نشریه صنعت لاستیک ایران
پیاپی 101 (بهار 1400)

Calenders and two-roll mills as a tool for forming materials )mostly polymers( have a special role in the production lines of various industries, including rubber industry. Despite the apparent simplicity and not-so-difficult application, as will be shown in this study, the hydrodynamics behavior of the flow material through them is complex and subject to various factors. In the present study, first these type of equipments and important points of their design and operating conditions are introduced. In the following, the hydrodynamic modeling of the flow between the rolls is discussed and the Gaskell’s model is introduced as a basic model that is the basis of most other developed models. Finally, other types of models that have been developed to determine the hydrodynamic behavior of rolls along with their characteristics are introduced. These models predict the flow rate based on geometric parameters and material properties. They also determine velocity, pressure and stress profiles, and in some cases temperature in the flow between the rolls. The use of results of these models depends on the desired design and operational needs.

Lignin is a reinforcing filler with properties such as abundantannually renewable, low weight, high biological efficiency, and wide ecological adaptability. These properties are causedincreasing attention from researchers and become an alternative to carbon black in the rubber industry. in this paper, we try to briefly review the lignin. In this regard,initially, the chemical structure of lignin and its structuresareconsidered. it is obvious from the application and process point that this polymer has little tendency to spread in the rubber matrix due to polar functional group and so it will not appear as agglomeration in rubber compoundand thereforewon’t be as reinforcing filler. There have been studies in order to solve this problem and improved the reinforcing properties of lignin. These include modifying the mixing process, increasing the interfacial bonding strength between lignin and the rubber, formation of nano structure with lignin and use of hybrid technologies with other filler.Here some of these methods and the effects of lignin on its curing, mechanical and thermal properties are summarized.

The main goal of this research is the preparation and study of nanocomposites based on carboxylated nitrile butadiene rubber )XNBR( and epoxy resin reinforced by halloysite nanotubes )HNTs(. The effect of various HNTs loadings on the cure characteristics, morphology, cure kinetics and mechanical properties of binary XNBR/Epoxy systems was investigated. The results of cure rheometer indicated that the introduction of HNTs into the XNBR/Epoxy matrix leads to a decreased scorch time up 25% and higher maximum torque values. The resulted SEM photomicrographs of fractured section from tension tests revealed a more rough fractured surface of nanocomposites containing HNTs with a distributed of nanotubes into the polymer matrix. The study of cure kinetics show that the introduction of HNTs into the polymer system decreases the activation energy needed for curing reaction up to 40% . The results of tension tests demonstrated a higher Young’s modulus up to 1.46 MPa and tensile strength up to 2.58 MPa with higher loadings of HNTs into the XNBR/ Epoxy matrix. The analyses of XNBR/Epoxy/HNTs nanocomposites indicated that with the natural and inexpensive reinforce nano materials, it is possible to make nanocomposites with higher mechanical strength up to 40% with respect to neat polymer.

Elastomeric nanoparticles )ENPs( have been widely used in thermosetting resins and thermoplastics, and when used to modify the surface of polymers, its effect at the nanoscale has been considered. The size of elastomeric nanoparticles is well controlled by the latex particle size, and using this process, a particle size of less than 100 nano meters is produced and has a narrow distribution.Elastomeric nanoparticles simultaneously increase the toughness and heat resistance of plastics. The addition of elastomeric nanoparticles to rubbers and thermoplastics improved the surface, and improved the dispersion of elastomeric nanoparticles in the polymer matrix. In this paper, a review of sample preparation, and the effect of elastomeric nanoparticles and their application, and the study of the effect of elastomeric nanoparticles on the physical, mechanical and thermal properties of thermosetting.

Rubber is the main element of tires and the main part of the tire consists of rubber. Tire and track heating is caused by hysteresis effects due to the deformation of the rubber during operation. Temperature in tire components depends on many factors, including tire geometry, inflation pressure, vehicle load and speed, road type and temperature and environmental conditions. In this study, using the theory of heat production in tire and relying on the finite element and calculating the stress and strain field of different parts of the tire, the temperature field of a steady-state rolling truck radial tire is predicted. ABAQUS software is used in this finite element prediction. It is shown that the results predicted using ABAQUS software are in significantly better agreement with the experimental results.

Predicting corporate financial distress is one of the main issues facing managers, which can significantly contribute to companies' success and survival because corporate managers can be informed of financial distress and bankruptcy by providing warning and timely signals. Therefore, it is possible to avoid wasting resources and damages due to bankruptcy through proper management. This study's main purpose was to select the financial variables affecting the prediction of financial distress of companies listed on the Tehran Stock Exchange and then to predict financial distress using the ANN method. Therefore, first, 106 companies were selected by the simple random sampling method. Their financial data were extracted during 2007-2020. The relationship between variables was examined through the Pearson correlation test. Out of 34 financial ratios, 24 ratios with a significant relationship were selected. Finally, the ANN method was used to predict corporate financial distress, in which the financial distressfulness or non-distressfulness of 103 companies was correctly predicted. Comparing the prediction made by the ANN method with the actual values of the dependent variable in 2020, it was found that this method correctly predicted the corporate financial distress with a confidence level of 97%.

The purpose of present research was to consider analysing the impact of Total Quality Management and Entrepreneurial Orientation on Performance of SMEs. This Practical research was done by using descriptive- correlation method. The statistical population of the study consisted of 460 managers of SMEs in Jay Isfahan industrial town. 210 managers determined randomly as the sample size by Krejcie and Morgan Table. To collect data, three questionnaires of Total Quality Management of Jayaram(2010), Entrepreneurial Orientation of Hughes and Morgan(2007),and Firm Performance of Sahoo and Yadav(2017) were used. The validity of the questionnaires was confirmed by the content validity and validity of the structure and its reliability was achieved by cronbach'salpha method of 0/819,0/822,and0/88 6,respectively. The data was analyzed by structural equation modeling in MPLUS advanced software. The research findings showed that total quality management and Entrepreneurial Orientation have a positive and meaningful effect on Firm Performance. According to the results, Total Quality Management and Entrepreneurial Orientation has a great influence to improve the performance in SMEs.

The purpose of this paper is to present the framework of a fourth paradigm since the existing three paradigms in quality management are not sufficient any more to understand what happened in the past and surely fail to understand what is happening at the moment and needed in future. A literature review has been undertaken on different visions on quality management that are used. The underlying principles have led to three quality paradigms. Literature on quadrant models is studied to place the three existing paradigms and identify the possible characteristics of the fourth. One can discern four quality paradigms in quality management: the Empirical Paradigm, the Reference Paradigm, the Reflective Paradigm and the Emergence Paradigm. The use of these paradigms differs according to the context. Together they form a concept of Total Quality Management. At the moment the Emergence Paradigm has not had enough attention although it might be the best equipped to find new ways of working for the organisations in the current context. In the literature review the authors selected seven journals in the Business Source Premier database: Total Quality Management (Total Quality Management & Business Excellence); the Academy of Management Review; Product and Operations Management; Organisational Dynamics; the Harvard Business Review; the Sloan Management Review and Organisational Behavior and Performance. In the advanced search mode the authors entered two subjects: “quality management” and “paradigm”. The selected results (in total 289 articles) were examined for its fitness for answering the questions above. That resulted in a selection of 26 articles that are being used in the literature review. The Emergence Paradigm can be further investigated on its use for quality management in organisations in times of emergent change. Some first insights have been presented here. The EmergenceParadigm can have impact beyond the field of quality management. The paper provides new insights in the essence of quality management in times of change and clarity on the usability of the thoughts and tools of four different paradigms in the twenty-first century.