Selection And Application Studies On The Defoamers Used For Removing The Foam On Partially Alcoholyzed PVA Paste

The foam produced by partially alcoholyzed PVA pastes not only induces great difficulty to sizing operation,but also make it difficult to control sizing production.The foam leads to sizing defects like uneven sizing and reduces the quality of sized yarns.In order to solve the problem of the foam by partially alcoholyzed PVA,this study utilized defoaming agents to remove the foam and eliminated the adverse influence of the foam on warp sizing.The main aim of this research was focused on the selection of defoamers that were suitable for eliminating the foam existing on partially alcoholyzed PVA pastes.Another aim was to break the monopoly of Japanese 205 MB in the market of low degrees of polymerization and alcoholysis for filling in the blanks of China.The defoamers were selected in terms of the defoaming characteristics(defoaming time and defoaming rate),paste viscosity,adhesion-to-fibers,surface tension,contact angle,film properties,properties of sized yarn,and desizability.They were evaluated and choosen according to the defoaming ability and the effect of defoamers on the sizing performances of partially alcoholyzed PVA.The defoamers investigated included monohydric alcohol,organic silicon,sodium stearate,wax,and composited defoamers.The adhesion of partially alcoholyzed PVA to fibers was measured with a roving method based on FZ/T 15001-2008 standard regulated by China Cotton Textile Association.Mechanical properties of sizing films were determined according to ASTM-D-882 international standard.Mechanical properties of raw and sized yarns were tested in accordance with ASTM-D-2256 international standard.Abrasion resistances of raw and sized yarns were measured according to FED-STD-191-4308 international standard.Desizability was evaluated via an alkaly-oxidant desizing.The defoaming ability of monohydric alcohol defoamers to partially alcoholyzed PVA paste was evaluated.The effect of chain-length of alkyl in monohydric alcohol on the defoaming for partially alcoholyzed PVA was examined.The influence of the chain-length upon the end-use ability of partially alcoholyzed PVA was revealed.And suitable dosage of monohydric alcohol defoamer was supplied by means of experiments.It was found that the chain-length of alkyl in monohydric alcohol showed significant effects on the defoaming of the defoamers to partially alcoholyzed PVA.As the number of carbon atoms in alkyl increases,its defoaming ability to partially alcoholyzed PVA presented a gradual increase initially and then minimized again.The strongest defoaming was observed when the carbon atom in the alkyl reached 8 for n-octyl alcohol.The configuration of alkyl carbon chain played important role in the defoaming ability of monohydric alcohol.The defoaming ability of linear n-octyl alcohol was superior to that of branched ones like iso-and sec-octyl alcohols.As the dosage increases,the defoaming ability of n-octyl alcohol gradually increased,whereas the adhesion of PVA paste to fibers and the mechanical properties of sizing film declined gradually.The increase in the dosage of n-octyl alcohol had no distinctive influence on the desizability of PVA,and the desizing efficiency was greater than 95%,meeting the requirements to desizing of printing and dyeing pretreatment.Based on the defoaming ability,adhesion to fibers,mechanical properties of sizing film,and desizability,the dosage of n-octyl alcohol could be recommended in the range of 0.125%~0.25%.Moreover,organic silicon,three commonly used defoamers,i.e.,sodium stearate,and wax were evaluated in order to meet the actual demand of textile enterprises for eliminating the foam on starch/partially alcoholyzed PVA mixture.The evaluation on the defoamers was accessed in terms of defoaming ability,foam-supression,paste viscosity,adhesion to fibers,surface tension,contact angle,mechanical properties of starch/PVA film,and desizability.The defoaming ability of the defoamers was revealed and the influence of the defoamers on sizing performance of mixture was explored.The investigation results showed these defoamers all showed obvious effect to defoam and supress the foam of starch-PVA mixture.However,they had adverse influences on the adhesion and film properties.It was observed that organic silicon exhibited the strongest ability to defoam and suppress the foam on the paste,followed by wax,and with the weakest for sodium stearate of these three defoamers.Sodium stearate had the lowest negative effect with the strongest adhesion of the mixture to fibers.And wax displayed the highest negative influence on the adhesion.The decreasing amplitude in tensile properties of sizing film was the lowest while sodium stearate exhibited the greatest amplitude in the properties.These three defoamers had no significant influence on the desizing efficiency of starch/partially alcoholyzed PVA since the desizing efficiencies were all more than 95% which met the requirements of printing and dyeing pretreatment.Finally,in order to further improve defoaming ability of the defoamers to be blended with the PVA and reduce the negative effect of defoamers on sizing production,composited defoamer was prepared by blending the n-octyl alcohol with strongest defoaming ability and the organic silicon with best foam-supression ability.Defoaming ability of the defoamer to partially alcoholyzed PVA was explored and the influence of the defoamer upon the end-use ability of partially alcoholyzed PVA was investigated by means of sizing experiments.The experimental results showed the defoaming and foam-supression abilities of the defoamer were better than those of n-octyl alcohol and organic silicon.The JU-B defoamer had prepferable defoaming and foam-supression ability to the foam of partially alcoholyzed PVA with lower adverse influence on the properties of the yarns sized with partially alcoholyzed PVA.Furthermore,the use of the defoamer had no adverse effect on desizing.Therefore,JU-B defoamer showed potential in the practicle application of warp sizing.