Posts Tagged ‘Politics’

Polyurethanes, Polymers and Sports Balls

April 13th, 2022

The rubber ball must be the earliest use of polymers in sport, obviously being known to the inhabitants of South America when Europeans first crossed the Atlantic. It is a longtime since golf balls were made of anything other than polymers; the wound rubber ball as early as 1898. The ‘classic’ construction of the three-part golf ball is a complicated process; poly isoprene thread is wound over a small solid rubber core and the cover formed from balata or polyurethanes. The solid or two-part ball has a solid rubber core with a polyurethane cover and can be compression or injection molded.

One-part balls can be of rubber or polyurethane but the ideal performance characteristics cannot be achieved by this construction and they are used by beginners to practice and on driving ranges. The conflicting requirements for a golf ball (speed and distance through the air, behavior on the ground, control of spin and toughness) mean that all properties cannot be optimized in one design. Generally, the three-part ball gives better control at the expense of distance for given power input. As well as the materials, the design of the dimpled cover is critical to performance. Development of the golf ball is limited to a great extent by the laws enforced by the sport’s governing body. If balls which could travel significantly further were allowed, the golf courses, which represent large investment, would appear too small.

The aerodynamic design is also limited by the requirement for it to be symmetrical. This has not stopped there being intense competition between manufacturers and continuing efforts to improve. A recent development has been tungsten filler which partly reduces the amount of traditional fillers. Tennis balls also require specialized production techniques and are again regulated by a specification. The bounce characteristics of pressurized tennis balls are dependent on the internal pressure, which is typically 100 kPa above atmospheric. As air permeates out, the pressure drops and the playing characteristics change.

The loss can be reduced by filling with a gas that permeates more slowly than air or by using an elastomer with lower permeability. Special containers manufactured from such materials as acrylonitrile-butadiene-styrene are produced to maintain the pressure of gas-filled balls. Un-pressurized balls rely on the material which forms the wall (such as butadiene) to provide the necessary resilience. Titanium has been added to the rubber compound to improve performance. The traditional leather football became very heavy when wet and quality was very variable. Balls made from polyvinyl chloride, ethylene vinyl acetate or polyurethane will be much more consistent, and where leather is used it is coated with an elastomer to prevent water absorption. However, the characteristics can vary according to the material and construction used and a survey back in 1985 found that a range of balls all complying with the regulations varied by 15% in resilience. Molding the shell of a ball on to which the exterior panels are attached means it can have an integral bladder. Polyurethane appears to have become the most usual material and one innovation incorporates a cellular structure. Balls for basketball, handball and softball are essentially similar to those for football.

A polymeric coating on high-class rugby balls improves the grip in wet conditions. Squash balls are of relatively simple construction being basically rubber moldings. However, the formulations used may be complex and very specialized and are jealously guarded. Different formulations are used to produce a range of balls with different speed characteristics to suit the various levels of skill which exist in the sport, or which will not mark surfaces against which they are hit. Polymers have found it very difficult to oust the traditional cricket ball but molded polyvinyl chloride balls are used at lower levels. Bowling balls, bowls, croquet balls, table tennis balls and many others are produced from various plastics. There are even rubber or polyvinyl chloride medicine balls, polypropylene rounder balls, foam balls resembling tennis balls, glow balls, perforated plastic balls and Koosh balls in natural rubber. Should you require it, there is a see-through Budweiser bowling ball in polyester which contains a replica of a Bud bottle. Shuttlecocks are used in roughly the same way as a ball.

A method of making plastic shuttlecocks by an advanced injection process whereby the polyamide skirt is fully formed in the mold has been reported which is claimed to yield a product closer to the traditional hand-built feather designs than until now. The ball is not the only item of essential equipment needed to play most ball games. There are also bats, racquets, sticks, goalposts, nets, etc. As with the balls, there are limits imposed by the rules of the games but there is enormous potential for innovative design using polymers. Tennis and squash racquets have been revolutionized by polymers with the introduction of advanced composites. After laminate construction replaced solid wood, metal tennis rackets took over in the 1970s but now fiber reinforced composites are universally used. The earlier rackets used glass fiber reinforced polyester but now more advanced composites with carbon and boron fibers have been introduced with high modulus carbon fiber being standard. The advantages are based on the stiffness to weight ratio and the control of the racket’s characteristics which can be achieved through geometry of the reinforcement. Also, composites have better fatigue resistance and higher damping. Other parts of the racket also utilize polymers: polyamide bumper guards, polyamide and polyester strings and rubber grips. Composites also compete with metals in the construction of golf clubs. Fiber reinforced shafts are produced by winding pre-preg onto a steel mandrel which is later removed.