title: A new method to predict optimum cure time of rubber compound using dynamic mechanical analysis

authors: Shuib, Raa Khimi

subjects: rubber

abstract: The degree of vulcanization of a rubber compound has a big influence on the properties of the final product. Therefore, precisely defining the curing process including optimum cure time is important to ensure the production of final products having high performance. Typically, vulcanization is represented using vulcanization curves. The main types of equipment used for producing vulcanization curves are the oscillating disc rheometer (ODR) and the moving die rheometer (MDR). These can be used to plot graphs of torque versus time at a constant temperature to show how cure is proceeding. Based on the results obtained, optimum cure time (t₉₀) is calculated as the time required for the torque to reach 90% of the maximum achievable torque. In this study, the use of Dynamic Mechanical Analysis (DMA) for assessment of t₉₀ was assessed. DMA was carried out using shear mode isothermal tests to measure the changes in material properties caused by vulcanization. The results revealed that the shear storage modulus (G′), shear loss modulus (G′′), and tan δ all reflect the vulcanization process, however, tan δ gave the best representation of level of vulcanization. Indeed, the curve of tan δ was able to be used to derive the t₉₀ for rubber compounds and showed good agreement with the results from an MDR.

text: A new method to predict optimum cure time of rubber compound using dynamic mechanical analysis The degree of vulcanization of a rubber compound has a big influence on the properties of the final product. Therefore, precisely defining the curing process including optimum cure time is important to ensure the production of final products having high performance. Typically, vulcanization is represented using vulcanization curves. The main types of equipment used for producing vulcanization curves are the oscillating disc rheometer (ODR) and the moving die rheometer (MDR). These can be used to plot graphs of torque versus time at a constant temperature to show how cure is proceeding. Based on the results obtained, optimum cure time (t₉₀) is calculated as the time required for the torque to reach 90% of the maximum achievable torque. In this study, the use of Dynamic Mechanical Analysis (DMA) for assessment of t₉₀ was assessed. DMA was carried out using shear mode isothermal tests to measure the changes in material properties caused by vulcanization. The results revealed that the shear storage modulus (G′), shear loss modulus (G′′), and tan δ all reflect the vulcanization process, however, tan δ gave the best representation of level of vulcanization. Indeed, the curve of tan δ was able to be used to derive the t₉₀ for rubber compounds and showed good agreement with the results from an MDR.

year: 2013

title: A Comparative Analysis of Equine Mesenchymal Stromal Cells and Dermal Fibroblasts

authors: Leander, Alexandra Anneli Kristina

abstract: The aim of this study was to isolate and characterise equine mesenchymal stromal cells from various sources and to compare their biological properties to that of dermal fibroblasts. By using multiple conventional methods a comparative analysis of the different populations could be made. The results showed that little distinguishes mesenchymal stromal cells from dermal fibroblasts, they have the same morphology and growth characteristics, the same cell surface markers as demonstrated with immunocytochemistry and flow cytometry and the capacity to undergo trilineage differentiation into adipo-, chondro- and osteogenic lineages essentially becoming fat, cartilage and bone. An allogenic synovial fluid model was shown to induce a chondrogenic phenotype in equine mesenchymal stromal cells as well as dermal fibroblasts. A bio-activation assay was performed to evaluate cytokine production of cell populations after activation with Tumour necrosis factor alpha or inflammatory synovial fluid. All of the analysed cell populations demonstrated up-regulation of production of the anti-inflammatory cytokines IL-10 and TGF-β1, after activation with inflammatory synovial fluid, although significant values could not be obtained for every source. As for Prostaglandin E2, results were obtained for bone marrow stromal cells and dermal fibroblasts populations only. Their effects were in opposite; dermal fibroblast reduced the production of Prostaglandin E2 post activation. A functional bio-activation assay has shown promise as a method to distinguish equine mesenchymal stromal cells from dermal fibroblast populations.

text: A Comparative Analysis of Equine Mesenchymal Stromal Cells and Dermal Fibroblasts The aim of this study was to isolate and characterise equine mesenchymal stromal cells from various sources and to compare their biological properties to that of dermal fibroblasts. By using multiple conventional methods a comparative analysis of the different populations could be made. The results showed that little distinguishes mesenchymal stromal cells from dermal fibroblasts, they have the same morphology and growth characteristics, the same cell surface markers as demonstrated with immunocytochemistry and flow cytometry and the capacity to undergo trilineage differentiation into adipo-, chondro- and osteogenic lineages essentially becoming fat, cartilage and bone. An allogenic synovial fluid model was shown to induce a chondrogenic phenotype in equine mesenchymal stromal cells as well as dermal fibroblasts. A bio-activation assay was performed to evaluate cytokine production of cell populations after activation with Tumour necrosis factor alpha or inflammatory synovial fluid. All of the analysed cell populations demonstrated up-regulation of production of the anti-inflammatory cytokines IL-10 and TGF-β1, after activation with inflammatory synovial fluid, although significant values could not be obtained for every source. As for Prostaglandin E2, results were obtained for bone marrow stromal cells and dermal fibroblasts populations only. Their effects were in opposite; dermal fibroblast reduced the production of Prostaglandin E2 post activation. A functional bio-activation assay has shown promise as a method to distinguish equine mesenchymal stromal cells from dermal fibroblast populations.

year: 2017

title: Making sense of Te Whāriki a te Kōhanga Reo through toi Māori: A whānau approach

authors: McMillan, Hoana

abstract: The involvement of whānau in the teaching and learning process is important at every juncture of a child’s educational journey. Rich understanding of the curriculum enables whānau to make deep and meaningful contributions to discussions about their child’s development. It also presents an interesting challenge for educational settings to create opportunities for whānau to increase their knowledge of the curriculum. This article outlines the benefits of a toi Māori approach to support whānau understanding.

text: Making sense of Te Whāriki a te Kōhanga Reo through toi Māori: A whānau approach The involvement of whānau in the teaching and learning process is important at every juncture of a child’s educational journey. Rich understanding of the curriculum enables whānau to make deep and meaningful contributions to discussions about their child’s development. It also presents an interesting challenge for educational settings to create opportunities for whānau to increase their knowledge of the curriculum. This article outlines the benefits of a toi Māori approach to support whānau understanding.

year: 2023