*Waste Material Recycling in the Circular Economy - Challenges and Developments*


**Table 3.**

*Reliability data after thermal cycling.*

*Effect of heat soak on (a) tensile strength, (a) tensile strain and (c) life distribution of virgin PC, 50% PCR and 75% PCR.*

*Effect of Environmental Aging on Tensile Properties of Post-Consumer Recycled (PCR)… DOI: http://dx.doi.org/10.5772/intechopen.99528*


**Table 4.**

*Reliability data after high temperature and high humidity.*

life, Weibull *α* and Weibull β are very similar for Virgin PC, 50% and 75% PCR respectively [9, 10].

But when the humidity is added to the temperature absolute humidity (gm/m<sup>3</sup> ) increases from 25.63 gm/m3 (for 60<sup>o</sup> C - 20% RH) to 115 gm/m<sup>3</sup> (for 60<sup>o</sup> C - 90% RH) then the aging effect is more pronounced. The effect in aging is clearly visible in **Figure 7(a)** and **(b)** by the decrease in tensile strength and tensile strain at breakage for all the three grades of PC and PCR. But most importantly, both virgin PC and two grades of PCRs were found to have similar aging behaviors. Literature shows that the molecular weight reduces due to the hydrolysis of carbonate groups [11–15], which leads to the decrease of the tensile strength [16–18]. Prolonged exposure to high heat and humidity eventually induces a ductile to brittle transition [19]. The reduction in tensile strength and ductility are consistent with environmental degradation. Other mechanisms discussed in literature include a decrease in molecular weight due to hydrolysis and formation of small, disk-shaped microcavities or microcracks [11, 14, 15] that cause reduced strength and elongation. In this manuscript, the dominant mechanism has not been verified. In the fractography section, the fracture surface of the unaged and aged samples was analyzed to see whether this hypothesis is in line with the observed features for both conventional PC and PCR grades.

When we take these data into account and model the reliability of destructive degradation (**Figure 7(c)**), we found a comparable B10 (where 10% unit fails) value between virgin PC and two grades of PCR PC after thermal cycling aging. In temperature- and humidity-exposure, the B10 value is understandably lower than the temperature cycle aging but more importantly, virgin PC and PCR show comparable B10 and Weibull alpha values (**Table 4**).
