COMPOSITES SCIENCE AND TECHNOLOGY
Composites Science and Technology 65 (2005) 173–181 www.elsevier.com/locate/compscitech
Polyethylene reinforced with keratin ﬁbers obtained from chicken feathersq Justin R. Barone *, Walter F. Schmidt
USDA/ARS/ANRI/EQL, Bldg. 012, Rm. 1-3, BARC-West, 10300 Baltimore Ave. Beltsville, MD 20705, USA Received 15 January 2004; received in revised form 22 June 2004; accepted 22 June 2004 Available online 24 August 2004
Abstract Polyethylene-based composites were prepared using keratin ﬁbers obtained from chicken feathers. Fibers of similar diameter but varying aspect ratio were mixed into low-density polyethylene (LDPE) using a Brabender mixing head. From uniaxial tensile testing, an elastic modulus and yield stress increase of the composite over the virgin polymer was observed over a wide range of ﬁber loading. Scanning electron microscopy revealed some interaction between the polymer and keratin feather ﬁber. In addition, the keratin ﬁber had a density lower than the LDPE used in this study resulting in composite materials of reduced density. The results obtained from mechanical testing are compared to theoretical predictions based on a simple composite material micromechanical model. Published by Elsevier Ltd. Keywords: A. Fibers; A. Polymer-matrix composites; A. Short-ﬁber composites; B. Mechanical properties; B. Microstructure
1. Introduction There has been recent interest in developing composites based on short-ﬁbers obtained from agricultural resources. These ﬁbers are usually of lower density than inorganic ﬁbers, environmentally-friendly, and relatively easy to obtain. It is anticipated that the ﬁbers would not contribute to the wear of polymer processing equipment and may not suﬀer from size reduction during processing, both of which occur when inorganic ﬁbers or ﬁllers are used. Although the absolute property increase when using organic ﬁbers is not anticipated to be nearly as high as when using inorganic ﬁbers, the speciﬁc proper-
q Mention of trade names or commercial products in this article is solely for the purpose of providing speciﬁc information and does not imply recommendation or endorsement by the US Department of Agriculture. * Corresponding author. Fax: +1 301 504 5992. E-mail address: email@example.com (J.R. Barone).
ties are anticipated to be high owing to the much lower density of the organic ﬁbers. In short-ﬁber reinforced polymer composites, the integrity of the ﬁber/matrix interface needs to be high for eﬃcient load transfer. Ideally, the molten polymer would spread over and adhere to the ﬁber, thus creating a strong adhesive bond. Inorganic ﬁbers like glass and cellulosic ﬁbers have hydrophilic surfaces that make them incompatible with hydrophobic polymers. Therefore, inorganic and cellulosic ﬁbers usually require chemical modiﬁcation to increase ﬁber/polymer interactions . The chemical modiﬁcation, known as a coupling agent, acts as a ‘‘bridge’’ between the inorganic ﬁber and the organic polymer matrix. The ‘‘bridge’’ must adhere or bond to the ﬁber and, in turn, strongly interact with the polymer. When using glass ﬁbers, the coupling agent has a hydrophilic side that is compatible with the ﬁber and a hydrophobic side that is compatible with the polymer. In glass ﬁbers, the coupling agent reacts with the surface of the glass forming covalent bonds. Without the coupling agent, there is simply adhesion of the polymer to the glass through weak bonding,
0266-3538/$ - see front matter. Published by Elsevier Ltd. doi:10.1016/j.compscitech.2004.06.011
J.R. Barone, W.F. Schmidt / Composites Science and Technology 65 (2005) 173–181
i.e., van der Waals or induction interactions. Organic ﬁbers may oﬀer the possibility of covalently bonding the matrix polymer to the ﬁber either directly or through a similar type of chemical ‘‘bridge’’ and the chemistry may be easier. Covalent bonds are much stronger than induction or van der Waals...
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