EP2148003A1

EP2148003A1 - Process for the production of a modified starch containing product, modified starch containing product obtainable by that process and use thereof in paper manufacture

Info

Publication number: EP2148003A1
Application number: EP08160881A
Authority: EP
Inventors: Thomas BRÜMMER; Johannes Felix Hintermayer; Jochen Hoffmann; Oliver Struck
Original assignee: Muehle Rueningen & Co KG GmbH
Current assignee: MUEHLE RUENINGEN GMBH & CO. KG; Nouryon Chemicals International BV
Priority date: 2008-07-22
Filing date: 2008-07-22
Publication date: 2010-01-27

Abstract

The present invention is directed to a process for modifying a starch containing product with at least one polyaminoamide epihalohydrine resin and modified starch containing product obtainable by said process and its use as dry strength agent in paper manufacture.

Description

The present invention relates to a process for the production of a modified starch containing product, the modified starch containing product obtainable by said process as well as the use thereof in paper manufacture. In particular, the modified starch containing product is useful in the production of a paper of high strength (and recycling properties).
There are known a plurality of additives for adjusting the properties of paper depending on the desired application of the paper obtained. For example, there are known additives for enhancing the strength of the paper in the dry state as well as in the wet state.
Currently, a particular aspect in paper manufacture is the recyclability of the paper as well as the suitability of the paper for the production of recycled paper in a quality as high as possible. For sufficient recyclability the wet strength of the paper should be not too high. On the other side the paper should have good performance characteristics, in particular sufficient dry strength.
In view of sustainability and environmental protection it is desirable to use additives based on renewable raw materials.
For example, it is common to add starch to the paper pulp for enhancing the dry strength. Since the absorption capacity of paper fibers for starch is only low, the resulting improvement of dry strength is only insufficient. Further, starch has to be isolated from its natural source such as vegetable flour thereby increasing the necessary expenditures.
In US Patent Application Publ. No. 2005/0109476 an agent for increasing the absorption capacity of paper pulp for starch is disclosed wherein said agent is obtained by co-extrusion of the starch with a polymer with vinylamine units.
In place of starch or in addition to starch cereal flour can be used directly. Though this agent helps to increase the dry strength of paper further improvement is desirable.
In US Patent 6,616,807 B1 the use of cationic starch as dry strength agent in paper manufacture is disclosed. The cationic starch is obtained by reacting the starch with an amine containing polymer, for example a water-soluble polyaminoamide cross-linked with epichlorohydrin, by heating an aqueous solution containing 0.1 to 10 parts by weight starch and 0.5 to 10 parts by weights per 100 parts by weights of starch of polymer above the gelatinization temperature of the starch with stirring and under pressure. The aqueous mixture obtained is, after cooling, added directly to the paper stock.
US Patent 6160050 discloses starch modified with a cationic polymer intended to be used in paper making.
Generally, in the prior art it is disclosed that the reaction of the starch and the polymer takes place at the paper mill, typically at a low dry content in a jet cooker or similar starch cooking device, prior to addition to the paper making process.
US Patent 3962159 discloses graft co-polymers prepared by condensing a polyamideamine substrate with starch in the presence of a condensing reagent such as epichlorohydrin. The resulting product is intended to be used in paper making.
In view of the above the present invention relates to a process for the production of a modified starch containing product and the modified starch containing product obtainable by that process, wherein said starch containing product is useful as an agent for the paper manufacture for obtaining paper with good performance characteristics.
In particular, it is an object of the present invention to provide a modified starch containing product which is useful in enhancing the dry strength of paper.
It is a further object of the present invention to provide a ready-made solid product which can be stored and metered to the paper stock on need.
It is a further object of the invention to provide a paper and process for manufacturing thereof which are advantageous with respect to environmental aspects, in particular in view of amount of waste generated on dewatering the paper pulp. To this respect a process is desirable if the dry strength agent is retained within the fibers of the paper web with as small amount as possible of the agent being discharged into the paper mill effluent.
It is still a further object of the invention to provide a paper obtained by the use of the present modified starch containing product which is easily repulpable and usable in the paper recycling process.
According to the present invention these objects can be achieved by a process for the production of a modified starch containing product comprising subjecting a starch containing product and a polyamidoamine epihalohydrin resin (PAAE) to gelatinizing conditions at a dry content of at least 50 weight%, optionally further comprising comminuting the resulting mixture.
Further, the invention relates to a modified starch containing product obtainable by said process.
Moreover, the invention relates to the use of the modified starch containing product in paper making, in particular as a dry strength agent in paper making.
A further aspect of the invention relates to a process for the production of paper comprising adding a modified starch containing product of the invention to a stock containing cellulosic fibers and dewatering the stock to obtain paper.
Still a further aspect the invention relates to a paper obtainable by the use of the modified starch containing product of the present invention.
The starting material used according to the invention can be any starch containing product, including starch as such, a starch containing flour or any combination thereof. The starch can be a native, cationic, anionic, amphoteric starch or any kind of modified starch. The starch can be isolated from a common vegetable starch source such as flour. Any vegetable flour can be used, cereal flours being, however, preferred.
A great advantage of the present invention is that flour can be used directly without the need for isolating the starch therefrom.
Examples of useful starch containing products are wheat, spelt, oat, barley, sorghum, corn, rice, rye, potatoes, tapioca and pea, particularly flour of one or more thereof, or starch obtained therefrom and any combination thereof.
Cereal flours contain a high proportion of starch, with possible variation in the proportion and composition of the starch depending on the cereal type.
Particularly preferred starch containing products are rye flour or wheat flour as well as a flour having a proportion of starch and preferably composition of the starch corresponding to or being similar to that of rye flour or wheat flour. The flour used as starch containing product can be a commercially available flour.
The flour can be used in combination with starch as such, which can be advantageous if a higher proportion of starch is desired, for example, in case of a flour containing a relatively low starch proportion. Also mixtures of different flours and/or starches can be used.
According to the invention the starch containing product is modified with at least one polyamidoamine epihalohydrin resin (hereinafter referred to as PAAE), preferably polyamidoamine epichlorohydrin.
Polyamidoamine-epihalohydrin resins include those that have been prepared with epihalohydrin, e.g. epichlorohydrin, as a reactant, either during the polymerisation or in the modification of an existing polymer. Such resins are widely used as wet strength agents in paper making and are commercially available, e.g. under the trademarks Eka WS 320, Eka WS 320 RC, Eka WS XO.
Further, preparation of polyamidoamine epihalohydrin is disclosed in the literature, e.g. in any one of US 4450045 , US 3311594 , US 4336835 , US 3891589 , US 2926154 , US4857586 , US4975499 , US5017642 , US 5019606 , US 5093470 and US 5516885 .
The polyamidoamine epihalohydrin resin is preferably in an aqueous solution that optionally further may comprise a water-miscible solvent such as methanol, ethanol or dimethyl formamide. The molecular weight can vary within wide ranges and M_w may, for example, be from about 50000 to about 1000000 or higher.
The polyamidoamine epihalohydrin may also be a product with high solids content such as those disclosed in EP Application No. 08159404.6 .
Epihalohydrins that can be used include epibromohydrin and epichlorohydrin, preferably epichlorohydrin. Suitably, the polymers are produced using from about 0.5 to about 2 moles of epihalohydrin per mole of basic nitrogen in the polyamidoamine.
The polyamidoamine is preferably a reaction product of a polycarboxylic acid or a derivative thereof, suitably a dicarboxylic acid or derivative thereof, and a polyamine. Derivatives of carboxylic acids include e.g. anhydrides, esters and half esters. Suitable poly-carboxylic acids include saturated or unsaturated aliphatic or aromatic dicarboxylic acids. Preferably, the polycarboxylic acids contain less than 10 carbon atoms.
Preferred polycarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid and derivatives and mixtures thereof, of which adipic acid is particularly preferred.
Preferred polyamines include polyalkylene polyamines, or mixtures thereof, having the following formula:

H₂N-(CR¹H)_a-(CR²H)_b-N(R³)-(CR⁴H)_c-(CR⁵H)_d-NH₂ (I)

in which R¹-R⁵ represent hydrogen or lower alkyl, preferably up to C₃ and a-d represent integers of from 0 to 4. Preferred polyalkylene polyamines include diethylene triamine, tri-ethylene tetraamine, tetraethylene pentaamine, dipropylene triamine, and mixtures thereof.
The polyamines of formula (I) can be combined with other polyamines or mixtures of other amines. Preferably, these amines have any of the following formulae II-VII:

R⁷R⁸N-(-(CH₂)_g-CR⁹H-(CH₂)_hN(R¹⁰)-)_i-H (III)

HR¹¹N-(CH₂)_j-CR¹²H-(CH₂)_k-OH (IV)

HNR¹³R¹⁴ (V)

H₂N-(CH₂)_l-COOH (VI)

in which R⁶-R¹⁴ represent hydrogen or lower alkyl, preferably up to C₃, e-I represent integers of from 0 to 4, and m represents an integer of from 0 to 5.
The polycarboxylic acid and the polyamine may, for example, be applied in a molar ratio from about 1:0.5 to about 1:1.5.
In the art polyamidoamine may also be referred to as polyaminopolyamide, polyamidopolyamine, polyamidepolyamine, basic polyamide, cationic polyamide, aminopolyamide, amidopolyamine or polyaminamide.
A polyaminoamide epihalohydrin resin suitable for the present invention and processes for the production thereof are disclosed in European Patent EP 0589 917 B1 which is incorporated herein by reference.
For the present invention a single PAAE or a combination of two or more types thereof can be used.
It is assumed that by the modification of the starch containing product with PAAE the adhesion or absorption of the starch containing compound to the paper fibers is improved, the PAAE thus being effective as a kind of fixative.
The amount of PAAE used for the present modified starch containing product is preferably from 1 to 20 weight%, most preferably from 1.5 to 10 weight% and particularly from 2 to 5 weight%, based on the starch containing product with its natural water content.
Gelatinization of starch and flour on heating is a well-known phenomenon. The temperature and time required for gelatinization depends on the type of starch and flour, respectively.
For the present process a starch containing product and PAAE are preferably heated to a temperature sufficient for gelatinization at a dry content of at least 50% by weight, preferably during continuous mixing. The temperature is preferably from 90°C to about 200°C, most preferably from 120°C to 180°C, or from 140°C to 170°C.
It is preferred that mixing takes place under sufficient action of forces, e. g. shearing forces, onto the components.
A measure of the forces acting on the components when being mixed; for example by kneading, stirring etc., is the specific mechanical energy (SME).
The higher the specific mechanical energy input the higher the forces to which the mixture is subjected.
According to the invention the specific mechanical energy input is preferably from 30 to 200 Wh/kg, most preferably from 60 to 120 Wh/kg (Watt •hour per kg reaction mixture).
By subjecting the components to the specific mechanical energy input gives very intensive mixing and, thus, homogenous distribution of the components over the whole mixture can be obtained which is assumed to result in a uniform modification of the starch containing product with PAAE.
During the gelatinization the mixture of starch containing product and PAAE has a dry weight content of at least 50% by weight, preferably at least 60% by weight and most preferably at least 70% by weight.
A dry weight content of at least 50 % by weight means that in the reaction mixture the amount of solvent, usually water, is 50 % by weight or less. Preferably the amount of solvent based on the mixture of starch containing compound and of PAAE is generally within a range of 8 wt % to 40 wt %, preferably 10 wt % to 30 wt % and particularly preferred of from 15 wt% to about 25 wt% (inclusive the natural water content of the components).
If the dry weight content is less than 50 weight percent the effect of the energy input onto the components is reduced. It is assumed that the water content present during the modification of the starch containing product with PAAE affects the properties of the resulting modified starch containing product.
The water content influences the gelatinization and viscosity of the starch containing product, which, in turn, influences the energy input by mechanical shearing and thereby also properties of the resulting product such as molecular weight distribution.. Consequently, even if the water content of the resulting product is subsequently adjusted, for example by drying or wetting, respectively, the respective properties such as molecular weight distribution can be no longer be changed.
Furthermore, a low water content facilitates the further processing of the obtained mixing product to a solid granular end product.
For mixing, in principle, any mixing device can be used which is capable to introduce the necessary specific mechanical energy into the reaction mixture.
Examples include extruders or kneading machines suitable for mixing mixtures of high viscosity. Most preferably an extruder is used. It has been shown that by the action of an extruder reaction mixtures according to the invention with high dry content can be advantageously processed to the desired modified starch containing product.
The preferred time period for the mixing depends on the type of mixing device and is usually from about 5 to 120 seconds, preferably from 30 to 60 seconds. This time period usually corresponds to the time the starch containing product and PAAE are subjected to gelatinization conditions and thus also for the modification.
Use of an extruder as mixing means is particularly advantageous in view of the desired high specific mechanical energy input and the resulting high forces, in particular shearing forces, which can be acted on the reaction mixture.
One extruder which is suitable for the extrusion is a co-rotating twin-screw extruder. An example of a suitable twin-screw extruder is an extruder such as that marketed by the company Bühler under the product designation BCTA.
Further examples of suitable extruders are the BCTH and DNDG, all also purchased by Bühler.
The extrusion preferably takes place at a temperature of 90 to 200°C, especially of 140 to 170°C.
The extrusion preferably takes place during addition of water. The water may be added in the liquid state or at least partially as vapour, for example via a pre-conditioner.
The residence time of the reaction mixture within the extruder is usually from about 10 to 120 seconds, especially 15 to 60 seconds.
The extruder may be coupled to a pre-conditioner.
Pre-conditioning can take place at a temperature of up to 100°C.
Usually, mixing is carried out at a pH-value of from 3 to 8, preferably 5 to 7.
According to need the pH-value can be adjusted by adding base or acid to the reaction mixture.
There is no particular restriction as to the base or acid to be added. Usually a conventional mineral base or acid such as sodium hydroxide and sulfuric acid, respectively, can be used. Also useful are mono- and polycarboxylic acids such as formic acid, acetic acid, adipic acid or citric acid.
The resulting modified starch containing product can be further processed in a manner known in the art to a final product desired for application. For example, it can be comminuted to form a powdery product of suitable particle size. For example it may be milled to form a granulate. The particle size is not critical, although it for good dispersability for paper manufacturing preferably does not exceed 1 mm. Preferably the comminuted product comprises at least 95% (by weight) of particles with a particle size not exceeding 355 µm (on sieving with a 355 µm sieve).
If desired, the resulting modified starch containing product as well as the comminuted or granulated product can be dried. Drying is accomplished by simple cooling of the hot reaction mixture at room temperature and/or by drying in a conventional dryer, for example at about 120°C.
The modified starch containing product of the invention preferably has a dry content of at least 80 weight percent, especially at least 88 weight percent and particularly, preferred at least 92 weight percent, based on the content of starch containing product and polyaminoamide epihalohydrine resin, with the residual being solvent, usually water.
Water that may be present in the modified starch containing product of the invention either originates from the natural water content in the starting product (e.g. flour or starch as such) and/or has been added in the course of the manufacturing process and not being removed during optional subsequent drying.
Optionally the modified starch containing product of the invention may contain additives which may be desirable for paper manufacture.
Said additives can be added during mixing and/or subsequent to mixing to the resulting reaction mixture.
The modified starch containing product of the present invention, in particular in granular form, is useful as ready-made product and can be stored and easily metered to the paper making stock on demand.
Further, since it can be prepared and shipped as a commodity to the paper mill the entire process is simplified compared to carrying out the reaction at the paper mill.
The exact chemical structure of the modified starch is not fully known, but it has been found that the properties are different compared to starch that have been modified with PAAE by other methods, such as in an aqueous suspension of low dry content.
For paper manufacture, the modified starch containing product of the present invention, is added to the paper making stock in a quantity sufficient to adjust the starch content of the resulting paper to the desired value.
It has been shown that the modified starch containing product of the present invention has an excellent absorption to the paper-fibers yielding a paper web which has sufficient starch content required for adequate dry strength.
Due to this good retention only a small amount of the modified starch containing product of the invention is found in the white water, the residual water obtained on dewatering the paper pulp, which means more efficient use of valuable raw materials as well as environmental advantages.
The starch containing product of the present invention can be advantageously added to the paper making stock at the wet end of the paper manufacturing process.
For optimum performance the starch containing product of present invention is preferably dispersed in water and the resulting dispersion metered into the papermaking stock.
Usually, the modified starch containing product can be added to the papermaking stock in a quantity of from about 0.5 wt % (as dry) to about 4 wt % (as dry), preferably from 2.5 wt % (as dry) to 3.5 wt % (as dry) per ton final paper.
In the following the present invention is further illustrated by reference to examples.

Preparation examples 1 to 5

Preparation of modified starch containing product according to the present invention.
In all examples 1 to 5 commercially available wheat flour of type 550 was modified with PAAE.
For examples 1, 2 and 5 as PAAE component Eka WS 320 and for examples 3 and 4 Eka WS 320 RC, each of Eka Chemicals AB were used.
For examples 1 to 4 a Bühler DNDG 62 mm extruder and for example 5 a Bühler BCTH 125 mm extruder was used.
In the modified starch containing products of examples 1 to 5 the water content was in the range of from 5 wt% to 12 wt%, wherein, if necessary, the product obtained by extrusion was subjected to a conventional drying process.
The experimental conditions are shown in table 1.

Reference example 1

Preparation of rye flour modified with polyvinylamine in accordance to US 2005/0109476
For the modification extruder BCTH 125 mm provided with a pre-conditioner BCTC of Bühler was used. The experimental conditions are shown in Table 1.

Table 1:

Ex. No.	1	2	3	4	Ref 1	5
revolution speed of screws [rpm]	50	100	50	100	280	600
torque [%]	53	41	61	49	94	48
pressure before die [bar]	68	40	80	50	38	51
temperature of product before die [°C]	127	151	121	150	162	170
flour [kg/h]	150	150	150	150	1000	1000
polymer [wt %]	5	5	5	5	2	3
water in pre-conditioner [kg/h]					110	90
SME [Wh/kg]	84	130	98	158	100	98
water content reaction mixture [wt%]	28	28	27	27	31	32

Reference example 2

Preparation of a starch compound modified with PAAE in accordance to US 6616807 (cf page 9, lines 5 to 14).
Native maize starch (C*size RG 03719, Cargil Deutschland GmbH) was suspended at 3 % solids in water and mixed with a polyamidoamine epichlorohydrine resin (Eka WS 320, Eka Chemicals AB) in an amount of 3 % dry polymer on starch.
The mixture was heated under vigorous stirring to 90° C and kept at this temperature for 30 minutes.
A slightly turbid solution was obtained, which was further diluted for continous addition to the paper machine.

Example 6

Use as paper additive

The example is to demonstrate the superior performance of the invention as dry strength agent for paper in comparison to polyvinylamine modified starch compounds of EP 1 384 811 A1 (Reference Example 1)
Papers of 110 g/m² were prepared on a pilot paper machine (speed 2 m/min) from a mixed waste furnish provided by a liner & fluting mill. Ash content was 13 %, and the sheet forming conditions at the headbox were conductivity 4000 µS/cm, zeta potential -5 to -6 mV, pH 6.3 - 6.7 and temperature 40 °C. A microparticle system (Compozil®, Eka Chemicals AB), consisting of a cationic polyacrylamide (Eka PL 1510, Eka Chemicals AB) and an anionic silica sol (Eka NP 320, Eka Chemicals AB) was used as retention and dewatering aid.
The modified starch containing products of examples 1 to 4 and Reference Example 1 were dissolved in water at 5 % solids and 50 °C by means of laboratory dispersing unit (Super Dispax SD 40, Ika). The resulting dispersions were further diluted and fed into the papermaking stock at the outlet of the machine chest.
The paper on reel had a moisture content of 3 - 4 %. Sheets were stored for at least 24 hrs at 23 °C / 50 % r.h. before testing. Tensile strength in terms of breaking length was measured according to DIN ISO 1924/2 and burst strength according to DIN ISO 2758. The results are given in the table 2 as burst index and breaking length, respectively.

The amount of dry strength agent in the white water serves as indicator of its self-retention capability. It was determined by photometric analysis of the starch/iodine complex in the supernatant of a centrifugated white water sample after the wet end system has reached equilibrium (45 minutes). The results were diminished by the starch amount found for the control trial (no dry strength product added) and recalculated to dry strength product concentration, taking into account the respective starch content.

Table 2

Dry strength agent		control without agent	Ref. Ex. 1	Ex 1	Ex 2	Ex 3	Ex 4
Addition rate	% dry on paper	-	2	2	2	2	2
Product in W/W	mg/l	-	63	43	8	58	38
Breaking length, M/D	km	3,68	4,42	4,34	4,55	4,41	4,54
rel. change	%	-	+20	+18	+24	+20	+23
Breaking length, C/D	km	1,59	1,78	1,84	1,93	1,87	2,00
rel. change	%	-	+12	+16	+21	+18	+26
Burst Index	kPas* m²/g	1,45	1,51	1,72	1,76	1,70	1,89
rel. change	%	-	+5	+19	+22	+17	+30

Breaking length: The length of a paper stripe in meters that is just self supporting until rupture.
Breaking length M/D in machine direction
Breaking length C/D in cross direction.
Product in W/W: agent found in white water;
As the results show the modified starch containing product of the present invention has in particular improved retention over reference example 1, that is less product found in white water. Moreover, it imparts higher strength to paper, which becomes most evident in burst strength.

Example7

This example is to demonstrate the superior performance of the modified starch containing product according to the invention in comparison to products obtained by reacting native starch with PAAE resin in aqueous suspension in accordance to EP 972 1110 B1 .
Papers of 100 g/m² where prepared in the same manner as described in example 6. The furnish was a mixed waste consisting of 30 % news print, 30 % magazines, 20 % OCC (old corrugated container) and 20 % CTMP (chemico-thermomechanical pulp).

The dry strength agent according to example 5 of the present invention and reference example 2 were applied in amounts of 1, 2 and 3 % dry on dry furnish. Evaluation of the tests was done in the same way as described in example 6, the results are listed in table 3.

Table 3

Dry strength agent		control without agent	Ref. Example 2			Example 5
Addition rate	% dry on paper	-	1	2	3	1	2	3
Product in W/W	mg/l	-	46	118	199	19	19	48
Breaking length, C/D	km	1,70	1,86	1,98	2,11	1,94	2,09	2,08
rel. change	%	-	+9	+16	+24	+14	+23	+22
Breaking length, M/D	km	3,81	3,68	3,93	4,33	3,81	3,61	4,01
rel. change	%	-	-3	+3	+14	0	-5	+5
Burst Index	kPas*m ²/g	1,37	1,36	1,53	1,58	1,30	1,55	1,66
rel. change	%	-	-1	+11	+15	-5	+13	+21

As the results clearly show, in particular, the retention is significantly improved.

Claims

Process for the production of a modified starch containing product comprising modifying a starch containing product with a polyaminoamide epihalohydrine resin at gelatinizing conditions at a dry content of at least 50 weight percent.
Process according to claim 1, further comprising comminuting the resulting mixture.
Process according to claim 1 or claim 2, wherein the dry content is at least 60 weight percent.
Process according to any of the preceding claims,
wherein the temperature during the gelatinizing conditions exceeds 90°C.
Process according to any of the preceding claims,
wherein the modification is carried out under a specifical mechanical energy input of from at least 30 Wh/kg.
Process according to any of the preceding claims,
wherein the modification is carried out in an extruder.
Process according to any of the preceding claims,
wherein the pH-value of the reaction mixture is of from 3 to 8.
Process according to any of the preceding claims,
wherein the starch containing product is a cereal flour.
Modified starch containing product obtainable by the process according to any of the claims 1 to 8.
Modified starch containing product according to claim 9,
wherein the modified starch containing product has a dry content of at least 80 weight percent based on the content of starch containing product and polyaminoamide epihalohydrine resin.
Modified starch containing product according to any of claims 9 or 10,
wherein the content of polyaminoamide epihalohydrine resin based on starch containing product inclusive its natural water content is of from 1 to 20 weight percent.
Modified starch containing product according to any of claims 9 and 11,
wherein the product is in granular form.
Use of a modified starch containing product according to any of the claims 9 to 12 in paper making.
Use of a modified starch containing product according to any of the claims 9 to 13 as a dry strengths agent in paper making.
Process for the production of paper comprising adding a modified starch containing product according to any of the claims 9 to 14 to a stock containing cellulosic fibers and dewatering the stock to obtain paper.