Materials Letters 15 ( 1992) 224-228 North-Holland Viscoelastic properties of short-sisal-fiber-filled low-density polyethylene composites: effect of fiber length and orientation Kuruvilla Joseph, Sabu Thomas ’ zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFED School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala 686 631, India and C. Pavithran Regional Research Laboratory, Council of Scientific and Industrial Research, Trivandrum 695 019, India Received 5 August 1992 The viscoelastic properties of low-density polyethylene filled with short sisal fibers have been studied. The influence of fiber orientation on the viscoelastic properties of the composites has been investigated and it is found that the longitudinally oriented fiber composites show the maximum value of storage and loss moduli, whereas transversely oriented fiber composites show the minimum. The viscoelastic properties are also strongly influenced by fiber length. 1. Introduction Several cellulosic products and wastes such as shell flour, wood flour and pulp have been used as fillers in thermoplastics primarily to achieve cost savings [ 11. However, over the past decade, cellulosic fillers of fibrous nature have been of great interest as they would give composites with improved mechanical properties compared to those containing non-fibrous fillers [ 2-41. Since the fiber-reinforced thermoplas- tic composite materials undergo various types of dy- namic stressing during service, the studies on the vis- coelastic properties of these materials are highly important. Several studies have been reported on the viscoelastic properties of fiber-reinforced polymer composites. Murthy and De [ 5,6] have reported on the mechanical and viscoelastic properties of short- fiber-reinforced rubber composites. Carvalho and Rosario Bretas [ 71 have investigated the correlation between interphase morphology and viscoelastic properties of thermoplastic-carbon-fiber compos- 1 Author whom correspondence should addressed. ites. Recently, Otaigbe [ 81 has reported on the viscoelastic properties of nylon 6-continuous-glass- fiber composites for four levels of fiber volume fraction. In the present paper attempts have been made to study the effect of fiber length and orientation on the viscoelastic properties of short-sisal-fiber-reinforced polyethylene composites. 2. Experimental procedures Sisal fibers (Agave - Veracruz) supplied by a local extraction unit were used in the present study. The average diameter of the fiber calculated from the fraction of fibers of different diameter in a sample, was about 190 pm. The tensile strength, modulus and failure strain of the fibers measured were 400-700 MPa, 9-20 GPa and 5- 14%, respectively. Low-den- sity polyethylene (LDPE, Indothene 16 MA 400) was obtained from M/S Indian Petrochemical Corpo- ration Ltd., Baroda. The properties of LDPE are given in table 1. 224 0167-577x/92/$05.00 0 1992 Elsevier Science Publishers B.V. All rights reserved.