Extrusion of starch-based loose-fill packaging foams - ResearchGate

PACKAGING TECHNOLOGY AND SCIENCEPackag. Technol. Sci. 2008; 21: 171–183Published online 25 February 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/pts.809Extrusion of Starch-based Loose-fillPackaging Foams # : Effects of Temperature,Moisture and Talc on Physical PropertiesBy Heartwin Amaladhas Pushpadass, Govindarajan Suresh Babu,Robert W. Weber and Milford A. Hanna*Industrial Agricultural Products Center and Department of Biological Systems Engineering, University ofNebraska – Lincoln, Lincoln, NE, 68583-0730, USAStarch-based loose-fill packaging foams were made in a single-screw laboratoryscaleextruder. Corn starch was blended with polystyrene in the ratio of 70 : 30 andextruded into foams using talc and polycarbonate as additives. Extrusions werecarried out at moisture contents of 16, 18 and 20% (dry basis), and at barreltemperatures of 140 and 160ºC. The influences of extrusion temperature, moisturecontent of starch, talc and polycarbonate on the radial expansion and other selectedphysical properties of starch foams were investigated. The effects of moisture andtalc contents on the radial expansion of foams were found to be critical, while therole of temperature was close to significant. The expansion ratio increased when themoisture content was increased from 16 to 18%, and then decreased when moisturecontent was increased to 20%. In general, the expansion ratios of foams were higherat 160ºC as compared to 140ºC. Although polycarbonate mixed well with the starch–polystyrene melt, it was not effective as a structural and anti-shrinking agent, and itdid not contribute to the radial expansion. In general, the bulk densities and unitdensities of the starch foams decreased as the moisture content and extrusiontemperature increased. Scanning electron microscope images showed that theaddition of talc yielded foams with smaller-sized cells, with less expansion of thefoam melt, and thus a higher density. X-ray diffractograms revealed that thecrystallinity of starch foams increased post-extrusion, and there was adequatedispersion of the starch and polystyrene polymers to make the foam water-resistant.Copyright © 2008 John Wiley & Sons, Ltd.Received 28 March 2007; Revised 24 July 2007; Accepted 14 December 2007KEY WORDS: expansion ratio; extrusion; starch foams; single screw; talcINTRODUCTIONPlastic packaging foams are used extensively ascushioning materials to protect fragile productsagainst shock or vibration during shipping andhandling. These foams are characterized by lowbulk densities, good hydrophobicity and adequatemechanical strength. There is an ever-increasingdemand for these loose-fill packaging materials.Conventionally, these packaging foams are madefrom petroleum-based products. In the USA, alarge volume of packaging foams is made from* Correspondence to: Milford A. Hanna, Industrial Agricultural Products Center and Department of Biological SystemsEngineering, University of Nebraska – Lincoln, Lincoln, NE, 68583-0730, USA.E-mail: mhanna1@unl.edu#A contribution of the University of Nebraska Agricultural Research Division, Lincoln, NE. This study was conducted at theIndustrial Agricultural Products Center.Copyright © 2008 John Wiley & Sons, Ltd.

EXTRUSION OF STARCH FOAMSPackaging Technologyand ScienceRelative Intensity1000090008000700060005000400030002000100000 5 10 15 20 25 30 35 40Angle 2Figure 9. X-ray diffractograms of: (a) native corn starch;(b) PS; and (c) starch-PS foam.cabConcentration of CO2,%6.005.004.003.002.001.000.000 6 12 18 24 30 36Time, daysFigure 10. Aerobic biodegradation of starch–PS foamsextruded from starch containing (a) 16% moistureand (b) 18% moisture.abcrystalline regions were from PS. Therefore, fromthe loss of the characteristic starch pattern and thegain in crystallinity in the extruded foams, it wasconcluded that starch and PS formed a homogenousand well-grafted matrix during extrusion.This fact could be strengthened from the separatetests done for the water absorption and watersolubility indices of the foams, which indicatedthat the starch-based foams were highly waterresistant,making them suited for loose-fill packagingapplications. It is evident that the starch foamswere made hydrophobic due to the addition of PSand by the proper binding between the two polymers.These results vindicated the addition of 30%PS to starch to make the starch foam water-resistant.However, it would be interesting to knowhow far the PS content can be reduced withoutcompromising the hydrophobicity and otherdesired physical or mechanical properties of thefoams.BiodegradabilityThe generation of CO 2 from the compost is presentedin Figure 10. It can be seen that the CO 2emitted reached a peak value before starting todecrease, regardless of the (sample) extrusion conditions.At the end of 30 days, the CO 2 productionreached a plateau, suggesting that the foams haddecomposed biologically. Foams made from starchcontaining 16% moisture content had a minimumsurface area due to reduced radial expansion, andhence took longer to reach the peak degradationrate. At the end of composting, the foams had afibrous and crumbly texture, presumably consistingof only PS. Pure PS is supposed to have ahalf-life period of 400–1000 years. However, thestructural rigidity of PS was lost due to the transformationsinside the extruder. It is presumed thatthe PS remaining in the compost will degrademuch faster, owing to the increased surface area(due to extrusion expansion) to degradation, aswell as the loss of structural rigidity.CONCLUSIONSWater-resistant starch-based foams can be preparedby replacing 70% PS with a starch biopolymer.The specific independent variables selected toevaluate the foams in this study were chosen asa result of discussions of the most critical foamproperties during commercialization activities.The expansion ratio and densities of the starchfoams depended on the initial moisture content,extrusion temperature and talc content. However,the effects of moisture content and talc on theradial expansion and densities of the foams weredominant over extrusion temperatures. SEMimages showed an increase in cell size with theincrease in moisture content of starch. In contrast,Copyright © 2008 John Wiley & Sons, Ltd. 181 Packag. Technol. Sci. 2008; 21: 171–183DOI: 10.1002/pts

Packaging Technologyand Scienceupon the addition of talc, the radial expansiondecreased, and the density of the foams increased.In general, 18% moisture content and 1% talc at anextrusion temperature of 160ºC was found to beoptimum for obtaining the maximum radial expansionand desirable physical properties of the foams.Polycarbonate did not affect the radial expansionor the physical properties of the foams. Hence, theuse of polycarbonate as a structural and antishrinkingagent is not recommended in the extrusionof starch-based foams. The loss of the peaksof native starch and the formation of new crystallineregions in starch foams indicated the fusion ofstarch and PS in the extruded foams. The starchfoams are recommended for loose-fill packagingapplications due to their better biodegradability,hydrophobicity and comparable bulkdensity.ACKNOWLEDGEMENTSThe authors are grateful to Dr David Marx, professor,Statistics Department of University of Nebraska – Lincoln,for formulating the fractional composite statisticaldesign to reduce the number of extrusion trials. Thisresearch paper is a contribution of the University ofNebraska Agricultural Research Division, supported inpart by funds provided through the Hatch Act. Mentionof trade names, proprietary products or company namesis for presentation clarity and does not imply endorsementby the authors or the University of Nebraska.REFERENCES1. Miladinov VD, Hanna MA. Physical and molecularproperties of starch acetates extruded with waterand ethanol. Ind. Eng. Chem. Res. 1999; 38: 3892–3897.2. Fang Q, Hanna MA. Functional properties of polylacticacid starch-based loose-fill packaging foams.Cereal Chem. 2000; 77: 779–783.3. Bhatnagar S, Hanna MA. Physical, mechanical, andthermal properties of starch-based plastic foams.Trans. ASAE 1995; 38: 567–571.4. Hutchinson RJ, Siodlak GDE, Smith AC. Influenceof processing variables on the mechanical propertiesof extruded maize. J. Mater. Sci. 1987; 22: 3956–3962.5. Wang L, Shogren RL. Preparation and properties ofcorn starch-based loose-fill foams. In Proceedings ofthe 6th Annual Meeting of the Bio/EnvironmentallyDegradable Polymer Society, St. Paul, MN, 1997.H. A. PUSHPADASS ET AL.6. Cha J, Chung DS, Seib PA. Effects of extrusion temperatureand moisture content on mechanical propertiesof starch-based foams. Trans. ASAE 1999; 42:1765–1770.7. Cha J, Chung DS, Seib PA. Rheological propertiesof blend melts for starch-based foams in extrusionprocessing. Trans. ASAE 1999; 42: 1801–1807.8. Guan J, Fang Q, Hanna MA. Functional propertiesof extruded starch acetate blends. J. Polym. Environ.2004; 12: 57–63.9. Nabar Y, Narayan R, Schindler M. Twinscrewextrusion production and characterization ofstarch-foam products for use in cushioning andinsulation applications. Polym. Eng. Sci. 2006; 46:438–451.10. Bhatnagar S, Hanna MA. Starch-based plastic foamsfrom various starch sources. Cereal Chem. 1996; 73:601–604.11. Chinnaswamy R, Hanna MA. Macromolecular andfunctional properties of native and extrusion-cookedcorn starch. Cereal Chem. 1990; 67: 490–499.12. Bhatnagar S, Hanna MA. Extrusion processing conditionsfor amylose-lipid complexing. Cereal Chem.1994; 71: 587–593.13. Zhou J, Hanna MA. Effects of the properties ofblowing agents on the processing and performanceof extruded starch acetate. J. Appl. Polym. Sci. 2005;97: 1880–1890.14. Hwang MP, Hayakawa KI. Bulk densities of cookiesundergoing commercial baking process. J. Food Sci.1980; 45: 1400–1402, 1407.15. Bhatnagar S, Hanna MA. Effect of Lipids on PhysicochemicalProperties of Extruded Corn Starch. ASAE(now ASABE) Paper No. 916541. St. Joseph, MI,1991.16. ASTM D5338-98. Standard test method for determiningaerobic biodegradation of plastic materialsunder controlled composting conditions. In AnnualBook of ASTM Standards. American Society forTesting and Materials: Philadelphia, PA, 2007;Section 8.03: 114–119.17. McLean RA, Anderson VL. Applied Factorialand Fractional Designs. Marcel Dekker: New York,1984.18. SAS. Proprietary Software Release v. 9.1, SAS Institute:Cary, NC, 2005.19. Chinnaswamy R, Hanna MA. Optimum extrusioncookingconditions for maximum expansion of cornstarch. J. Food Sci. 1988; 53: 834–836, 840.20. Lin S, Huff HE, Hsieh F. Extrusion process parameters,sensory characteristics, and structural propertiesof a high moisture soy protein meat analog.J. Food Sci. 2002; 67: 1066–1072.21. Alvarez-Martinez L, Kondury KP, Harper JM. Ageneral model for expansion of extruded products.J. Food Sci. 1988; 53: 609–615.22. Faubion JM, Hoseney RC. High-temperature shorttimeextrusion cooking of wheat starch and flour. I.Effect of moisture and flour type on extrudateproperties. Cereal Chem. 1982; 59: 529–533.Copyright © 2008 John Wiley & Sons, Ltd. 182 Packag. Technol. Sci. 2008; 21: 171–183DOI: 10.1002/pts

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