نشریه صنعت لاستیک ایران
پیاپی 104 (زمستان 1400)

Sulfur vulcanization is the most common method for creating crosslinks in rubber compounds and creating a three-dimensional network. The most stable form of sulfur in the environment is rhombic (Sα), which is an octahedral ring and known as soluble sulfur. Soluble sulfur was previously used for vulcanization. This substance can migrate to the surface of rubber and this causes problems. It has been replaced by polymeric sulfur to solve problems. In this study, the effect of amount of soluble sulfur and polymeric sulfur on rheometric diagrams at two temperatures was investigated and compared with each other. The results showed that increasing the amount of sulfur decreases the scorch time and increases the difference between the minimum and maximum torque. In addition, polymeric sulfur has a higher efficiency, and the properties of its rheometric diagram are similar to those with higher sulfur content. In addition, the effects of temperature on rheometric diagrams in both sulfurs are similar. These diagrams are simulated with the help of mathematical equation and the related parameter in each case is calculated with the curve fitting.

Tires are an important and special part of car that have a directly relation with the functions such as braking, acceleration and passenger comfort. Increasing the durability of the tire will increase road safety. It is important to note that the fatigue life must be longer than wear life. If the wear life is prolonged, the fatigue life expectancy has to be expanded correspondingly. Fatigue is a common cause of failure of a steel belted radial tire in use. Thermal, speed, tire structure and aging have an important effect on tire fatigue life. In this paper the effect of factors such as thermal, speed, fatigue life and aging on durability and relation between them are studied. Crack initiation and crack growth at filament ends and rubber are also studied in details. At the end, it is shown that the cord type and EPDM have a significant influence on belt endurance. In this paper, it is shown that the mechanical factor, especially the tire fatigue, causes crack initiation and crack growth due to cycling load. Also, heat is generated in the critical areas of the tire due to the visco-elastic property of the compound, which reduces the life of the tire. Also aging along with thermal reduces the tensile strength and degrades the tire.

Extruder as a material forming tool, is a basic and important equipment in the production process in various polymer industries, including rubber industry, industries based on plastic forming, food industry, etc. Since in most industries, extruders act as intermediate equipment and in series with other equipment, the production capacity of the product can depend on the amount of production in the extruder, which is a kind of flow rate of the extruder. Various factors affect the flow pattern and consequently the discharge output of the extruder. Knowing these factors and how they affect them is very effective in predicting the performance and determining the optimal operating points of this type of equipment. Therefore, in the present study and in two parts, two of the most important methods of modeling the fluid flow inside the extruders are investigated and the strengths and weaknesses of each in predicting the flow profile as well as The output flow of the extruder is determined. In the first part, Custer model is examined and in the second part, Tadmor and Gags model will be examined. The important point that has not been explored so far is that despite the various simplifications, the results of these models can be used to give an acceptable prediction of the performance of various extruders in industry.

Epoxy resin is used as a wind turbine, coating, adhesive and base material for composites and is widely used in automotive, electronics, and construction industries. Modification of the surface of epoxy nanocomposites in the presence of silica nanoparticles, due to increased adhesion and covalent bonding, increases the impact strength and Also, by adding silica nanoparticles to epoxy resin, the Young's modulus increases linearly, which is due to the increase in nanoparticle dispersion and reduced stress concentration. By adding silica nanoparticles to epoxy resin, the maximum heat flow temperature decreases and the curing rate increases, and also causes the heat flow curve of epoxy nanocomposite to be wider. The presence of silica nanoparticles reduces the activation energy and silica nanoparticles act as a catalyst in the curing reaction with epoxy resin. Two important factors in reducing the thermal degradation of epoxy nanocomposites are proper dispersion of nanoparticles and non-agglomeration. Silica nanoparticles increase the maximum temperature of thermal degradation, thermal stability and the percentage of residual char. In this research, the modeling of curing kinetics of epoxy nanocomposites on morphology, rheological and mechanical properties, activation energy, curing degree, heat flow and investigation of thermal stability and thermal degradation has been reported.

In today's world, the most important factor in development is promotion of the human resources productivity. Identifying the effective parameters on the human resources productivity and prioritizing them in promotion of the human resources productivity has been significant and can be promising for achieving organizational and national productivity. In this research, an attempt is made to identify the effective parameters on the promotion of human resource productivity (case study Iran Tire Company). The statistical population of the study was 120 employees and the sample size was 92 people. The method of the present research is descriptive-survey. The data collection tool is a researcher-made questionnaire with 28 questions.The validity of the questionnaires was confirmed by a group of university professors and also, the reliability of the questionnaires was 91% using Cronbach's alpha coefficient which indicates the accuracy and high capability of the questionnaire. SPSS software and Kolmogorov-Smirnov tests and parametric t-test were used to analyze the data and information. The results show the confirmation of 2 hypotheses and the non-confirmation of 5 hypotheses as the factors of clarity of job and environmental adaptation are effective on promotion of the human resources productivity in Iran Tire Company and the factors of ability, organizational support (Help), incentive, evaluation of performance and validity of decision are not effective on promotion of the human resources productivity in this company.

This study intends to investigate the impact of market risk management and commercialization risk on the performance of new service development. The research method used is descriptive survey. The statistical population includes 1080 managers and employees of Irene Insurance Company. The sample size was 284 based on Cochran's formula, which was selected by simple random sampling method. A questionnaire was used to measure the concepts and the collected data were analyzed using statistical, descriptive and inferential tests. The validity of the questionnaires was evaluated based on the validity of the structure and convergence and its reliability with Cronbach's alpha coefficient. The research model was tested based on the partial least squares method and SmartPLS software. The results of this study indicate that market risk management has a positive effect on the performance of new service development. Commercialization risk also has a positive effect on the performance of new service development.

Entrepreneurial awareness of managers and employees and having entrepreneurial skills are considered as an important mechanism of entrepreneurship development. Today, the expectations of most people from organizations have stepped into social demands; This moves organizations to meet social expectations. This research is practical in terms of purpose and quantitative in terms of data collection method. The statistical population is 50 managers and experts of Artavil Rubber Company, of which 44 people were selected as a simple random sample. PLS and SPSS software were used for analysis. Therefore, in order to evaluate the reliability of the research measurement model, factor load coefficients, Cronbach's alpha coefficients and combined reliability, convergent validity and divergent validity were used. The results show that the linear relationships between the variables have been confirmed and entrepreneurial awareness can affect the development of entrepreneurship and an organization can succeed if it has employees and managers with entrepreneurial skills and entrepreneurial awareness that can ultimately be socially responsible. Create in the organization environment.

The plastic products industry comprises a wide range of products from basic products to intermediate and final products. The expansion and application of plastic products in various industries, as well as the satisfaction of the needs of households, has made this industry one of the main industries and its export diversification is important for the countries. Using new structuralists approach, product space theory and product network science, this paper uses six-digit HS codes for 128 countries over the period 2018-2014 to represent the increase in the diversity of Iranian exports in the plastics industry and determine their sequence of activation. The findings indicate that out of 122 plastic product codes, Iran has 14 products that have an revealed comparative advantage in exports, 47 products with a implied comparative advantage, and 61 products with no revealed and implied comparative advantage. In the next step, considering the positive opportunity gain index, products with implied comparative advantage were reduced from 47 to 12. Finally, using different strategies and applying a combined strategy of Borda and Copeland methods, the activation sequence of these 12 products were identified. According to the combined strategy, the export of rigid polyvinyl chloride pipes, ethylene polymer bags and flexible plastic pipes constitute the major part of Iran's export opportunities.