Structures of Alkenyl Succinic Anhydride (ASA) Components in ASA-Sized Papersheet *

180 SＥN'IGAKKAISHI(報文) (45) Transaction (Received August 28, 1995) Structures of Alkenyl Succinic Anhydride (ASA) Components in ASA-Sized Papersheet * MasakiNishiyama, Akira Isogai, and FumihikoOnabe Facultyof Agriculture,The University of Tokyo, Bunkyo-ku, Tokyo, 113 Japan Abstract:Alkenyl succinic anhydride (ASA) is oneof the reactivesizes used as cationicemulsions at wet-endof papermakingprocess. In orderto makeclear the mechanism ofASA sizing, structures of ASAcomponents retained in handsheetswere studied using model compounds and analyticaltechniques. The results of modelexperiments usinglow-molecular-weight cellulose and cationicstarch showed that ASAwas predominantly hydrolyzed to alkenylsuccinic acid (ASAcid) in the presenceof waterwithout forming ester linkageswith hydroxyl groups of carbohydrates.Sheet-form and fibrous-formextractions with organic solvents under various conditions indicated that mostof ASAcomponents were present as the structureof ASAcidin ASA-sizedhandsheets. The results of curingtreatments of ASA-sized handsheets and impregnationtreatments of ASA-relatedcompounds into filter pa- persalso were negative to the formationof esterlinkages between ASA and cellulose-OH.Cellulase-treatments of ASA-sizedhandsheets followed by IRanalysis of the obtainedresidues showed that ASAcomponents were mostly presentas thestructure of ASAcid in papersheet.ASAcid aluminum salts may be present to someextent in paper- sheetprepared by ASA-alumsystems. All these results imply that appearanceof sizingfeatures for ASA-sized papersheetis broughtabout by ASAcidmolecules in papersheet.However, since non-reactive ASAcid has no siz- ingeffect when added to pulpsuspension, the reactivestructure of ASAmust be necessaryfor papersizing be- causeof some mechanisms other than the formation of esterlinkages with hydroxyl groups of pulp fibers. 1. Introduction preparation (1). The amounts of ASA required for sufficient sizing degrees of papersheet in the practical inter- Alkenyl succinic anhydride (ASA) is one of the typical nal sizing process are 0.1-0.2% on dry weight of pulp or neutral sizes as well as alkyl ketene dimer (AKD) for lower. paper, giving water-repellency to paper efficiently by Since ASA has the structure of reactive acid anhy- being added as cationic emulsions to pulp suspension dride, the ester formation between ASA and hydroxyl even at 7-9 of pH due to the presence of calcium carbon- groups of cellulose surfaces of pulp fibers in ASA-sized ate used as a filler. ASA is synthesized from internal ole- papersheet has been believed to bring about the highly fin hydrocarbons (average carbon numbers = 18), origi- efficient sizing effects (Fig. 1). Primary reasons for sup- nating from oil, and maleic anhydride by the ene-addition porting this ester-linkage formation are; 1) reactive reaction. Commercially available ASA generally contains structure of ASA is necessary for paper-sizing as in the polyethylene glycol (PEG) to some extent, and is emulsi- case of AKD, and 2) even after Soxhlet extractions of fied with aqueous cationic starch solutions in each paper ASA-sized papersheets with chloroform, ASA compo- mill just before using as a wet-end additive. Since ASA nents remained partly in the sheets and they had still in the emulsion is easily hydrolyzed to alkenyl succinic sufficient sizing features (2-4). However, since ASA con- acid (ASAcid), which has nearly no sizing effect, the ASA tent in papersheet is so low (generally lower than 2 emulsion has to be used within 30 min after the emulsion mg/g) that the structure of ASA components retained in papersheet could not be analyzed by the usual methods, 'This article i s a Part 1 of serial study's: Mechanism of and thus the mechanism of paper sizing with ASA has Paper Sizing with ASA. not been established yet. (46) Vol.52,No. 40996) 181 (alum) are added as wet-end additives to pulp suspension in ASA-sizing, and therefore ester linkages between ASA and PAE, and/or ASAcid aluminum salt may be present in the ASA-sized papersheet as shown in Fig. 1. Hence, the efficient sizing of papersheet with reactive ASA may not be explained by the simple mechanism of the ester formations between ASA and cellulose-OH. In this paper, therefore, structures of ASA components in ASA-sized papersheet are studied, using analytical techniques similar to the AKD studies reported previous- ly (7). Especially, the possibility for ASA to form ester linkages with cellulose-OH in ASA-sized papersheet was examined. 2. Experimental 2.1 Materials Commercial hardwood bleached kraft pulp (HBKP) beaten to 450 mL of Canadian Standard Freeness was used for handsheet-making. An ASA sample (containing Fig.1 Possible reactions of ASA with cellulose, water, PAE and alum in papersheet. about 5% PEG), 2-hydroxyprpyl-3-trimethylammonoyl starch Cl salt (HPTMA-starch) with degree of substitu- Generally a strong catalyst such as sulfuric acid, tion (DS) of 0.03, and PAE (WS-570, Japan PMC Co.) methanesulfonic acid or triethylamine is necessary for were commercial products. Low-molecular-weight cellu- esterifications of cellulose with acid anhydrides, and lose with degree of polymerization (DP) of 7, which is sometimes non-aqueous media were used for the ester- soluble in DMSO, was prepared from Whatman CF1 ifications (4-6). However. ASA-sized handsheets have according to the reported method (8). Other chemicals sufficient sizing degrees even after drying the wet paper and solvents used were of pure grade. web at 20°C without curing treatments. Furthermore, ASA emulsion containing 0.5% ASA and 1% HPTMA- since water is always present in the papermaking pro- starch was prepared by using a double-cylinder type cess, it is not plausible that the ester formation proceeds homogenizer, and was used within 30 min after the emul- predominantly in papersheet rather than the reaction be- sion preparation for usual handsheet-making. An ASA tween ASA and water (or hydroxyl ion). Especially, emulsion, in which all ASA molecules were hydrolyzed to under alkaline papermaking conditions, where calcium ASAcid by being left standing for 3 days at room carbonate is present, the reaction between ASA and OH temperature, was used as an "old ASA emulsion" sample. seems to occur predominantly rather than the solid-phase Complete hydrolysis from ASA to ASAcid in the "old reactions between ASA and cellulose-OH. Since Soxhlet ASA emulsion" was confirmed from the IR spectrum of extractions of papersheet with chloroform, which has its freeze-dried material. nearly no swelling effect on cellulose, can not extract Handsheets with basis weight of 60 g/m2 were pre- even physically-trapped organic compounds completely pared according to TAPPI Test Method (9). In general from cellulosic fibers, extractions of papersheet must be procedure, the ASA emulsion, PAE and alum were added carried out in swollen fibrous form with aqueous organic in this order to the 0.15% pulp suspension. Some hand- solvents (7). sheets were prepared without alum and/or PAE. The Furthermore, ASA components may form other struc- pHs of the pulp suspensions were about 6.5 and 6.9 for tures than the esters and/or ASAcid in papersheet . the systems with and without the 1% alum (on dry Generally, polyamideamine-epichlorohydrin resin (PAE) weight of pulp) addition, respectively. The pressed wet or other cationic polymers as well as aluminum sulfate handsheets were dried at 20 °C and 65% relative humid- 182 SEN'I GAKKAISHI(報文) (47) ity (R.H.) for more than one day. A part of the hand- grated with a double-cylinder type homogenizer for 10 sheets thus prepared were cured at 105 °C for 30 min, min. Fresh 240 mL acetone was added to the suspension, and then they were conditioned at 20 °C and 65% R.H. and it was stirred at 70 °C for 12 h. An acetone solution ASAcid was prepared from ASA by refluxing with containing 1 mg of tetradecanoic acid used as an internal aqueous acetone (water : acetone = I : 1) for 3 h, and standard for gas-chromatography was added to the sus- ASAcid monomethyl ester was prepared from ASA by pension, and its pH was adjusted to 1-2. The suspension refluxing with dry methanol for 3 h. The structures of was filtered and the residual fibers were washed thor, these ASA-related compounds containing a small amount oughly with fresh acetone. The filtrate and washings of PEG were confirmed by 'H- and 13C-NMR, and IR were combined, and the mixture was concentrated to ab- spectroscopy. out 30 ml, by evaporation. Then the.oily aqueous solu- 2.2 Model Experiments tion was extracted three times with chloroform, The The low-DP-cellulose, ASA and water (1 : 1 : 1, by chloroform-soluble fractions were combined, and the ex- weight) were sufficiently mixed on a metal plate, and the tracted material was dried by evaporation followed by mixture was dried at 20-105 °C for 30-120 min. Then, drying in vacuo. A fresh diazomethane-diethyl ether solu- the mixture was extracted with acetone at 80 °C for 12 tion was added to the sample, and then the mixture was h. The acetone-soluble fraction and the acetone-insoluble stored at room temperature for one day for complete residue were dissolved in chloroform-d, and DMSO-de, methylation of carboxyl groups of ASA components and respectively, for their NMR analysis. The low-DP-cellu- the internal standard. The methylated sample was sub- lose (0.1 g) was suspended in dioxane (50 mL) containing jected to gas-chromatography for determining ASA com- ASA (0.1 g), and this suspension was heated at 80 °C for ponents extracted under neutral and alkaline conditions. 4 h. The residue was collected by filtration and washing 2.5 Impregnation of ASA and its Related Compounds thoroughly with acetone. The ASA emulsion containing into Filter Paper 0.5% ASA, 1% HPTMA-starch and 98.5% water was One % acetone solutions (wt./vol.) of ASA and its re- spread on a metal plate, and was dried at 105 °C for 30 lated compounds shown in Table 3 were prepared, and a min.

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