The Effect Of Acrylic Polymer Dispersions On Water Vapour Permeability And Some Other Physical Properties Of Finished Leathers (PDF/DOC)
The effect of acrylic polymer dispersions on the water vapour permeability and some other properties of finished leathers have been studied. An acrylic based commercial binder AE 558 Nycil has been characterized and its effect when applied in a finish formulation on some of the physical properties of originally retanned leathers was investigated. The binder was found to have an intrinsic viscosity of 227 dL/g, and a viscosity molecular weight (Mv) of 4.03×105. This was obtained by conducting a solution viscosity measurement of the solid polymer in toluene at 25 oC.
The melting temperature of the solid binder has been found to be in the range 361.7 oC – 370 oC. The results of these physical properties suggest that this is a very high molecular weight polymer with high thermal stability. Formulations for leather finishing was prepared containing the binder at varied proportions of 125 g, 150 g, 175 g, 200 g and 250 g and was applied on the leather substrates corresponding to samples A1, A2, A3, A4, and A5 respectively. Tests on some of the physical properties of these coated samples were conducted. The water vapour permeability of the originally retanned (uncoated) leathers was reduced significantly after the finish was applied. A1 has the lowest permeability at 125 g of the binder in the formulation, while A5 has the highest permeability at 250 g of the binder in the formulation.
Generally, the water vapour permeability of the coated leathers increases as the factor varied in this experiment was increased. A3 had the highest Shore A value at 175 g of the binder in the formulation while A5 has the lowest Shore A value at 250 g of the binder in the formulation. Distension and Bursting strength of the uncoated leathers was improved after the leathers were coated. However, there was no particular trend in effect as the quantity of the binder in the finish formulation increased. The fastness of the coated samples generally increased as the quantity of the binder in the finish formulations was increased with sample A5 having the best resistance to wet rub action.
6.0 Conclusion and Recommendations
6.1 Conclusion
The acrylic resin binder is a hard binder with a very large molecular weight, and has a melting temperature in the range 361-370 oC. This shows that the binder is a high polymer and possesses the properties suitable for application in leather finishing. The effect of the resin formulations on some physical properties of the originally retanned leathers have been studied and it is obvious that the finish had significant effect on such properties as water vapour permeability, lastometer, Shore A hardness, and wet rub fastness. The results showed that the finished leathers were better than their unfinished counterpart. Increasing the quantity of the acrylic resin in the formulations also increased the water vapour permeability and wet rub fastness of the finished leathers except for the lastometer tests and shoreA hardness where there was no specific trend in behaviour. All the formulations showed better and adequate response to all the properties tested when compared to that of the unretanned leathers. Sample A1 (125 g resin offer), however would not be suitable for use in leather finish formulations where wet rub fastness is a priority. Aesthetic properties are very important, but finishes must be durable and standards for upper leathers and must include an assessment of finish properties. This has been highlighted in literatures because of the increasing incidence of worn shoe complaints involving lack of finish fastness, and this report has shown that the quantity of components in finish formulations play an important part in determining wet rub resistance. The effect is probably from the resin binder dispersions.
6.2 Recommendations
It is suggested that future development should be aimed at producing components for leather finishes more resistant to water, or means must be found for inactivating the wetting agents present in the finish. While a comprehensive assessment of the effect of all finish components is impossible it is likely that a limited number are of interest to individual tanners who should ensure that new formulations are adequately tested before applying them to bulk production. As finishing plays an important role in water vapour permeability in order to improve the water vapour permeability of leathers, studies should be done on how to improve the water-absorbing capacity of finishing agent. On the other hand, if the water absorbing capacity of finishing agent is too high, the wet rubbing resistance may be decreased. So the work should be done to find a balance to improve the water absorbing capacity without decreasing the wet rubbing resistance
of leathers.
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