1. Introduction
Functionalization of polyolefines by melt grafting of unsaturated polar groups onto the polymer backbone by using organic peroxides as free radical initiators has received considerable attention in recent years [1±13]. Maleic anhydride (MAH) has been grafted onto polyolefins especially in order to improve their compatibility with polar thermoplastics (e. g. polyamides and polyesters) and to promote their adhesion to glass fibers in polymer composites (coupling agent, [14]). The grafting reaction of MAH onto molten polyethylene (PE) [1], polypropylene (PP) [2], and ethylene-propylene rubber (EPR) [3] has been previously studied by Gaylord et al. Melt functionalization of PE [4,5] and PP via MAH grafting [6,7] was the topic of very recent publications, too. In a series of works by Greco et al. [8±11] the melt grafting of dibutyl maleate (DBM) onto EPR has been studied. Melt functionalization of EPR by MAH grafting was also reported by Wu and Su [12]. The peroxide-initiated grafting of MAH is accompained by crosslinking for PEs [1,4,5], while degradation via chain scission is the dominant effect in the case of molten PP [2,6,7]. To the extent that saturated ethylene±propylene copolymers contain ethylene and propylene units in the chain, both crosslinking and degradation should occur in maelation with peroxides [8±12]. The present investigation was undertaken to study the peroxide-initiated grafting of MAH onto ethylene±propylene±diene terpolymer (EPDM). EPDM is an unsaturated polyolefinic rubber with wide application fields. EPDM is often used also in thermoplastics, e. g. for the impact modification of PP [15] and in recipes of thermoplastic dynamic vulcanizates [16]. However, about the maleation of EPDM in the molten (bulk) phase and about its further use in thermoplastics less information is available [13,17,18]. The objective of this work was to contribute to this topic by studying the effects of
the grafting recipe and processing conditions (temperature, time, chamber fullness and rotor speed), respectively. A further aim of this study was to clarify those conditions which result in a grafted rubber (EPDM-g-MAH) of low crosslinking degree (gel content). Note, that the latter is a very important aspect when modification of polyamides and linear polyesters is targeted.
2. Experimental
2.1. Materials
The EPDM used (Buna1 AP 447 of Bayer) was a high ethylene grade (contents of ethylene, propylene and ethylidenenorbornen: 74, 21 and 5 wt%, respectively). A commercial maleic anhydride (MAH, 99% purity) was used for grafting. As peroxide initiator 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane (Trigonox1 101 of Akzo Chemicals) was selected. All other chemicals and solvents, viz. toluene (99.5% purity), benzyl alcohol (99% purity), methanol (99.5% purity), potassium hydroxide (89% purity), phenolphthalein (99.8% purity) and acetone (99.9% purity) were used without further purification.
2.2. Melt grafting
Composition of the reaction recipe was typically as follows: 35±36 g of EPDM (constant), 0±10 wt% of MAH (variable), and 0±1.0 wt% of Trigonox 101 (variable). The components were mixed in an electrically heated W50EH mixing chamber (nominal volume: 50 ml; optimum mixing volume: 41.3 cm3) of a Brabender Plasticorder. All the reactants (EPDM, MAH and peroxide) were dry mixed together before their fast introduction into the preaheated mixing chamber. Usually the mixing rate (rotor speed) was 75 rpm, but for some experiments it was varied between 35 and 90 rpm.
(1 votes, average: 5.00 out of 5)