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Mechanical Properties of the 100% Recycled and Virgin PP Fibres

As shown in Fig. 4.7, the 100% recycled and virgin PP fibres produced by same melt spinning and hot drawing process, have same geometry and dimensions (1.5 mm in width, 0.7 mm in thickness, and 47 mm in length).

A brittle mode of failure was seen in both fibres (Fig. 4.8), with a short elastic phase of steep slope and a progression of sharply rising stress until fracture. The averages of the tensile strength, Young’s modulus based on 30 specimens for each fibre type are shown in Table 4.4 as well as the elongation at break and their standard deviation. As can be seen, the 100% recycled PP fibre shows lower tensile strength (284.1 MPa) but much higher Young’s modulus (4582 MPa) than those of virgin PP fibre. According to the research in Chap. 3, the 100% recycled PP fibre has lower molecular weight and shorter molecular chains than those of virgin PP fibre. The shorter molecular chains make the recycled PP fibre easier to be crystallised, thus producing higher Young’s modulus. However, the shorter molecular chains have less molecular entanglement and hence, lower tensile strength.

a 100% recycled and b virgin PP fibres

Fig. 4.7 a 100% recycled and b virgin PP fibres

Typical stress-strain curves of PP fibres

Fig. 4.8 Typical stress-strain curves of PP fibres

Table 4.4 Mechanical properties of PP fibres

Tensile stress (MPa)

Young’s Modulus (MPa)

Elongation at break (%)

Average

Standard

deviation

Average

Standard

deviation

Average

Standard

deviation

Virgin PP fibre

356.4

30.6

3129

564

12.6

2.8

100% recycled PP fibre

284.1

21.0

4582

1661

6.2

2.2

 
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