Polymers in Sport and Leisure

Polymers in Sport and Leisure
characteristics of pressurised 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.
Unpressurised balls rely on the material which forms
the wall (such as butadiene (310)) to provide the
necessary resilience. Titanium has been added to the
rubber compound to improve performance (174).
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. Moulding 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 (186). Balls for basketball, handball
and softball are essentially similar to those for football.
A polymeric coating on high-class rugby balls enhances
the grip in wet conditions.
Squash balls are of relatively simple construction being
basically rubber mouldings. However, the formulations
used may be complex and very specialised 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 moulded 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
rounders 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 (2).
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 mould has been reported (366)
and which is claimed to yield a product closer to the
traditional hand-built feather designs than hitherto.
The ball is not the only item of essential equipment
needed to play most ball games. There are also bats,
racquets, sticks, goal posts, nets, etc. As with the balls,
there are restrictions imposed by the rules of the games
but there is enormous potential for innovative design
using polymers.
Tennis and squash racquets have been revolutionised
by polymers with the introduction of advanced
composites. After laminate construction replaced
solid wood, aluminium tennis rackets took over in
the 1970s but now fibre reinforced composites are
universally used. The earlier rackets used glass fibre
reinforced polyester but now more advanced
composites with carbon, aramid and boron fibres
have been introduced with high modulus carbon fibre
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 utilise
polymers: polyamide bumper guards, polyamide and
polyester strings and rubber grips.
Composites also compete with metals in the
construction of golf clubs. Fibre reinforced shafts are
produced by winding prepreg onto a steel mandrel
which is later removed. An alternative is to use an
injection-moulded core, which is retained. Various
designs of fibre reinforced epoxy club heads have been
produced as well as metal heads with fibre reinforced
plastic inserts. By injecting a thermoplastic into a
hollow head, weight can be added preferentially in
given areas.
A composite-modified wood baseball bat for
professional use which uses carbon and Kevlar
composites has recently been patented (43), although
a similar product has also been reported (18).
Polymers find use in many ancillary products from net
bags to carry balls to glass reinforced plastic
backboards to basketball goals. Golf trolleys are
essential for some people and are yet another outlet
for polymers. One example uses nylon for the chassis,
gear housing from glass reinforced polyethylene
terephthalate, and nylon and acetate homopolymer for
the gears (397). A transparent top for a golf cart has
been made from polyester and an irons organiser from
nylon (72).
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