Colouring of Polymers and Composites - Introduction to Polymeric Composites with Rice Hulls - page 101

8 Colouring of Polymers and Composites
8.1 Introduction
Although synthetic materials are man-made, it is not unreasonable to think that they
are in harmony with nature. Rice hulls, wood and other cellulose-based constituents
in a well-balanced blend with synthetic plastics resins are known as polymeric
composites with rice hulls (PCRH) and wood plastic composites (WPC), respectively.
WPC have been around for some time, particularly in applications such as decking
and fencing, but perhaps the importance of coloured products may not have been
significant. Now, with the advent of PCRH in a wider range of applications (e.g.,
outdoor; indoor; building construction; furniture; automobile parts; and sportswear),
coloured products are of immense importance. Therefore, designers, developers and
producers of polymeric composites must have at least a basic knowledge of colour.
This is a speciality area and there are many manufacturers and suppliers from whom
ready-made colourants can be purchased. The trend with WPC producers has been
in-house experimentation with various combinations for composites, and this will be
even more so for PCRH with a wider range of applications. Thus, a basic knowledge
of colouring, blending and methodology will be of tremendous value to improve
products but cost-effectiveness will also be a key factor.
Colourants can be ranked according to their tone; pigment class; colour index; opacity;
light-fastness; tinting strength; and physiological/chemical properties. Unlike pigments,
colourants are soluble in plastics. Manufacturers of colourants try to maintain
equilibria between natural and synthetic materials and, other than the many standard
ones available, most manufacturers offer custom-made services to meet any type of
colour and properties required. With advances in the technology of masterbatch
colouring, additive masterbatches (i.e., the required additives, for example, anti-
ultraviolet (UV) agents) and flame retardants are incorporated into masterbatches.
8.1.1 Theory of Colours
Using colours, one can set a mood, attract attention or make a statement. One can
use a colour(s) to energise or to cool down. By choosing the right colour scheme,
one can create an ambiance of elegance, warmth or tranquility. Colour can be the
most powerful design element in a final product if one knows how to it effectively.