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Shelf Life Estimation for Water based Paints with Regression Methods

Obidi Olayide F, Nwachukwu Simon C, Aboaba Olusimbo O, and Nwalor John U

The shelf lives of water-based paints made in Nigeria were investigated. The mean changes in the microbial population count of six freshly made paint samples (PS1 – PS6) were monitored fortnightly for a period of 10 months. The growth data of isolated organisms from the fresh and spoilt paint samples were fitted into a multiple linear regression model to predict shelf life for the fresh paint samples. The microbial population ranged from 1.0 x 101 – 4.7 x 105 cfu/ml and from 1.0 x 101 – 5.5 x 103 cfu/ml for bacteria and fungi over the study period. Physico-chemical parameters such as specific gravity (SG), optical density (OD), transmittance (TR), pH and viscosity (VIS) were also determined every two weeks for the fresh paint samples over the ten-month study period. The measurements of the physico-chemical parameters suggested deterioration related to microbial population count of the paint samples. Consequently, the model developed comprised of two equations with particular attention to microbial population count and physico-chemical parameters of the paint samples. The microbial population counts of the spoilt paint samples were 3.4 x 1010 cfu/ml and 3.2 x 105 cfu/ml for bacteria and fungi respectively. The changes in the physico-chemical parameters ranged from 2.8658 – 1.0853, 1.49 – 3.91, 6.9 – 2.3, 8.5 – 5.6, 11.7cst –10.8cst for SG, OD, TR, pH and VIS in fresh paint samples. The percentage residual error between the shelf life predicted and the shelf life experimental ranged between 0.001 and 0.500. The shelf lives obtained for the fresh paint samples were 19, 21, 23, 22, 37, and 22 months respectively.