Durability of plastic products

Many external factors can break down plastics: ultraviolet and visible light, heat, cold, mechanical stress, wind, snow, hail, ice, acids, ozone and other air pollutants, water and other liquids, micro-organisms, animals and plants. The lifespan of plastics is extremely variable, depends

Table 9.11 The anticipated lifespan of plastics

(Sources: Grunau, 1980; Holmstrom, 1984).

Table 9.11 The anticipated lifespan of plastics

(Sources: Grunau, 1980; Holmstrom, 1984).

Type

Assumed lifespan (years)

Butyl rubber IIR

2-less than 35

Chloroprene rubber CR

2-less than 40

Ethylene propylene rubber EPDM

Less than 30

Ethylene vinyl acetate EVA

3

Melamine formaldehyde MF

6-10

Phenol formaldehyde PF

16-18

Polyamide PA

11-less than 30

Polyethylene PE

2-151

Polyisobutylene PIB

11-less than 40

Polymethyl methacrylates PMMA

Less than 40

Polypropylene PP

3-less than 10

Polysulphide rubber T

22-less than 50

Polytetrafluor ethylene PTFE

25-less than 50

Polyurethane PUR

7-10

Polyvinyl chloride PVC

8-less than 301

Silicone rubber SR

14-less than 50

Styrene butadiene rubber SBR

8-10

Urea formaldehyde UF

5-less than 35

Notes: Includes both external and internal use. Positioning in water or earth is not included. The most protected locations achieve the best results. 1 Does not apply to buried cold water pipes in thicker plastic, which is assumed to last longer. (Sources: Grunau, 1980; Holmstrom, 1984).

Notes: Includes both external and internal use. Positioning in water or earth is not included. The most protected locations achieve the best results. 1 Does not apply to buried cold water pipes in thicker plastic, which is assumed to last longer. (Sources: Grunau, 1980; Holmstrom, 1984).

on its type, its position and the indoor or outdoor temperatures and climatic conditions it is exposed to (Table 9.11).

Plastic products are used in floors, roofs and walls in such a way that it is often difficult and expensive to repair or replace them. They should therefore have a functional lifespan equivalent to other materials in the building; at least 50 years. It is unlikely that most of today's plastics can satisfy such conditions.

Although many plastics have been on the market for over 25 years, new mixtures, additives and modifications are often being introduced. This has often been in order to phase out environmentally problematic constituents. Amongst polymer technicians it is well known that today's plastic products are very different from those on the market only a few years ago. It is therefore difficult to prove the durability of existing products.

The assumed lifespan of a product is usually based on so-called accelerated ageing tests. The material is exposed to heavy, concentrated stresses and strains over a short period. In the early 1980s, Dr K. Berger from the plastics manufacturers Ciba Geigy AG stated that present forms of accelerated ageing test had a 'low level of accuracy at all levels' (Holmstrom, 1984). Testing methods have not changed much since then, and the picture has not been made easier by the fact that new additives are constantly appearing. It is also recognized that we still do not fully understand the effects of different climate conditions (Shokrieh etal., 2007). PVC is considered to be a plastic with good durability, but it has been known to undergo very rapid breakdown. In Sweden, 10-year-old plastic skirtings crumbled not because of the PVC itself but because of an added compound, acrylonitrile butadiene styrene (ABS), which should have increased the strength and durability. ABS plastics oxidize easily.

Sealing strips of ethylene propylene rubber (EPDM) are often used between elements in prefabricated buildings of timber and concrete. Research has shown that certain types have lost elasticity after as little as only one year. This means that the joint is no longer sealed and the construction no longer functions.

It is very common to tape plastic foils and other plastics-based layers that form the important airtightness or damp proof membranes in buildings. This can be in most areas: walls, roofs, around openings, etc. It has been shown repeatedly, however, that these tape materials can both become brittle themselves, and decay the plastics, quite quickly, with dramatic consequences (Adalbert, 1998).

0 0

Post a comment