Page 226 - Materials Chemistry, Second Edition

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Recycling of Municipal Solid Waste Rejects
is less than that observed in the mixes prepared at a temperature of 185°C.
However, a 60% sand concentration prepared at 240°C revealed a volume
fraction of voids of 7% which is higher than that observed in the mixes pre-
pared at 185°C. For more details see Abou Khatwa et al. (2005). A comparison
between samples prepared at a temperature of 185°C and 240°C revealed a bet-
ter mix homogeneity for the high mixing temperature. The dispersion of the
sand particles in the polymer matrix was enhanced and there were fewer areas
of polymer segregation in the composite material. In addition, polymer segre-
gation was much more pronounced in mixes containing high sand concentra-
tions as observed by the scanning electron micrographs of these segregated
polymeric phases. It can also be observed that weak interfacial bonds existed
between the segregated areas and the polymeric matrix as revealed from the
inclusions present around the segregates. Moreover, the incomplete melting
of the recycled rejects can also be observed, which resulted in lack of diffusion
between the fragmented plastic wastes.

Mechanical properties
Compressive strength
The compressive properties for all the mixes as shown in Table 6.2 were
evaluated using the standard test method ASTM D 695M-91 (1998). The
compressive strength values in this case can only be used as an indication of
the stability of the material investigated.
The average compressive strength values ranged between 10.2 and
22.2 MPa at a strain of 0.1. Mix 3 (60% sand, sieve 1, and temperature 185°C),
mix 6 (60% sand, sieve 2, and temperature 185°C), mix 9 (60% sand, sieve 1,
and temperature 240°C), and mix 12 (60% sand, sieve 2, and temperature

TABLE 6.2
Mechanical Properties of Prepared Mixes (Abou Khatwa et al., 2005)
Mix no. Compressive Flexural Shore D
strength (MPa) strength (MPa) hardness no.
Mix 1 10.154 12.241 58.28
Mix 2 11.897 11.184 63.37
Mix 3 15.622 10.447 66.20
Mix 4 12.821 15.191 59.43
Mix 5 15.502 11.307 64.17
Mix 6 16.478 10.725 68.53
Mix 7 10.992 16.463 60.40
Mix 8 13.125 21.239 67.73
Mix 9 20.250 11.260 68.80
Mix 10 13.122 13.550 61.88
Mix 11 17.981 16.345 69.12
Mix 12 22.247 13.936 69.87