by Type of Nanoclay

Abstract Tapioca starch (TS), poly (lactic acid) (PLA), and clay nanocomposite foams, with three clays (Cloisite 30B, Na+, and 20A), were prepared by melt-intercalation method. The structural, thermal, physical and mechanical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Instron universal testing machine, respectively. XRD results indicated that the intercalation of TS/PLA into the nanoclay layers occurred for all three clays. The extents of intercalation depended on the types of clay and were exhibited in the sequence of Cloisite 30B>Na+ > 20A. At the same time, a mixture of intercalation and tactoid phenomena was observed for the TS/PLA/Cloisite Na+ nanocomposite. SEM results indicated a decrease in cell size of the TS/PLA foam matrix with the addition of nanoclay and cells had hexagonal and pentagonal shapes. Melting temperature (Tm) decreased with the addition of clays into TS/PLA matrix. Expansion ratios of the nanocomposites were significantly different (p<0.05) from each other. TS/PLA/Cloisite Na+ nanocomposite had the highest expansion ratio of 20.9 compared to its TS/PLA/Cloisite 20A (9.65) and TS/PLA/Cloisite 30B counterparts (8.23). Addition of Cloisite Na+ resulted in the lowest unit density of 0.046 kg/m3, while no significant differences in unit density were observed for the foams with addition of Cloisite 30B and Cloisite 20A. Bulk spring index (BSI) was influenced significantly (p<0.05) with the addition of nanoclays into the TS/PLA matrix. TS/PLA/Cloisite Na+ nanocomposite had the lowest BSI of 0.936. The bulk compressibility was decreased from 14.1MPa for pure tapioca starch foam to 4.45MPa with the addition of PLA. The nanocomposite with Cloisite 30B showed the highest value of 17.4MPa, followed by those with Cloisite 20A (10.4MPa), and Cloisite Na+ (6.47MPa).

Biodegradation of low‐density polyethylene/thermoplastic starch foams before and after electron beam irradiation

AbstractFoamy low‐density polyethylene/plasticized starch (LDPE/PLST) blends at different compositions were produced in the presence of azodicarbonamide (ACA) compound as foaming agent. The LDPE/PLST blends before and after electron beam irradiation were investigated in terms of mechanical properties, bulk density, and structure morphology. Moreover, the biodegradability of these materials was evaluated by the soil burial test for 2 months, in which the buried sheets were also examined by scanning electron microscopy (SEM). The results showed that the increase of PLST content from 24 to 30% was accompanied by a decrease in the yield and break stresses of 10 and 20% for the unirradiated blends without the foaming agent, respectively. Further decrease in these mechanical parameters was observed after the foaming process. The bulk density, void fraction, cell size measurements as well as the examination by SEM illustrate clearly the cell growth of the foam structure. The soil burial test and SEM micrographs indicate the growth of microorganisms overall the blend sheets and that the blend was completely damaged after two months of burying. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

X-ray tomography study of the cellular structure of extruded starches and its relations with expansion phenomenon and foam mechanical properties

The cellular structure of extruded starch foams, with different amylose content (0–70%) has been determined by X-ray tomography (10 and 40 μm), leading to highly contrasted 3D images. These foam structures were analysed using a 3D granulometric approach. Their cellular features were determined for relative density ( D ∗) values in the interval [0.11, 0.34]. Their mean cell size (MCS) and mean cell wall thickness (MWT) varied in the range [0.2, 5 mm] and [75, 630 μm], respectively, and were strongly correlated. For the same value of D ∗, the finest structures (MCS < 2 mm and MWT < 300 μm) were found the most resistant to rupture. These finest cellular structures were mainly obtained for larger moisture content (24%) during extrusion. The influence of the extrusion variables on the phenomena occurring at die expansion, such as nucleation, bubble growth and coalescence, was discussed. Finally, the influence of amylose content was attributed to elongational viscosity, in relation with the storage modulus in the rubbery domain.

Laboratory composting of extruded starch acetate and poly lactic acid blended foams

Composting of extruded foams made of starch acetate and poly lactic acid (PLA) with pre-conditioned yard waste was studied using a laboratory composting system. Extruded foams of high amylose starch were used as the control. Degradation was measured by analyzing the exhaust gases for carbon dioxide. There were significant differences in the amounts of carbon dioxide produced in the vessels containing foams of high amylose starch and foams of starch acetate blended with 20% or 30% PLA. The high amylose starch foams completely degraded within 15 days. The starch acetate foams with 0% PLA took longer, with evolution of carbon dioxide still measurable after 55 days. The rate of degradation was faster for foams with higher PLA contents. The starch acetate foams took even longer to degrade. The maximum time was found to be 130 days for the starch acetate foams.

Development and characterization of novel starch and alkyl ketene dimer microcellular foam particles

There is interest in replacing inorganic fillers in paper, coatings and plastics with renewable organic fillers to improve the economics, performance and environmental aspects of such products. Starch microcellular foam (SMCF) particles are promising materials in this regard. This research was undertaken to produce SMCF particles and characterize their morphology, optical properties and interaction with water. SMCF particles were produced using corn starch; which was solubilized in water. The foam structure was created by precipitating the starch using ethanol in a solvent exchange technique. The starch was also reacted with alkyl ketene dimer (AKD) wax at different levels in order to understand if the AKD could impart water resistance to the particles. Two methods were used to incorporate AKD: (1) the AKD was coated onto foam particles after foam formation, and (2) the AKD was blended with the starch before foam particle formation. Hexane extraction was used to purify a portion of each of the samples to determine if unreacted AKD existed with the starch matrix. Particles with porous structure and high brightness were developed for all combinations of starch and AKD. The brightness of the particles was significantly higher than that of the uncooked starch, presumably due to the development of a porous structure. For the AKD coated particles a minimum amount of AKD charged was needed to develop a high contact angle, low solubility, and low water retention value, higher levels of AKD in AKD coated particles did not further alter these properties. This indicates that the changes in properties with AKD level with coated particles is a surface phenomena. Starch AKD blends did not show any increased resistance to water relative to the particles with no AKD blended. This is due to the ethanol used in the precipitation process extracting the AKD, which was confirmed by elemental analysis. The particles, even with the 10% AKD coated or blended, lost their porous structure upon rewetting. Further work needs to be performed to more effectively hydrophobize the starch foams with AKD.

Effect of eggshell powder as nucleating agent on the structure, morphology and functional properties of normal corn starch foams

AbstractCorn starch and eggshell powder (with particle sizes of 4–5µm and 8–10µm) composite foams were prepared by extrusion. Effects of eggshell on the structure, morphology, physical properties (unit density and expansion ratio), mechanical properties (spring index and compressibility) and thermal behaviour (thermal transition and stability) of the foams were investigated. Foam cell size decreased and cell population increased with addition of eggshell into starch matrix. The foam unit density, expansion ratio and compressibility decreased significantly (p &lt; 0.05), while the spring index increased significantly (p &lt; 0.05) as the eggshell content increased from 0 to 6wt%. Further increasing eggshell content to 10wt% increased the unit density and compressibility and decreased the expansion ratio and spring index. The thermal transition and stability increased with the addition of eggshell. The optimum eggshell content was 6wt% and the smaller‐sized eggshell powder had a favourable effect on the functional properties of the foams. Copyright © 2006 John Wiley &amp; Sons, Ltd.