STUDY ON STABILITY OF ASA EMULSION FOR SIZING OF PAPER

Abstract

In alkaline papermaking process, use of alkenyl succinic anhydride (ASA) for internal sizing of paper is continuously increasing. ASA imparts sizing to paper quicker than that imparted by alkyl ketene dimer (AKD). Cationic starch (CS) is the conventionally used stabilizer for ASA emulsification. There are two main reasons that restrict the wide spread use of ASA during papermaking, (a) low shelf life of ASA emulsion (b) the sticky conduct of hydrolyzed ASA. The available literature indicates that the shelf life of ASA emulsion can be achieved up to about 4 hours by using different protective colloids. Few references are available of the literature on the effect of different pulp furnishes and fillers on the sizing efficiency of ASA emulsion prepared by using polymers other than CS and the stabilizing effect of different protective colloid is scanty. The objectives of the present study are as follows:  To study the possibility of enhancing the shelf life of ASA emulsion prepared by using different polymers.  Study the effect of ASA emulsions prepared by using different polymers on mixed hardwood, bagasse and recycled pulps along with different fillers. The study has been presented in eight chapters. Introduction was provided in chapter 1 of this thesis in which the factors influencing the quality and stability of ASA emulsion were explained including the concept of internal sizing. The stability mechanism was discussed followed by problem statement and the objectives of this thesis. So, meticulous study was required to examine the impact of different protective colloids on hydrolysis of ASA emulsion at varying ratios of ASA to stabilizer beyond the already reported time period. It was equally essential to study the impact of ASA emulsion prepared by using different protective colloids using different pulp furnishes and fillers. Literature review was included in chapter 2 on the issues with the ASA sizing viz. low shelf life of ASA emulsion and the sticky behavior of hydrolyzed ASA. This chapter provided the overview of main sizing processes reported in literature with their merits & demerits. The various methods for the measurement of sizing degree followed by stabilization and destabilization phenomenon of an emulsion have been discussed at the beginning of this chapter. Different polymers which iv enhance the stability of ASA particles and their interaction with ASA molecules have been mentioned & discussed. Keeping in view the diversity of raw material i.e. pulp furnishes, it further elaborates, the sizing behavior of different pulps and fillers for paper making. Finally national and international status of the work carried out for the enhancement of ASA emulsion stability and the future prospects have been prospected. The thorough understanding and mastery of the underlying stability mechanism of ASA molecules will be premise of the research and applications of highly stable ASA emulsion by the papermakers. The experimental part was discussed in chapter 3 in which the details of raw materials and various commercial & laboratory grade chemicals were mentioned. Various methods followed for the characterization of chemicals, process water and pulps & the methods of ASA emulsification were discussed. Various measurement techniques viz. determination of particle size distribution, infrared spectroscopic analysis, measurement of hydrolysis content of ASA, imaging analysis of ASA emulsions and infrared spectroscopic analysis of handsheets along with details of the instruments used were also mentioned. The methods for the measurement of sizing and physical/ strength properties of handsheets were also discussed at the end of this chapter. The stability mechanism and sizing performance of ASA emulsion stabilized by polyvinylamine (PVAm) macromolecules using different pulps viz. mixed hardwood (MHW), bagasse (BBS), recycled (RCL) and fillers viz. talc, ground calcium carbonate (GCC) & precipitated calcium carbonate (PCC) were discussed in chapter 4. Emulsion stability was achieved even with low dosage of vinylamine polymer as 2.5% of ASA as compared with the required dose of cationic starch at 200% of ASA. Interaction between carbonyl group of ASA and amine group of polyvinylamine was confirmed by FTIR spectra of ASA emulsion prepared by PVAm which might attribute to formation of N-alkyl acid amide by the reaction between carbonyl group of ASA and amine group of PVAm. ASA emulsion stabilized with PVAm was found to be stable at broader range of pH and temperature. Better sizing performance was observed with BBS pulp followed by RCL pulp and MHW pulp. It was evident from the crystallinity ratios (Cr.R.1 and Cr.R.2) and value of H-bond energy that BBS pulp has the maximum amorphous region in the cellulosic fiber that may possibly be translated into lesser chemical requirement to attain the same properties like Cobb60, contact angle followed by v RCL pulp and MHW pulp. Superior sizing was observed with talc filler followed by GCC and PCC filler. The sizing performance of ASA emulsion stabilized by polyacrylamides macromolecules was discussed in chapter 5. The required dose for PAM-2 was about 5% of ASA and that for PAM-1 was about 10% of ASA to form stable emulsions up to 4 hours and 3 hours, respectively since their preparation. Emulsions started losing the stability on further increasing the time period. The greater stabilizing efficiency of PAM-2 was possibly due to its higher molecular weight (1.87x1012) than the molecular weight of PAM-1(6.12x1011). The interaction between PAM and ASA molecules was confirmed by the FTIR spectroscopic analysis. The behavior of PAM stabilized ASA emulsion with different pulps and fillers was found in good agreement with that of PVAm stabilized ASA emulsion. In 6th chapter, poly-DADMAC was used as stabilizer for ASA emulsification at various ratios of ASA to poly-DADMAC. It provided stability to ASA emulsion up to 3 hours even at very low dose of poly-DADMAC (2.5% of ASA). Being a high charge density material it neutralized the cationic charge demand of the paper making stock to a great extent and adversely affected the sheet formation as observed visually. The study was extended to determine the effect of different fillers using MHW pulp on the performance of poly-DADMAC stabilized ASA emulsion but no positive effect was observed for the improvement of sizing properties and formation of handsheets. The effect of different ions present in process water on performance of polyvinylamine based ASA emulsion was discussed in chapter 7. PVAm-2 diluted with de-ionized water produced a stable ASA emulsion while poor emulsification was observed by using the process water for the dilution. So, the fresh water was examined to determine the level of various ions present in it, which restricted the emulsification. This chapter deals with the study on effect of different ions viz. Ca2+, Mg2+, Cl−, SO4 2- & HCO3- present in process water on the performance of ASA emulsion prepared by using PVAm-2 as stabilizer. The concentration of calcium ions was found to be higher and of Mg2+ ions was less than that of maximum permissible limit which may be responsible for the poor emulsification of ASA. It was also observed that chloride ions adversely affected while bicarbonate ions assisted the ASA emulsification. Papermakers can characterize process water before using in ASA emulsification in order to know the level of various ions vi present, as the study has provided the information about the individual effect of various ions present in process water. The 8th chapter included the conclusion of this thesis by including the results, major achievements along with recommendations for future scope in this field. The research objectives mentioned in chapter 1 were effectively achieved by the experimental work. ASA emulsions prepared with both PVAms were found to be stable up to about 4 hours even with low dosage of vinylamine polymer. The PAM- 1 & PAM-2 stabilized ASA emulsions were found to be stable up to 3 hours and 4 hours, respectively. Interaction of PVAms and PAMs were confirmed through FTIR spectroscopic analysis. Poly-DADMAC was not found an efficient stabilizer for application in paper sizing. The study conducted with different furnishes showed better sizing with BBS and RCL pulp than MHW pulp. It was observed from the crystallinity ratios (Cr.R.1 and Cr.R.2) and the energy of H-bonds that BBS pulp has the maximum amorphous region in the cellulosic fiber that might possibly be translated into less chemical requirement to attain the same properties like Cobb60, contact angle followed by RCL pulp and MHW pulp. Superior sizing was observed with talc filler followed by GCC and PCC filler. PVAm diluted with deionized water produced a stable ASA emulsion while poor emulsification was observed by using the process water for the dilution of PVAm. The concentration of calcium ions was higher in process water than the maximum permissible limit which may be responsible for the poor emulsification of ASA. It was also observed that chloride ions adversely affected while bicarbonate ions assisted the ASA emulsification. Future research efforts should be made to develop the protocol to use the process water for the preparation of ASA emulsion utilizing various polymers as studied above for commercial applications and papermakers can characterize process water before using in ASA emulsification in order to know the level of various ions present, as the study has provided the information about the individual effect of various ions present in process water. The study further opens up the research scope to enhance the stability of ASA emulsion by using various other stabilizers or blends of various stabilizers so that the emulsion can be transported as ready to use emulsion to eliminate the in situ emulsification of ASA and to find out others mechanisms of various pulps for the varying chemical dose requirement to get the same sizing properties.