Natural rubber is a kind of indispensable biopolymers with great use and strategic importance in human society. However, its production relies almost exclusively on rubber-producing plants
, which ...have high requirements for growth conditions, and the mechanism of natural rubber biosynthesis remains largely unknown. In the past two decades, details of the rubber chain polymerization and proteins involved in natural rubber biosynthesis have been investigated intensively. Meanwhile, omics and other advanced biotechnologies bring new insight into rubber production and development of new rubber-producing plants. This review summarizes the achievements of the past two decades in understanding the biosynthesis of natural rubber, especially the massive information obtained from the omics analyses. Possibilities of natural rubber biosynthesis in vitro or in genetically engineered microorganisms are also discussed.
Summary
Natural rubber (NR) is a nonfungible and valuable biopolymer, used to manufacture ~50 000 rubber products, including tires and medical gloves. Current production of NR is derived entirely ...from the para rubber tree (Hevea brasiliensis). The increasing demand for NR, coupled with limitations and vulnerability of H. brasiliensis production systems, has induced increasing interest among scientists and companies in potential alternative NR crops. Genetic/metabolic pathway engineering approaches, to generate NR‐enriched genotypes of alternative NR plants, are of great importance. However, although our knowledge of rubber biochemistry has significantly advanced, our current understanding of NR biosynthesis, the biosynthetic machinery and the molecular mechanisms involved remains incomplete. Two spatially separated metabolic pathways provide precursors for NR biosynthesis in plants and their genes and enzymes/complexes are quite well understood. In contrast, understanding of the proteins and genes involved in the final step(s)—the synthesis of the high molecular weight rubber polymer itself—is only now beginning to emerge. In this review, we provide a critical evaluation of recent research developments in NR biosynthesis, in vitro reconstitution, and the genetic and metabolic pathway engineering advances intended to improve NR content in plants, including H. brasiliensis, two other prospective alternative rubber crops, namely the rubber dandelion and guayule, and model species, such as lettuce. We describe a new model of the rubber transferase complex, which integrates these developments. In addition, we highlight the current challenges in NR biosynthesis research and future perspectives on metabolic pathway engineering of NR to speed alternative rubber crop commercial development.
Growing American Rubberexplores America's quest during tense decades of the twentieth century to identify a viable source of domestic rubber. Straddling international revolutions and world wars, this ...unique and well-researched history chronicles efforts of leaders in business, science, and government to sever American dependence on foreign suppliers. Mark Finlay plots out intersecting networks of actors including Thomas Edison, Henry Ford, prominent botanists, interned Japanese Americans, Haitian peasants, and ordinary citizensùall of whom contributed to this search for economic self-sufficiency. Challenging once-familiar boundaries between agriculture and industry and field and laboratory, Finlay also identifies an era in which perceived boundaries between natural and synthetic came under review.
Although synthetic rubber emerged from World War II as one solution, the issue of ever-diminishing natural resources and the question of how to meet twenty-first-century consumer, military, and business demands lingers today.
In this research the performance of concrete mixtures incorporating 5%, 7.5% and 10% of discarded tyre rubber as aggregate and cement replacements was investigated. Numerous projects have been ...conducted on replacement of aggregates by crumb rubbers but scarce data are found on cementitious filler addition in the literature. Hence to examine characteristics of tyre crumb-containing concrete, two sets of concrete specimens were made. In the first set, different percentages by weight of chipped rubber were replaced for coarse aggregates and in the second set scrap-tyre powder was replaced for cement. Selected standard durability and mechanical test were performed and the results were analysed. The mechanical tests included compressive strength, tensile strength, flexural strength and modulus of elasticity. The durability tests included permeability and water absorption. The results showed that with up to 5% replacement, in each set, no major changes on concrete characteristics would occur, however, with further increase in replacement ratios considerable changes were observed.
•More than 100 scientific papers published in last 30 years have been reviewed.•Effect of rubber on 12 different mechanical properties have been studied.•Effect of 20 different rubber treatment ...methods have been explored.•Presented comparative graphs on the effect of rubber particle sizes and w/c ratios from the database.•Presented a comparative graph on the effect of various rubber treatment methods from the database.
Recycling of ‘End of Life Tyres’ (ELT) is one of the major environmental concerns faced by the scientific community and the government organisations, worldwide. Every year, an estimated one billion tyres reach their end of life, out of which only about 50% are currently being recycled and the remaining form part of the landfills. Therefore, there is an urgent need to improve the existing and develop new applications of recycled tyre products to address this shortfall in the utilisation rate of the ELT. One application which is actively being researched is the use of waste tyre rubber as a partial replacement of conventional aggregates in concrete applications. Although it shows tremendous potential, it comes with its own challenges such as weak inherent strength of the rubber and poor bond performance with the cement matrix, which hinders its use as an aggregate in large quantities. To overcome this challenge, researchers have looked at various rubber treatment methods that not only improve the bond performance but also significantly improve the mechanical properties of rubber concrete. This review paper considers the effect of rubber particle size, percentage replacement and various treatment methods on different mechanical properties of rubber concrete, studied over the last 30 years. However, to be accepted by the concrete industry, the researchers have to come up with a rubber treatment method that can address the concerns of high flammability and the resultant release of noxious gases from the rubber particles, when exposed to fire.
•Introducing the Recycled Tyre Rubber (RTR) material as environmental problem as well as engineering resource.•Introducing the wet process technology.•Describing in details the existing products ...associated to the wet process high viscosity technology.•Describing in details the wet process No Agitation technology.•Comparing the described technologies and providing justifications and suggestions toward a widespread use of RTR-MBs.
Nowadays, only a small percentage of waste tyres are being land-filled. The Recycled Tyre Rubber is being used in new tyres, in tyre-derived fuel, in civil engineering applications and products, in moulded rubber products, in agricultural uses, recreational and sports applications and in rubber modified asphalt applications. The benefits of using rubber modified asphalts are being more widely experienced and recognized, and the incorporation of tyres into asphalt is likely to increase. The technology with much different evidence of success demonstrated by roads built in the last 40years is the rubberised asphalt mixture obtained through the so-called “wet process” which involves the utilisation of the Recycled Tyre Rubber Modified Bitumens (RTR-MBs). Since 1960s, asphalt mixtures produced with RTR-MBs have been used in different parts of the world as solutions for different quality problems and, despite some downsides, in the majority of the cases they have demonstrated to enhance performance of road’s pavement. This study reports the results of a literature review upon the existing technologies and specifications related to the production, handling and storage of RTR-MBs and on their current applications within road asphalt mixtures. Furthermore, considering that RTR-MBs technologies are still struggling to be fully adopted worldwide, mainly because of poor information, lack of training of personnel and stakeholders and rare support of local policies, the present work aims to be an up-to-date reference to clarify benefits and issues associated to this family of technologies and to finally provide suggestions for their wide-spread use.
The authors have provided a corrected version of Table 1, which can be viewed here. thumbnail Download: * PPT PowerPoint slide * PNG larger image * TIFF original image Table1. Mean elbow angle and ...hand location estimates in respective conditions. https://doi.org/10.1371/journal.pone.0092854.t001 1.
Dating back to the nineteenth-century transplantation of a latex-producing tree from the Amazon to Southeast Asia, rubber production has wrought monumental changes worldwide. During a turbulent ...Vietnamese past, rubber transcended capitalism and socialism, colonization and decolonization, becoming a key commodity around which life and history have revolved. In this pathbreaking study, Michitake Aso narrates how rubber plantations came to dominate the material and symbolic landscape of Vietnam and its neighbors, structuring the region's environment of conflict and violence. Tracing the stories of agronomists, medical doctors, laborers, and leaders of independence movements, Aso demonstrates how postcolonial socialist visions of agriculture and medicine were informed by their colonial and capitalist predecessors in important ways. As rubber cultivation funded infrastructural improvements and the creation of a skilled labor force, private and state-run plantations became landscapes of oppression, resistance, and modernity.Synthesizing archival material in English, French, and Vietnamese, Aso uses rubber plantations as a lens to examine the entanglements of nature, culture, and politics and demonstrates how the demand for rubber has impacted nearly a century of war and, at best, uneasy peace in Vietnam.
•Thorough review on recycling waste rubber tyres (WRT) and properties of WRT products•Recycling WRT products in concrete, asphalt and geotechnical applications•Concerns about toxicity of WRT ...incorporated products due to leaching of chemicals•Inadequate research data on leachate analysis of WRT products for metals and PAHs
Waste tyres and their accumulation is a global environmental concern; they are not biodegradable, and, globally, an estimated 1.5 billion are generated annually. Waste tyres in landfill and stockpiles are renowned for leaching toxic chemicals into the surrounding environment, acting as breeding grounds for mosquitoes, and fuelling inextinguishable fires. The properties of waste tyre rubber and engineering applications have been previously reported in a range of publications with respect to the environmental, economic, and technical factors. This study compiles and reviews this research with a focus on geotechnical engineering applications, such as earthworks and infrastructure construction. The applications of waste rubber in construction materials includes cementitious concrete, asphalt concrete, and granular materials for earth structures. Crumb rubber, when used as a sand replacement in flowable concrete fill, improved ductility and strength-to-weight ratio. A 40 MPa concrete mix with 0.6% rubber crumb content exhibited optimal strength and air entrainment capabilities, displaying minimal damage after 56 freeze/thaw cycles. Rubber, as a partial replacement for aggregate in road base and sub-base layers, adversely affected the California Bearing Ratio (CBR) of the graded aggregate base course. Rubber-soil mixtures as the interface of foundation and structure yielded a 60–70 % reduction in vertical and horizontal ground accelerations when subjected to earthquake simulation modelling. There is concern regarding the toxicity of waste rubber incorporated products due to leachates of heavy metals and other chemicals common in tyres. Further comprehensive studies in this area are needed. Leachate studies should be conducted under different pH and liquid to solid ratios.
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