Einfluss der Modifikation von Polymerketten durch Vernetzer und Beschleuniger auf die Elastomereigenschaften – Teil 1

Considerable attention is paid to the influence of crosslink density and crosslink structures on behavior of polymer chains and properties of elastomers. However, a very important parameter seems to be underestimated: the modifications to the polymer chains by curatives, formed by sulfur and fragments of accelerators. The present paper intends to draw attention to this important contribution to performance of spatial networks. Emulsion styrene-butadiene rubber (E-SBR) samples, cured with tetramethylthiuram disulfide and sulfur (TMTD/S8), and zinc dialkyl dithiophosphate with sulfur (ZDT/S8), were studied. They were characterized in detail in terms of crosslink density and crosslink structures. Microscale techniques were used to obtain information about the behavior of the polymer chains: PALS to study the free volume structure; DSC and DMA to monitor the glass transition process. Properties such as static mechanical performance and thermal stability were also evaluated. All of the investigated characteristics were influenced by a combination of crosslink density, crosslink structures, and, to a large extent, by the modifications of the polymer chains. The effect of the modifications is dependent on the amount and the structure of the curatives’ molecules. On the basis of the obtained results, the reliability of „phr” unit used for calculation of the curatives’ amount has been queried. Furthermore, it has been demonstrated that DSC, DMA and PALS techniques can provide evidence for the presence of the modifications on the polymer chain by curatives. Part 1 describes how the composition of the vulcanization system generally influences the crosslinking structures. It contains the experimental part and the comparison of the degree of crosslinking and crosslinking structures after vulcanization with TMTD/S8 or ZDT/S8

Effect of polymer chain modifications on elastomer properties

Considerable attention is paid to the influence of crosslink density and crosslink structures on the behavior of polymer chains and properties of elastomers. However, a very important parameter seems to be underestimated: the modifications to the polymer chains by curatives, formed by sulfur and fragments of accelerators. We draw attention to this important contribution to performance of spatial networks. The emulsion styrene–butadiene rubber samples, cured with tetramethylthiuram disulfide and sulfur (TMTD/S8) and zinc dialkyl dithiophosphate with sulfur (ZDT/S8), were studied. They were characterized in detail in terms of crosslink density and crosslink structures. Microscale techniques were used to obtain information about the behavior of the polymer chains: positron annihilation lifetime spectroscopy (PALS) to study the free volume structure and differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) to monitor the glass transition process. Properties such as static mechanical performance and thermo-oxidative stability were also evaluated. All of the investigated characteristics were influenced by a combination of crosslink density, crosslink structures, and, to a large extent, by the modifications of the polymer chains. The effect of the modifications is dependent on the amount and the structure of the curatives’ molecules. On the basis of the obtained results, the usefulness of the ‘‘phr’’ unit used for calculation of the curatives’ amount has been queried. Furthermore, it has been demonstrated that DSC, DMA, and PALS techniques can provide evidence for the presence of the modifications on the polymer chain by curatives

Effect of electron beam irradiation on structure and properties of styrene-butadiene rubber

Crosslinking and chain scission occur simultaneously during irradiation of polymers and influence their properties in an opposite way. To characterize the radiation-induced changes and evaluate how they influence the performance of the polymer, quantification of these reactions is crucial. In this work, the effect of styrene-butadiene rubber (SBR) radiation curing with doses ranging from 25 kGy to 200 kGy, at room temperature and air atmosphere was investigated. The Charlesby-Pinner and Charlesby-Rosiak equations were used to characterize the curing process. Only the Charlesby-Rosiak equation gave good linear representation of the data and allowed to obtain the parameters, which characterize the irradiated SBR system: (i) gel dose, (ii) ratio between chain scission and crosslinking, and (iii) radiation yields of crosslinking and chain scission. These parameters showed that SBR is quite resistant to ionizing radiation, where crosslinking predominates over chain scission. The effect of irradiation on in-rubber properties is discussed. An increase in radiation dose resulted in change of tensile strength, elongation at break, mechanical modules, hardness, glass transition temperature and thermo-oxidative stability. Freezing point depression experiments were also conducted. The depression of the solvent freezing temperature in swollen polymer gels provided information on polymer network and mesh size, staying in agreement with the crosslink density values