Polymers 2022 , 14 , 3309
15of 18
Figure8. Drainage time, filler content and filler retention as a function of dosage of the best floccu- lants. For the suspension with only pulp and PCC (reference test), the drainage time was 1.59 s. From the target filler content of 20 wt %, only ca. 43% was retained during drainage (less than half the added amount), resulting in an effective final filler content of 8.6 wt %. With the addition of CPAM (1 mg/g of PCC), the filler retention increased to ca. 73%, corresponding to a filler content of 14.5 wt % (an increase of ca. 70% versus the reference). As a consequence of the increased retention, an increase in the drainage time to 1.65 s was also observed. For both CCs, an increase in filler retention was always detected, which retention directly improved with the level of addition. Nevertheless, none of the formulations led to better retention than that of CPAM. Sample GT0.16_F led to a better filler retention than sample CH0.13_F at 54.8, 58.7 and 61.6% against 45.8, 49.6 and 60.7%, for an addition of 0.02, 0.2 and 0.4 wt %, respectively. In terms of drainability, sample CH0.13_F, always presented drainage times that were lower than the reference and that decreased with the increase in the addition level, with a reduction of ca. 7% to 1.48 s for the highest dosage. For sample GT0.16_F, the drainage times remained slightly higher than the reference. The decline in the drainage time observed for sample CH0.13_F when higher dosages were used can be explained by the excessive tendency of this sample to flocculate (as observed by LDS), promoting the formation of large and porous flocs of fibers. These big flocs can result in the heterogeneity of the pad, which leads to regions with fewer fibers that promote preferential drainage channels and a consequent decrease in the drainage time. The existence of these channels may also favor the loss of small PCC flocs that are not properly stuck to the fiber network, which may explain why the structure of sample CH0.13_F, although demonstrating a higher flocculation performance than GT0.16_F in the LDS flocculation tests, did not translate into improved filler retention.
Made with FlippingBook - Online magazine maker