Effect of Recycled Polyolefin Inclusion on the Properties of Polypropylene Filaments

Abstract

A series of polypropylene filaments containing a number of recycled polyolefins in varying concentrations are extruded in the absence and presence of a thermal stabilizer package. The physical and chemical properties of these filaments are then characterized to identify the effects of adding the recyclate. While the added recyclate affects the overall properties, there is a tolerance level up to which the changes may be accepted, and the magnitude of the overall effect depends on the physical and chemical properties of the recyclate.The need to increase the levels of recycling and reuse of polymers is a current concern, but despite research efforts to date [ 1,21,22], uses are limited to areas where properties are not critical. In areas where the products need' to be highly oriented, for example fibers, filaments and tapes, producers often introduce up to 10% by weight of their own process waste, since the demands of a high degree of chemical purity and physical order can be met by having a full knowledge of the recycled polymer being used. Commercially available recyclates have not been used for two reasons: first, if the history of a recycled polymer is not fully known, then the chemical purity and additive content cannot be guaranteed, and the presence of degradation products from oxidation and general polymer chain scission can adversely affect the properties of the derived filaments. Second, fibers and filaments used in textiles often undergo a coloration process at some stage, so the color of any recyclate becomes important. Due to environmental and economic pressures, however, polymer processors of technical textiles need to increase the levels of recycled polymer in their products. Some areas of technical textiles, for example geotextiles, where aesthetic properties are less important, would be an ideal outlet for recycled polymer, provided the derived filaments or tapes possess physical properties and durabilities comparable to those exhibited using virgin polymer only [28].In a recent study [11,12] of a laboratory-produced recycled polymer blended with virgin polymer for derived, oriented tapes, we have shown that there is an initial tolerance of up to 25% w/w recycled polymer before an unacceptable loss in tensile properties occurs. This increases to 75% w/w recycled polymer when an additional stabilizer is used. In this paper, we extend that earlier work to explore the effects of selected commercial recyclates on the physical and chemical properties of derived filaments. Experimental WorkRAw MATERIALS Five recycled polypropylene polymers (coded Ri to R5) were selected for this study. The physical properties of melt flow index (MH. g/10 min, 230°C, 2.16 kg). number-average molecular weight (Af~), weight-average molecular weight (M&dquo;.), and the polydispersity index (M&dquo;.lM&dquo;) of the recyclates and the virgin polymer (vPP) with which they were blended are given in Table I. M&dquo; M and Mn values were measured by gel permeation chromatography at RAPRA Technology, U.K. The virgin polymer was a...