FINISHING AGENT

Abstract: The use of amylopectin-type starch obtained from potato that has been subjected to a genetical engineering modification to suppress the formation of amylose-type starch, as a finishing agent in papermaking is described.

Description: FINISHING AGENT The present invention relates to the use of amylo¬ pectin-type starch or derivatives thereof as a finishing agent in papermaking. More specifically, the present invention relates to the use of amylopectin-type starch obtained from potato that has been modified by genetical engineering, to sup¬ press the formation of amylose-type starch. Background of the Invention In the manufacture of paper and paperboard intended for some kind of printing the print-receiving surface is treated either by a pure starch solution or by a coating slip. When traditional starch of any known origin (potato, maize, wheat and tapioca) is used, more than one chemical modification step is required in many cases to obtain a product possessing sufficient stability. The various modification steps usually include a stabilising step, for instance an etherification reaction with propene dioxide or an esterification reaction with vinyl acetate or acetic anhydride, and a degradation step, such as oxidation, en- zymatic degradation, acid hydrolysis or so-called ther o- chemical conversion. During the above steps substitution of the starch takes place, and the degree of substitution pertaining to the corresponding stabilising step usually amounts to 0.01 - 0.5 mole/mole glucose, preferably 0.05 - 0.20 mole/mole. The necessity to carry out more than one modifica¬ tion step entails costs and has negative effects on the environment, and a reduction of the required number of chemical modification steps thus is desirable. Object of the Invention The object of the present invention is to reduce the number of chemical modification steps necessary to obtain a stable finishing agent for use on paper. This object is achieved by using amylopectin-type starch of the kind out- lined in the introduction, which starch additionally pos¬ sesses the characteristics defined in the appended claims. Summary of the Invention In accordance with the present invention amylo- pectin-type starch or derivatives thereof thus are used as a finishing agent in papermaking. The expression "amylopectin-type starch" as used throughout in the present application text relates to starch obtained from potato that has been submitted to genetical engineering in order to suppress the formation of amylose-type of starch. The expression "derivatives thereof" relates to chemically, physically and/or enzy¬ matically derivatised amylopectin-type starch. The amy¬ lopectin content of amylopectin-type starch is in excess of 95%, preferably in excess of 98%. The remaining ingre¬ dient in amylopectin-type starch is amylose. A detailed description of the above amylopectin-type starch and derivatives thereof and the methods of their production is found in the Swedish Patent Specification 9004096-5 (Amylogene HB) . When practising the invention, amylopectin-type starch is added in amounts of 0.5-8% by weight, prefer¬ ably 2-6% by weight, during the production process. By means of the present invention it thus becomes possible to eliminate the above-mentioned stabilising step, since the amylopectin in the starch used in accord¬ ance with the invention, having strongly reduced amylose contents on account of its branched structure, possesses excellent stability. Thus, only one chemical reaction is required to produce the finishing agent, and consequently surface-sizing and coating products may be manufactured in a manner that is considerably less harmful to the environment than has hitherto been possible. The reason therefor is not only the elimination of the modification step but also that it has become possible to alter the degradation step. In consequence of this alteration the amount of oxidising agent required to degrade the amylo- pectin in the starch used in accordance with the inven¬ tion is approximately 50% lower than the amount required to degrade traditional potato starch. In general, sodium hypochlorite, hydroperoxide or some type of persulphate compound, such as sodium persulphate, is used as the degradation chemical. It is not previously known to use amylopectin-type starch as a finishing agent for use on paper. Practical tests have shown, however, that the use of amylopectin- type starch gives surprising and unexpected combined effects inasmuch as it permits the finishing agent to be produced by a simplified as well as environmentally less harmful method. The invention will be explained in greater detail in the following by means of the Examples below. Example 1 Oxidised starch based on potato starch was produced in the following manner. 100 kg potato starch were formed into a slurry in water. The pH-value of the slurry was adjusted to 9.5 by means of sodium hydroxide. 23.4 litres of sodium hypochlorite containing an active substance of 150 g/litre active chlorine were added. The pH-value of the reaction was maintained constant by addition of sodium hydroxide. Once the reaction was complete, i.e. when all chlorine had been used up, the reaction was interrupted by neutralisation, by means of hydrochloric acid, to a pH-value of 5.5, whereupon the product was de¬ watered and washed before drying. The following values were obtained from an analysis of the product: Dry contents, % 82 . 4 pH of slurry 8 . 0 pH of solution 6 . 4 Conductivity, μS/cm 155 Contents of carboxyl, 0 . 87 Viscosity at different tempera attuurreess Viscosity, cP, 25%, 100 rpm 8 800°°CC 80 70 ° C 95 50°C 135 30°C 232 Viscosity at different concentrations Viscosity, cP, 50°C, 100 rpm 10% 26 15% 47 20% 76 25% 135 30% 343 35% 600 Stability Viscosity, cP, 25%, 25°C, 100 rpm 0 min 350 60 min 580 120 min 780 180 min 1250 1 day firm gel formed At comparatively high concentration levels (25%) , the product exhibits very poor stability at low tempera¬ tures (25°C), and already after the lapse of two h the viscosity is more than doubled. This behaviour is typical in traditional oxidised starches, and these products can only be used at low concentration levels and when the temperature is at least 50°C. Example 2 Oxidised amylopectin starch from potato was produced in the following manner. 100 kg amylopectin-type starch was formed into an aqueous slurry. The pH value of the slurry was adjusted to 9.5 by means of sodium hydroxide. 11.0 litres of sodium hypochlorite containing an active substance of 150 g/litre active chlorine was added. The pH value of the reaction was maintained constant by addition of sodium hydroxide. Once the reaction was completed, i.e. when all chlorine had been consumed, the reaction was interrupted by neutralisation, by means of hydrochloric acid, to a pH value of 5.5, whereupon the product was dewatered and washed before drying. The following values were obtained in an analysis of the product: Dry contents, % 83.5 pH of slurry 8.0 pH of solution 6.1 Conductivity, μS/cm 149 Contents of carboxyl, % 0.76 Viscosity at different temperatures Viscosity, cP, 25%, 100 rpm 80°C 78 70°C 92 50°C 131 30°C 198 Viscosity at different concentrations Viscosity, cP, 50°C, 100 rpm 10% 24 15% 44 20% 73 25% 116 30% 203 35% 603 Stability Viscosity, cP, 25%, 25°C, 100 rpm 0 min 267 60 min 267 120 min 267 180 min 270 1 day 311 2 days 315 3 days 350 The stability of the product is highly satisfactory, also at low temperatures (25°C), and the viscosity had increased only marginally after storage of the product for up to 3 days. The product may be used without diffi¬ culty in high concentrations, also if the temperature is allowed to become lower. This is possible in the case of products having potato starch as its base only if the product is stabilised by an esterification or etherifica¬ tion reaction.

Claims: CLAIMS 1. The use of amylopectin-type starch obtained from potato that has been modified by genetical engineering to suppress the formation of amylose-type starch, as a fin¬ ishing agent in papermaking. 2. The use in accordance with claim 1, wherein the amylopectin-type starch contains more than 95% amylopec- tin, preferably more than 98% amylopectin. 3. The use in accordance with claim 1, wherein a derivative of chemically, physically and/or enzymatically derivatised amylopectin-type starch is added as a finish¬ ing agent. 4. The use according to any one of the preceding claims, wherein the amylopectin-type starch or deriva¬ tives thereof is added in amounts of 0.5-8% by weight, preferably 2-6% by weight. 5. The use according to any one of the preceding claims, wherein the amylopectin-type starch is subjected to oxidation, enzymatic treatment, acid hydrolysis or thermo-chemical conversion. 6. The use as claimed in claim 5, wherein the thermo-chemical conversion is effected by means of com- pounds of persulphate or peroxide.

Inventors: WIKSTROEM OLLE, WIKSTROEM, OLLE
Applicants: SVERIGES STAERKELSEPRODUCENTER, WIKSTROEM OLLE, SVERIGES STAERKELSEPRODUCENTER, FOERENING UPA, WIKSTROEM, OLLE
Application year: 1996
Main classification: D21H17
IPC codes: C08B35, D21H17, D21H19