The thermochemical recycling of natural rubber (NR) and ethylene-propylene-diene rubber (EPDM) vulcanizates with disulfides was studied. NR sulfur vulcanizates were completely plasticized when heated with diphenyldisulfide at 200 °C. It could be concluded that both main chain scission and crosslink scission caused the network breakdown. NR peroxide vulcanizates were less reactive towards disulfide at 200 °C, and only reacted through main chain scission. For EPDM a temperature range of 200–275 °C was studied. In the presence of diphenyldisulfide at 200 °C there was almost no devulcanization of EPDM sulfur vulcanizates, and at 225 and 250 °C there was only slightly more devulcanization. A decrease in crosslink density of 90% was found when 2×10−4 mol diphenyldisulfide/cm3 vulcanizate was added and the EPDM sulfur vulcanizates were heated to 275 °C. EPDM peroxide vulcanizates showed a decrease in crosslink density of ca. 40% under the same conditions. The lower reactivity of EPDM towards disulfide compared with NR is the result of higher crosslink densities, the presence of a higher percentage of more stable monosulfidic crosslinks and the fact that EPDM is less apt to main chain scission relative to NR.

In a previous study, the mechanism of EPM peroxide vulcanization in the presence of various aromatic bis(allyl)esters was elucidated. It was concluded that the elastomer-coagent blend was phase separated and that during vulcanization chemical crosslinks are formed between the elastomer matrix and coagent domains. In this study the effect of the chemical structure of the coagent on the ultimate properties of the vulcanizate is reported. For this purpose a series of new coagents has been synthesized. It was found that bis(allyl) coagents with relatively flexible interlinking segments provide vulcanizates with improved mechanical properties.

Pellethane@ 2363 60Afilms and tubings were chemically modified and the effect of these modifications on platelet deposition was studied. Grafting of high molecular weight poly(ethylene oxide) and graft polymerization of methoxy poly(ethylene glycol) 400 methacrylate resulted in surfaces with a good water wettability. The increased hydrophilicity of these modified surfaces could be demonstrated by contact angle measurements. The platelet deposition was investigated with tubings in a capillary flow system, using different types of perfusates. Platelet deposition from a buffer-containing perfusate on surfaces modified with either high molecular weight poly(ethylene oxide) or methoxy poly(ethylene glycol) 400 methacrylate was almost absent and less than on Pellethane 2363 60A. Using a titrated plasmacontaining perfusate the amount of deposited platelets on Pellethane 2363 60A modified with high molecular weight poly(ethylene oxide) was low and about the same as on unmodified surfaces. However, a marked reduced platelet deposition compared to unmodified Pellethane 2363 60A was found when the platelets were activated by Ca2+ ionophore. The improved blood compatibility of the modified Pellethane 2363 60A tubings obviously indicates the favourable effect of the presence of grafted PEG on the surface. Keywords: Copolyether urethanes. poly(ethylene oxide), grafting, Platelet depositionPoly(ethylene oxide) (PEO) is more and more regarded as a polymer with interesting blood contacting properties. The low affinity of PEO for proteins and other blood components has stimulated many investigators to study the interactions of blood and biomaterials based on PEOle7.In an attempt to improve the blood compatibility of a commercial copolyether urethane, Pellethane@ 2363 80A (Pell80A). several techniques for grafting PEO onto Pell80A were investigated. Grafting of high molecular weight PEO with dicumyl peroxide (DCP) and graft polymerization of methoxy poly(ethylene glycol) 400 methacrylate (M PEGMA-400) were examined. The first method is based on crosslinking of high molecular weight polyethers. Cross-linked blends of poly(propylene oxide) and PEO have shown a good blood compatibility4. Surface analysis of these blends suggested that the good blood contacting properties of these materials may be ascribed to preferential presence of PEO at the polymer-water interface'. In the present work, Pell 80A substrates were dipped in a solution of PEO and DCP. After drying, the PEO/DCP coated substrates were UV or heat treated in order to form a network of PEO and Pell

The synthesis, iron (III)-chelating properties, and antibacterial activity of several compounds containing the 3-hydroxy-2-methyl-4(1H)-pyridinone (HMP) moiety are described. Using the HMP derivatives iron (III) could be mobilized from iron (III)-binding proteins at physiological pH with a rate order of transferrin > lactoferrin > ferritin. Addition of HMP-containing compounds to a growth medium at a concentration of 20 mM/L resulted in a complete inhibition of the growth of Escherichia coli and about 90% inhibition for Listeria inocua after 7 h of incubation at 37 degrees C. After inhibition of bacteria growth by the HMP derivatives growth started again when ferric ions were added to the medium, which implies that the antibacterial activity is due to a limitation of iron available to the organisms.

Ethylene-propylene-diene rubbers (EPDM) with 2-ethylidene-5-norbornene (ENB), dicyclopentadiene (DCPD), and 1,4-hexadiene (HD) as third monomers have been vulcanized with peroxide and with a conventional sulfur vulcanization recipe, and their devulcanization was subsequently investigated for recycling purposes. The behavior of these vulcanizates during pure thermal devulcanization depends on the EPDM third monomer and the crosslinker used. Peroxide vulcanizates of ENB-EPDM devulcanize only to a small extent and predominantly by random scission, whereas peroxide vulcanizates of HD-EPDM devulcanize by crosslink scission. In contrast, sulfur vulcanizates of ENB-EPDM, devulcanize mainly by crosslink scission. During devulcanization of sulfur-cured HD-EPDM, scission of both crosslinks and main chains occurs. Sulfur-cured DCPD-EPDM cannot be devulcanized but shows further crosslinking instead. In those cases, where purely thermal devulcanization is already effective to a certain extent, diphenyldisulfide as devulcanization agent increases the effectivity during thermochemical devulcanization. Hexadecylamine as an alternative devulcanization agent is effective for ENB-EPDM but does not contribute to thermochemical devulcanization of HD-EPDM. In summary, devulcanization proceeds by different mechanisms in ENB-EPDM, DCPD-EPDM, and HD-EPDM. Explanations are given in terms of the chemical structures of the third monomers, the corresponding crosslinks, and devulcanization agents.