Wood Flour: New Filler for the Rubber Processing Industry. IV. Cure Characteristics and Mechanical Properties of Natural Rubber Compounds Filled by Non-Modified or Corona Treated Wood Flour T. G. Vladkova, 1 P. D. Dineff, 2 D. N. Gospodinova, 2 I. Avramova 1 1 Department of Polymer Engineering, University of Chemical Technology and Metallurgy, Sofia, Bulgaria 2 Department of Electrical Apparatus and Technology, Technical University, Sofia, Bulgaria Received 9 April 2005; accepted 30 August 2005 DOI 10.1002/app.23730 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: It is presented here how some cure charac- teristics and mechanical properties of rubber compounds based on nonpolar rubber, natural rubber (NR), are affected by filling with conifer wood flour, both nonmodified or corona treated in air or in ammonia. The corona treatment was performed at room temperature and varied both: treat- ment duration and voltage to find out the maximal reinforc- ing effect of the modified wood flour. The discharge voltage was varied at 10, 12, and 15 kV to include both (1) the range of relative low voltages (lower than 10  12 kV in which the major active species arise from ionized and activated air oxygen and (2) the range of relative high voltages (12 kV and higher) in which the active species arise from simulta- neously ionized and activated air oxygen and nitrogen. The chemical composition of the nonmodified and corona- treated wood surface was controlled by X-ray photoelectron spectroscopy (XPS) analysis. The activity of the modified wood flour was evaluated by comparative measurement of some basic mechanical parameters of rubber compounds, filled at equal level by nonmodified or plasma-treated wood flour. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 651– 658, 2006 Key words: conifer wood flour; nonmodified and activated through corona treatment in air or in ammonia; XPS analy- sis; filled NR compounds; cure characteristics; mechanical properties; ageing resistance INTRODUCTION The wood is a renewable natural material and the waste wood is an important biomass resource. Many research groups are looking for ways to its utilization including new polymer composites development. There are a number of publications discussing possi- ble wood filler modifications aimed at improvement of some technological and exploitation properties of such composite materials. Surprisingly, there is scant information about rubber compounds filled by wood- based disperse or fibrous fillers, although they hide interesting potential applications. Utilization of wood floor, made by conventional grinding of amortized railway traverses, as a filler in thermosetting epoxy resin/rubber compounds for high quality traverses production has been described in ref. 1. Nagay and Erman 2 have investigated the reinforcing effect of a hybrid carbon black/mica filler in both acrylonitrile– butadiene rubber (NBR) and NBR/polyvinylchloride (PVC) compounds. The effect of the mica replacement by wood flour on the mechan- ical properties, swelling, and cure behavior of the corresponding composites has been discussed in this article. Ismail and Nurdin 3 studied the tensile proper- ties of oil palm wood flour/natural rubber composites and also performed scanning electron microscopy ob- servations of fracture surfaces of these composites. They have found that the tensile modulus increases with the increase of the oil palm wood flour concen- tration whereas the tensile strength and the elongation at break show an opposite trend. The improvement of the oil palm wood flour/rubber matrix interface inter- action by different bonding agents has been substan- tiated with scanning electron microscopy. But system- atic investigations on the effect of wood flour in rub- ber as well as in rubber/plastic compounds are missing. Our preliminary experiments showed the ex- cellent wood flour ability to mix with all widely used rubbers: natural rubber, isoprene rubber, styrene rub- ber, butadiene rubber, acrylonitrile– butadiene rubber, etc. It has been found that the nonmodified wood flour acts as nonactive filler to NBR and NBR/PVC com- pounds 4 and corona treatment in air under optimal Correspondence to: T. G. Vladkova (TGV@uctm.edu). Contract grant sponsor: National Science Fund of Bul- garia; contract grant number: 1301/03. Journal of Applied Polymer Science, Vol. 101, 651– 658 (2006) © 2006 Wiley Periodicals, Inc.