Ethylene-propylene-diene terpolymer crosslinking

Thioureas mainly find use for the vulcanisation of CR, epichlorohydrin (ECO) and some ethylene propylene diene terpolymer (EPDM) compounds. They show high crosslinking activity, with usually adequate compound flow time before onset of the crosslinking. In EPDMs, the thioureas are used as activators for low activity third monomer types and, in the presence of calcium oxide desiccants, in free state vulcanisation of extrudates, etc. The use of thioureas can overcome the retardation caused by the desiccant. In this case some care must be taken otherwise overcompensation may occur. Thioureas are not used in food product applications and are a known health hazard, particularly for pregnant women. 

In order to improve the stability of polyacetylene, polyacetylene was blended with ethylene-propylene-diene terpolymer. Subsequently, the resulting EPDM/PA blend was crosslinked with y-radiation. Upon doping with iodine, the conductivity of the blend was found to be in the range 10-100 SI-1 cm-. It was found that the conductivity of the crosslinked blend decayed more slowly compared to that of either the uncrosslinked blend or homopolyacetylene. 

The objects of our investigations were four kinds of elastomers, of different structure and polarity, viz. cis-1,4-polybutadiene (BR)> butadiene-acrylonitrile copolymer (NBR), isobutylene-isoprene copolymers (IIR) and ethylene-propylene-diene terpolymer (EPT). They were mixed with plastomers low density polyethylene (PE] ), polystyrene (PS), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polycaproamide (PCA) and polyacrylonitrile (PAN) (Table 1). The concentration of the plastomers in the mixtures was changed in the range from 0 to 50 pph of the elastomer. The polymers were blended at temperature T = 423 K by means of the micromill of the Plasti--Corder apparatus. After 24 hours, crosslinking substances, dicurayl peroxide (DCP) or sulphur and diphenylguanidine (S, DPG), were added at room temperature. The composition of the mixtures is given in Table 2. 

LDPE in the amount of 15phr was blended with ethylene-propylene-diene terpolymer. The method of blend preparation, at the temperature of 145 °C, that is, well above melting point of the crystalline phase of polyethylene, was described in Ref [2]. To crosslink elastomer matrix 0.6phr... 

The mechanical properties of polymer nanocomposites are also influenced by the chemical treatment of nanoparticles due to the different neighborhood in the material. The free volume that characterizes the density of material is modified and, consequently, the penetration of fluids (solvents, oxygen) is rather favorable to degradation. The diffusion of xylene in ethylene-propylene diene terpolymer is unlike, if material presents different consistency (Fig. 14, [191]). The competitive radiochemical processes, crosslinking of polymer and degradation of covering layer are the most important reasons responsible for the different shapes of swelling curves. 

The effectiveness of an MPBD type additive when pre-coated onto precipitated calcium carbonate is demonstrated in Table 4.5. This compares uncoated, fatty acid coated, and MPBD coated fillers in a crosslinked ethylene-propylene-diene terpolymer (EPDM) elastomer and clearly shows the benefits arising from the use of the latter coating. 

On the basis of experimentally measured deviations of the equilibrium degree of swelling in -heptane from the additive value calculated for cross-linked heterophase blends composed of butadiene-acrylonitrile mbbers of different polarities and ethylene-propylene-diene terpol5miers of the known comonomer composition and stereoregularity of propylene units, the density of interfacial layer and the amount of chemical crosslinks in it have been characterized. The effects of isomers of butadiene units, the ratio of comonomers in ethylene-propylene-diene terpolymers, and the degree of isotacticity of propylene units on the intensity of interfacial interaction in covulcanizates have been analyzed. 

Formation of a strong interfacial layer is the key factor of the mechanism describing retardation of ozone degradation of a diene rubber by elastomer additives with a low degree of unsaturation [1-4]. The effect of comonomer ratio in ethylene-propylene-diene terpolymers (EPDMs) and stereoregularity of propylene units on the interfacial interaction and the amount of crosslinks in ihe interfacial layer was considered for heterophase crosslinked blends with butadiene-acrylonitrile mbbers (BNRs) of different polarities. 

Copolymerization of ethylene and propylene produces an elastomeric polymer that is virtually inert because of the absence of carbon-carbon double bonds (EPM). Such polymers thus tend to be crossUnked with peroxides or by radiation. To improve the reactivity of ethylene-propylene copolymers, 1-10% of a third monomer can be added to give a terpolymer or ethylene-propylene-diene monomer (EPDM). The primary diene monomers used in EPDM are 1,4-hexadiene, dicyclopentadiene, and ethyUdene norbomene. Introduction of an unsaturated monomer such as ethylidene norbomene will enable use of sulfur-based crosslinking systems. 

A very important thermoplastic elastomer is comprised of a blend of polypropylene (PP) with an ethylene-propylene-diene (EPDM) terpolymer. This latter material is, of course, a crosslinkable thermoset rubber ... 

The EP thermoplastic elastomers are distinguished from the crossUnked analogues, which are not thermoplastics since reforming is impossible. A very important thermoplastic elastomer is comprised of a blend of an EP copolymer with an ethylene-propylene-diene (EPDM) terpolymer. This latter material is, of course, a crosslinkable thermoset however, these materials can be processed as thermoplastics if the crosslinkable component is present at low enough concentration to be present as an isolated phase. Melt-processing causes the formation of chemical bonds within the isolated rubber phase, a process called dynamic vulcanization. A commercial example of this type of material is Santoprene [4] manufactured by Advanced Elastomer Systems. Other blends of noncrosslinkable TPEs with crosslinkable materials are used commercially. These materials are classified as elastomer blends and are the subject of Chapter 12. 

Polyurethane elastomers (some TUP, thermoplastic polyurethane) These terpolymers can be used uncured for most applications however, selected grades can be eross-linked to enhance properties. As a family these elastomers are tough and wear resistant. They have excellent chemical resistance and flexibility. They can have excellent clearity. Applieations include cable jackets. Automotive fascia, connectors, fittings, and many, many more. Ethylene-Propylene-Dlene Terpolymers (EPDM) These terpolymers typically contain a few percent of a diene such as hexadiene. This material is easy to fabricate and then is usually heat-treated at 125"C to 175 C to induce crbss-linking. The physical properties are much different after crosslinking. Commonly, they are heavily formulated for applications which include wire jacketing systems, automotive hoses, and roof sheeting. 

The isoprene units in the copolymer impart the ability to crosslink the product. Polystyrene is far too rigid to be used as an elastomer but styrene copolymers with 1,3-butadiene (SBR rubber) are quite flexible and rubbery. Polyethylene is a crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and diene (e.g., dicyclopentadiene, hexa-1,4-diene, 2-ethylidenenorborn-5-ene) are elastomers (EPR and EPDM rubbers). Nitrile or NBR rubber is a copolymer of acrylonitrile and 1,3-butadiene. Vinylidene fluoride-chlorotrifluoroethylene and olefin-acrylic ester copolymers and 1,3-butadiene-styrene-vinyl pyridine terpolymer are examples of specialty elastomers. 

Terpolymerization, the simultaneous polymerization of three monomers, has become increasingly important from the commercial viewpoint. The improvements that are obtained by copolymerizing styrene with acrylonitrile or butadiene have been mentioned previously. The radical terpolymerization of styrene with acrylonitrile and butadiene increases even further the degree of variation in properties that can be built into the final product. Many other commercial uses of terpolymerization exist. In most of these the terpolymer has two of the monomers present in major amounts to obtain the gross properties desired, with the third monomer in a minor amount for modification of a special property. Thus the ethylene-propylene elastomers are terpolymerized with minor amounts of a diene in order to allow the product to be subsquently crosslinked. 

Definition Elastomer based on stereospecific linear terpolymers of ethylene, propylene, and diene vulcanized by sulfur or peroxide crosslinking ... 

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