Chlorobutyl Covulcanization Chemistry and Interfacial Elastomer Bonding

Abstract

A new analytical and diagnostic technique has been developed and applied to covulcanized Chlorobutyl—polydiene rubber blends that indicates the existence or absence of interfacial bonds. This technique of differential solvent swelling is based upon solvent—elastomer interaction parameters and draws upon the analogy to filler-adhesion analysis of vulcanized networks. Interfacial bonds between dispersed Chlorobutyl and polydiene rubber phases are first obtained with very active thiuram and thiuram tetrasulfide curative systems. Subsequently less active curatives utilizing bis-alkylphenol polysulfides as sulfur donors were also found to promote interfacial bonds. By means of mercaptan probes it was established that strong evidence of interfacial bonds in covulcanized networks was associated with a preponderance of monosulfidic crosslinks. Prolonged heating, which matures polysulfidic links to more thermally stable monosulfidic links, did not produce strong interfacial bonds where none existed after the initial vulcanization cycle. Thus, interfacial bonds must be formed with more thermally stable monosulfide links during the initial stages of vulcanization. Reinforcing carbon black has a minimal effect upon the acquisition of interfacial bonds or the sulfur-bond chemistry. The curative formulation remains the factor which governs production of the monosulfidic links required for strong interfacial bonding. A definite correlation was found between interfacial bonding and physical strength of fully compounded Chlorobutyl—SBR covulcanized blends. Carbon-black reinforced systems covulcanized with a sulfur donor, such as bis-alkylphenol polysulfide, as the sole source of sulfur, displayed tensile strengths and rupture energies considerably greater than the equivalent systems containing elemental sulfur.

Compatibilization efficiency of carboxylated nitrile rubber and epoxy pre-polymer in nitrile/acrylic rubber blends.

“…Since the ∆M values are lower, one can attribute this behavior as a covulcanization phenomenon, in which both rubber components take part in the network. According to some reports in the literature, the lightly swollen rubber phase restricts swelling of the highly swollen phase because of the interfacial crosslinking [24][25][26][27] . This phenomenon is possible because the BMI used as the co-agent for the peroxide curing system may also react with the hexamethylenediamine formed through the decomposition of the Chemac Park 50 (HMDAC), which is used for curing the ACM phase [21] .…”

Polyblends of Polyurethane and EVA Elastomers (Peroxide cure)

“…Differential solvents swelling [8] in DMF and toluene were carried out followed by a Kraus plot [9] to study the phase adhesion. Infrared spectra of the thin film of pure PU, EVA and a (50:50) blend of PU/ EVA (without curatives) were taken using a Perkin-Elmer model 837.…”

Modification of EPDM with Alkylphenol Polysulfide for Use in Tire Sidewalls, 1 – Mechanical Properties

“…They are particularly recommended for butyl-and halobutyl rubber-based applications. [16][17][18][19] There are several benefits by using alkylphenol sulfides as curing agents: they are nitrosamine-free, have no blooming problems, provide better heat resistance, improve dynamic fatigue properties, enhance adhesion, and may act as tackifier. Moreover, due to the phenol group in their structure, they are believed to have a good affinity with carbon black, which may improve the carbon black distribution after EPDM modification and consequently the mechanical properties.…”