Page 345 - Biodegradable Polyesters

13.2 Reinforcements in Polymer Composites 323

that remain distinct and separate within the produced structure. Here we briefly
describe three types of fiber reinforcements, glass or carbon fibers, natural fibers,
and synthetic fibers for fiber-reinforced polymer (FRP) composites. The reinforce-
ment fibers are usually carbon, glass, or aramid, while other fibers such as paper,
flax, jute, bamboo, wood, or asbestos have also been used. The aim is typically
to create a component which is strong and stiff, usually with a low density and
improved functional properties. Conventional composites usually have glass or
carbon fibers in a matrix based on a thermosetting or thermoplastic polymer [6].
There are supplementary classes of composite in which the matrix is a metal or a
ceramic. But these are suited to specific applications and may involve high produc-
tion costs. In addition, in these composites the motives for adding the fibers are
often to enhance functional properties, such as creep, wear, fracture toughness,
fatigue, and so on.
13.2.1
Glass and Carbon Fiber Reinforcements

The utility of FRP composites, with glass and carbon fiber reinforcements, has
been growing at a remarkable rate as these materials are increasingly used in
their current applications. There is a growing trend to establish their use in
novel products in relatively new areas such as biomedical applications [7]. A key
factor motivating the increased applications of FRP composites over the current
years is the progressive development of new forms of glass/carbon FRP materials
[8]. This embraces developments in high-performance resin systems and new
types of strengthening agents, such as carbon nanotubes and nanoparticles. The
polymers are typically epoxy, vinyl esters, or polyester thermosetting plastics,
and phenol-formaldehyde resins.
FRPs are frequently used in the automotive, aerospace, marine, and construc-
tion industries [9]. Considering a specific case, woven glass fibers were reinforced
in acrylic polymer [10] for denture applications. The mechanical properties [11]
such as flexural strength, flexural modulus, and impact strength were significantly
enhanced owing to the presence of glass fibers; however, the manufacturing these
composites is not economically viable [12]. Carbon fiber reinforced polymer
(CFRP) [13] composites provide good energy absorption efficiency under high-
velocity impact loading [14]. The specific impact toughness can even be higher
than that of 304 stainless-steel. These glass/carbon fiber composites suffer from
the disadvantage of being noneconomical and nonecofriendly when used with
common (nonbiodegradable) polymers. For example, the composites treated with
hexavalent chromium can be categorized as harmful waste and thus may not be
disposed on land owing to potential discharge of the chromium into the ground.

13.2.2
Natural Fiber Reinforcements

Numerous types of natural fibers (such as flax, jute, sisal, coir, and hemp) have
been used as reinforcements in polymer composites for various engineering