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Leather is made of collagen protein polymer, which is used in the manufacture of a variety of products including footwear, automotive upholstery, garments, and sports equipment. Animal skins/hides are converted into leather using a series of chemical processes. Of them, the tanning process is the most important chemical process that converts animal skins into leather by stabilising collagen fibre so that they do not putrefy. However, it is a hazardous process because of the use of various toxic chemicals in tanning, re-tanning and fatliquoring treatments producing toxic effluent. Over the years many tanning treatments based on chromium sulphate, and vegetable and synthetic tannins in combination with heavy metals, have been developed but tanning with chromium sulphate (known as Cr-tanning) is still the most effective, cheap, and widely used tanning process in the leather industry. Although the development of various improved Cr-tanning methods highly reduced the chemical and water consumption in leather tanning, it is still under scrutiny because of the production of effluent containing a harmful level of Cr and there is strong evidence that when the treated leather is disposed into the environment, part of the released trivalent chromium is converted into carcinogenic hexavalent chromium. Many sustainable alternatives to Cr-tanning based on chemical and enzymatic crosslinking, various bio-derived polymers, enzymes, modified zeolites, and nanostructured materials have been developed over the years with limited success. The alternative methods are either not as effective as Cr-tanning, affect the dyeability and other functional and organoleptic properties of leather, and or are cost-prohibitive. In this comprehensive review article, various tanning methods used in industry or studied in the laboratory are critically reviewed, and their advantages and disadvantages are outlined. The consumption of tanning agents, total chemicals including various auxiliaries and fatliquoring agents, and water in tanning, and the tanning performance and mechanical properties of the processed leather are compiled and compared. The reaction mechanisms of novel tanning agents with leather collagens and the future directions to make leather tanning more sustainable are outlined. This review article will be a guide for academicians/researchers/manufacturers involved in leather processing to develop more sustainable leather materials. [ABSTRACT FROM AUTHOR]

Elastomeric composites based on Ethylene-Propylene-Diene-Monomer (EPDM) filled with multi-wall carbon nanotubes (MWNTs) have been prepared, showing improved mechanical properties as compared to the pure EPDM matrix. The results have been discussed using the Guth model. The main focus of the study was on the electrical behavior of these conductive polymer composites (CPCs), in view of possible sensor applications. A linear relation has been found between conductivity and deformations up to 10% strain, which means that such materials could be used for applications such as strain or pressure sensors. Cyclic experiments were conducted to establish whether the linear relation was reversible, which is an important requirement for sensor materials. [ABSTRACT FROM AUTHOR]

This article discusses a study on the use of microstructural finite element models investigating the modulus of filled elastomer over a wider range of strains than has been possible previously. This study offered insight into rigid filler reinforcement and the filler interaction mechanisms. The study considered medium thermal (MT)-type carbon-black filled rubber behavior due to the large amount of experimental data available in the literature.

The introduction of dynamic bonds capable of mediating self-healing in a fully cross-linked polychloroprene network can only occur if the reversible moieties are carried by the cross-linker itself or within the main polymer backbone. Conventional cross-linking is not suitable for such a purpose. In the present work, a method to develop a self-healable and recyclable polychloroprene rubber is presented. Dynamic disulfide bonds are introduced as part of the structure of a crosslinker (liquid polysulfide polymer, Thiokol LP3) coupled to the polymer backbone via thermally initiated thiol-ene reaction. The curing and kinetic parameters were determined by isothermal differential scanning calorimetry and by moving die rheometer analysis; tensile testing was carried to compare the tensile strength of cured compound, healed compounds and recycled compounds, while chemical analysis was conducted by surface X-ray Photoelectron Spectroscopy. Three formulations with increasing concentrations of Thiokol LP-3 were studied (2, 4, 6 phr), reaching a maximum ultimate tensile strength of 22.4 MPa and ultimate tensile strain of 16.2 with 2 phr of Thiokol LP-3, 11.7 MPa and 10.7 strain with 4 phr and 5.6 MPa and 7.3 strain with 6 phr. The best healing efficiencies were obtained after 24 h of healing at 80 °C, increasing with the concentration of Thiokol LP-3, reaching maximum values of 4.5% 4.4% 13.4% with 2 phr, 4 phr and 6 phr, respectively, while the highest recycling efficiency was obtained with 4 phr of Thiokol LP-3, reaching 11.2%. [ABSTRACT FROM AUTHOR]

Modelling the viscoelastic behavior of rubber for use in component design remains a challenge. Most of the literature does not consider the typical regimes encountered by anti-vibration devices that are deformed to medium dynamic strains (0.5 to 3.5) at medium strain rates (0.5/s to 10/s). Previous studies have either focused on the behaviour at small strains and small strain rates or in fast loading conditions that result in low cycle fatigue or tearing phenomena. There is a lack of understanding of the dynamic response of natural rubber suspension components when used in real vehicle applications. This paper presents a review of popular viscoelastic nonlinear constitutive models and their ability to model the mechanical behaviour of typical elastomer materials such as Natural Rubber (NR) incorporating different PHR (Parts per Hundred Rubber, XX) of carbon black. The range of strain and strain rate are typical for the materials used in rubber suspensions when operating in severe service operating conditions, such as over rough terrain or over pot-holes. The cyclic strain is applied at different amplitudes and different strain rates in this medium strain range. Despite the availability of many models in the literature, our study reports that none of the existing models can fit the data satisfactorily over a wide range of conditions. [ABSTRACT FROM AUTHOR]

This report presents an evaluation of thiyl radical-induced cis / trans isomerism in double bond-containing elastomers, such as natural, polychloroprene, and polybutadiene rubbers. The study aims to extensively investigate structural changes in polymers after functionalisation using thiol-ene chemistry, a useful click reaction for modifying polymers and developing materials with new functionalities. The paper reports on the use of different thiols, and cis / trans isomerism was detected through 1 H NMR analysis, even at very low alkene/thiol mole ratios. The study finds that the configurational arrangements between non-functionalised elastomer units and thiolated units followed a trans -functionalised- cis units arrangement up to an alkene/thiol mole feed ratio of 0.3, while from 0.4 onward, a combination of trans -functionalised- cis and cis -functionalised- trans configurations are found. Additionally, it is observed that by increasing the level of functionalisation, the glass transition temperature of the resulting modified elastomer also increases. Overall, this study provides valuable insights into the effects of thiol-ene chemistry on the structure and properties of elastomers and could have important implications for the development of new materials with enhanced functionality., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)