Preparation Of Epdm Foams And Study On Its Structure And Properties

Rubber foams are a conventional material, which have been widely used in the field of agriculture and industry etc. However, the study of the rubber foams is still in its infancy with a few correlative published papers, in which the studies on the rubber foams mainly involved preparation methods and mechanical properties of testing, especially focus on the delicate balance of two simultaneously occurring reaction---the curing of the rubber and the decomposition of the blowing agent. The relationships among the preparation, morphology and mechanical properties of the rubber foams are still unclear.In general, the conventional formulation contains non-reinforcing filler and lower-surface-area carbon black, which would lead to lower mechanical properties of resultant EPDM foams, so that the EPDM foams cannot satisfy the requirement of high mechanical properties. In this paper the EPDM foam was prepared in a circular hot air, which contains higher-surface-area carbon black N330, used as reinforce filler. The effects of accelerator, temperature, filler content and blowing agent content etc. on the structure of EPDM foam were investigated. On the basis of the analysis on the match between curing and blowing, a new processing route of EPDM precured technology was put. The effects of precured compound on the rheological properties and gel content were investigated, the autocatalytic model was used to analyze the reaction kinetics of curing and blowing, the compressive stress-strain and relaxation behaviors were studied. The main contents and conclusions are listed as follows.The effect of accelerator on the macroscopical appearance was investigated. The results show that when TMTD/CZ (1/1) or M/TMTD/TRA (1/0.5/0.5) used as accelerator, the cure rate of EPDM is very rapid so that the resultant foam articles broken and becomes a useless product. However, when D used as accelerator, the initiating time of vulcanization is earlier than that of blowing and the end time of vulcanization is later than that of blowing, which leads to a successful blowing process and indicates that vulcanization and blowing are well matched each other. SEM shows that the foams have a closed-cell structure and the larger cells inlaying among the smaller cells. With AC content increasing, the density of foam article decrease and the cell size increase. With N330 content increasing, the viscosity and modulus of uncured EPDM compound increase obviously, the density of foam article increase and the cell size decrease. The sunpar 2280 could make the modulus and viscosity of uncured EPDM compound decrease, but it cannot obviously decrease the density of foam article, which indicate that the match between curing and blowing is not sufficient condition for the blowing process.In order to resolve the difficulty about the lower efficiency of blowing agent, a new processing route of EPDM precured technology was put, that is, EPDM foam was prepared by dynamically vulcanizing EPDM compound in a HAAKE rheometer firstly, then mixing the partially precured EPDM compound with a blowing agent and a sulphur vulcanizing system on a two roll mill, finally, the compound was foamed in a circulating hot air oven. The effects of pre-crosslink degree of EPDM compound on the rheological properties and gel content were investigated. The results show that pre-crosslink degree of EPDM compound could be effectively controlled by adding sulphur content in dynamic vulcanizing process. With sulphur content increasing, the gel content, the dynamic storage modulus (G′), the loss modulus (G″) and the complex viscosity (η*) of precured EPDM compound increase. With increasing the frequency, the dynamic storage modulus (G′) and the loss modulus (G″) increase, while the complex viscosity (η*) decreases, which indicates the pseudoplastic behavior of the compounds. The cure rate of partially precured EPDM compound is not affected by the precure in the HAAKE. With increasing the crosslink density of precured EPDM compound, the foam density of EPDM compound begins to decrease then to increase. For optimum partially precured EPDM compound, the density of EPDM foam decrease with AC content increase, when AC content is 12 phr, the density of foam could decrease to 0.09 g/cm3. The dynamic vulcanization technology could be used for other blowing formulation, which is difficulty to complete the successful foam in conventional methods.The vulcanization and blowing characteristics of the rubber compounds were measured on a moving die rheometer. The results show that kinetic parameters determined from the autocatalytic model equation have good agreement with the experimental results, and the sum of the values of n and m related to reaction order changes with temperature. The calculated activation energy of AC decomposition is higher than that of rubber cure, which indicates the rate of blowing agent AC decomposition accelerates more quickly than that of rubber vulcanization with increasing temperature. In the course of bubble growth, there exists cell-to-cell diffusion for small cell having higher gas pressure, which leads to the structure that the larger cells inlay among the smaller cells.The compressive and relaxation behaviors were measured on an Instron 4465 electromechanical tester. The results show that the compressive stress-strain curve of foams with lower relative density includes three regimes: first is a linear elasticity at small deformations, followed by a wide collapse plateau, which leads to densification where stress rises steeply, while for the foams with higher relative density, the compressive stress-strain curve shows two regimes: the comparatively longer linear elastic region, then leads to densification. The energy absorption capabilities are closely relationship with the relative density of foam article and the permitted stress. The efficiency of energy absorption (E), the ideality parameter (I) and energy-absorption diagram approach could offer methods to evaluate and compare the performance and suitability of the energy absorption of different foam, which optimizing the choice of foam for appropriate utilization.The innovation points of this paper are listed as follows.(1) The dynamic cure processing has been first applied to rubber blowing procedure, which is a new thought to prepare the rubber foams. That is, EPDM foam was prepared by dynamically vulcanizing EPDM compound in a HAAKE rheometer firstly, then mixing the partially precured EPDM compound with a blowing agent and a sulphur vulcanizing system on a two roll mill, finally, the compound was foamed in a circulating hot air oven, and the foam articles have good appearance and adjustable cell structure. The craft emphasizes the pre-crosslinking degree of EPDM compound, not the strict match between the curing rate of rubber and decomposing rate of blowing agent, which use the commonly used raw materials, the simple formula and easy to control the technological conditions. Thus, the craft has many advantages, such as the production cycle short, easy to operate and decreasing blowing agent content etc.(2) The key factor that impacts the mechanical properties of foam articles is the composition of EPDM compound. The filler with lower surface area carbon black could give a lower reinforcing effect, which lead to lower mechanical properties of resultant EPDM foam. Thus, it is very important to adopt the higher-surface-area carbon black N330 as reinforcing filler to achieve the higher mechanical properties of EPDM foam. The effect of accelerator, temperature, filler content and blowing agent content etc. on the structure of EPDM foam were investigated systematically, and the foam articles with smooth surface are prepared.(3) The compressive stress-strain and relaxation behavior are studied. Especially based on the stress relaxation characteristics of foam articles, the stress relaxation model is proposed, which could explain the relaxation behavior of foam article very well.