Polybutadiene: A Versatile Synthetic Rubber
Introduction
Polybutadiene, commonly referred as butadiene rubber or BR, is a synthetic rubber produced from polymerization of the monomer 1,3-butadiene. Polybutadiene was first synthesized in the early 1930s and found applications in automobile tires shortly after. Today, polybutadiene remains an important type of synthetic rubber due to its excellent flexibility, resilience and resistance to wear and aging. In this article, we will discuss the production, properties and various applications of this versatile synthetic rubber.
Production of Polybutadiene
Polybutadiene is commercially produced by the process of emulsion polymerization, where butadiene monomer, emulsifiers and catalysts are mixed and reacted in an emulsion system. The commonly used catalysts include lithium, sodium and potassium based initiator systems. Polymerization is carried out at temperatures between 50-90°C for 1-4 hours resulting in formation of polybutadiene particles suspended in water. The product is then separated by centrifugation and dried under vacuum. Based on the type of microstructure formed during polymerization, polybutadiene is classified into three types - high cis-1,4 polybutadiene (>90%), high trans-1,4 polybutadiene (>90%) and random or low cis-1,4 polybutadiene (30-70%). The properties and applications vary significantly based on the microstructure.
Properties and applications of polybutadiene
The properties of polybutadiene are highly dependent on the microstructure type produced during polymerization. High cis-1,4 polybutadiene exhibits excellent flexibility, resilience and strength making it ideal for applications requiring high elasticity and wear resistance. Around 90% of all polybutadiene production is used in manufacturing of automobile tires due to its unmatched ability to withstand wear under cyclic flexing and deformation. Apart from tires, high cis-polybutadiene also finds applications as impact modifiers in plastics, footwear, hoses and belts.
On the other hand, high trans-1,4 polybutadiene has a stiff, rigid structure resulting in high tensile strength but poor flexibility. It is primarily used as a modifier in styrene-butadiene rubber (SBR) blends to impart strength and reduce costs. Random or low cis-polybutadiene exhibits an intermediate set of properties. It has greater stiffness compared to high cis-polybutadiene but better flexibility than high trans-type. Therefore, it finds limited uses in applications requiring a balance between modulus and elasticity like gaskets, seals and adhesives.
Future prospects and conclusions
Global demand for Polybutadiene is expected to grow steadily at around 3-4% per year, primarily driven by the continuously expanding automobile industry worldwide. Tire manufacturers are working towards developing improvedPolybutadiene formulations to enhance tire performance parameters like rolling resistance, wet traction and wear rate. Polybutadiene producers on the other hand are focusing their R&D efforts on developing manufacturing technologies to optimize product microstructure control and improve process efficiency. New applications of polybutadiene are also emerging in areas such as footwear soles, polymers modified with polybutadiene and high performance rubber products. With its excellent balance of properties and economical production, polybutadiene is anticipated to remain a workhorse elastomer for the rubber industry.
Environmental impact of polybutadiene production
While polybutadiene offers advantages over natural rubber in terms of properties and performance, its production does pose some environmental concerns that need to be addressed. The butadiene monomer used is a hazardous air pollutant and its polymerization emits volatile organic compounds (VOCs) that are greenhouse gases. Improper disposal of polybutadiene waste can also cause pollution issues. Manufacturers have implemented various techniques like utilizing non-solvent systems, recovering unreacted monomers, incinerating waste and end-of-life tire recycling to reduce the environmental footprint. Still, further improvements are required to make polybutadiene production a more sustainable process. Research on developing “green” catalysts that allow polymerization without generating VOCs can significantly lower the carbon footprint of this important synthetic rubber.
Polybutadiene has emerged as one of the most widely consumed synthetic rubbers owing to its excellent balance of properties, cost-effectiveness and performance advantages over natural rubber. Around two-thirds of total polybutadiene production still goes into tire manufacturing. New applications continue to evolve leveraging its high resilience, flexibility and strength. While polybutadiene manufacturing methods need optimizing from an environmental perspective, ongoing R&D ensures this synthetic rubber remains indispensable for the rubber industry. Sustainable production practices coupled with superior product formulations will enable polybutadiene to stay highly relevant in the future.
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