CA2004308A1

CA2004308A1 - Procedure for the manufacture of a mixture of starch and polyvinyl alcohol and thus manufactured mixture

Info

Publication number: CA2004308A1
Application number: CA002004308A
Authority: CA
Inventors: Willy A.M. Nachtergaele; Jan H. Van Nuffel
Original assignee: Tate and Lyle Europe NV
Current assignee: Tate and Lyle Europe NV
Priority date: 1988-12-09
Filing date: 1989-11-30
Publication date: 1990-06-09
Also published as: JPH02202528A; FI895838A0; EP0374993A3; EP0374993A2; ES2068887T3; EP0374993B1; BE1002635A6; FI99020B; FI99020C; DE68920012T2; ATE115605T1; US5032337A; DE68920012D1

Abstract

EXCERPT
"Procedure for the manufacture of a mixture of starch and polyvinyl alcohol and thus manufactured mixture".

to 95 parts by weight starch and 5 to 50 parts by weight polyvinyl alcohol with a degree of saponification between 87 and 100% are thoroughly mixed and furthermore the moisture content of the mixture is regulated between and 25 weight %. Subsequently the mixture obtained is subjected to a thermo-mechanical treatment at a temperature situated between 110 and 180°C. During the extrusion the mixture is subjected to shearing forces so that the product obtained when it is dispersed in cold water and subsequently is centrifuged, divides into a watery phase and a coacervate phase without a sediment of undissolved polyvinyl alcohol being formed.

Description

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20~308 "Proeedure for the manuEaeture of a mixture of s~areh and polyvinyl aleohol ancl thus manufaetured mixture".

The invention relates to a proeedure for tne ma}lufacture of a mixture of stareh polyvinyl aleohol.
It is known that polyvinyl aleohol in different applieations sueh as adhes:ives, sizlng agent for threads, water dissolva~le films and paper coating, exereises a positive influenee on the funetional properties of the prepared produets.
The polyvillyl alcohol employed can moreover vary in pro~erties depending on the applieation. These properties are deter~ined by the degree of hydrolysis and the molecular weight of the product.
In most cases the polyvinyl alcohol needs to be heated sufficiently long in order to bring the product completely into solution.
Furtherl!lore il fre~uently oecurs that polyvinyl alcohol is employed in combination with stareh cderivatives which are soluble or aispersible in cold water.
This is among others the ease in the paper coating compositiorls in which in practiee mixtures of stareh and polyvinyl aleohol are applied.
Such mixtures exert, in the presence of optical whiteners, an advantageous influenee on the whiteness oE
the paper. ~loreover the starch as a solution or otherwise is adcled to the size of whiteners. However a polyvinyl dispersion must first be manufaetured which is then heated in order to dissolve the polyvinyl alcohol.
The starch can also be added direetly in dry form to the size of optieal whiteners. In the paper eoating seetor for that matter it is the trend to ehange over to superior dry materia] eoatings.
The adclitlorl of a modified s-tareh in dry form to a - . - . . .

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pigment size, with the intent:ion of raising the dry material content of the coating composition, was already described in US-A-4 425 452. This method of~ers as ad-vantacJe that during the dry:ing o:E the coated paper less moisture naeds to be evaporated, which results in a more econolllical procedure. According to this patent no use is made however o~ polyvinyl alcoho:L.
In the above mentioned application but also in many otller applications it would thus be very advantageous that tl1e po]yvirlyl alcohol would be very c3uickly soluble in colcl water whereby -then for example Eor the manu~acture of a paper CO~til1CJ the polyvlnyl alcohol could also be added directly in dry form -to the pigmellt slurry. On the one lland therefore the coating instal:l.ation would be simplified because no solution and heating installation Eor tlle starch and the polyvinyl alcohol are necessary. On the other hand a coating agent with a lligher dry material content would be obtained -through which during the drying ol tl1e coa-ted paper less energy needs to be employed in order to evaporate the superfluous moisture and/or throuyh wllicl1 the speed of the coater can be increased.
~ cold soluble polyvinyl alcohol, whetheI or not in combill2tiol-l witl- an starch or a deri~ative thereof, is nevertheless not yet knownO
Tlle purpose of the inventiol1 now is to p~ovide a procedure for -the manufacture of a mixture of starch and polyvinyl alcohol whereby a mixture is obtained that is solubl~ in cold water.
For this purpose 50 to 95 par-ts by weight starch and 5 to 50 parts by weight polyvinyl alcohol are thoroughly mixed, furthermore the moisture content of the mixture is regulated between 10 and 25 weight ~ and subsequently the mixture is suhjected to a thermo-mechanical treatment at a temperature situated be-tween 110 and 180C, with which treatment this mixture is subjected to shearillg forces such that the product obtained, when it is dispersed in cold water and subsequently centrifuged, divides into a watery phase and a coacervate phase without a th:ird ph~se consisting o~ a sediment of undissolve~

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~00~3(~8 polyvinyl alcohol heing formed.
In a particular embodiment of the procedure a continuous extrusion is performec1 as thermo-mechanical treatment.
In a notable embodiment of the invention the moisture content is regulated between 12 and 20 weight %
during the mixing of the starch and t~e polyvinyl alcohol.
In a functional embodiment of the invention a polyvinyl alcohol with a degree of saponification between 87 and 100~ is employed.
In paper coating strongly saponified polyvinyl alcohol is preferably applied.
The starch employed can be a natural or modified starch. The modified starch can be etherified or esterified and/or oxidatively, by acid or en~ymatically broken down.
A granular etherified starch is preferably employed.
In another embodiment of the invention an acid is added to the mixture in order further to break down the starch.
The inventiorl also relates to a mixture of starch and polyvinyl alcollol obtained according to tlle pxocedure according to one of the aforementioned embodiments.
Other details and advantages on the invention will appear from the following description of a procedure for the manufacture of a mixture of starch and polyvinyl alcohol and of a thus manufactured mixture, according to the invention; this description is only given as an example and does not restrict the invention.
For the manufacture of a mixture of starch and polyvinyl alcohol according to the invention, 50 to 95 and preferably ~5 to 90 parts by weight starch and 5 to 50 and preferably 10 to 15 parts by weiyht polyvinyl alcohol are thorollghly mixed.
The polyvinyl alcohol has p~eferably a minimum degree of saponification of 87%~ This degree of saponification can go to 100~ and particularly for use in paper c~oating strongly saponified polyvinyl alcohol is preferably employed.

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~ g~30a The starch can be natural or modified.
rrhe modified starch can be etherified or esterified and/or be oxidatively, by acid or enzymatically ~roken down. A granu]ar etherified starch is pre~erably employed.
The moisture content of the mixture is regulated hetween 10 and 20 wei(3ht %, preferably between 12 and 20 weight % an~ best between 14 and 18 weight %.
The rnixture ob-tained ig subjected to a thermo-mechanical treatment at a temperature situated betweell 110 and 180C.
During this trea-l:ment the mixture is sub~ected to a shearing force so that the product obtained, when it is dispersed in cold water and subsequent]y centrifuged, divides into a watery phase and a coacervate phase without a third phase consisting of a sediment of undissolved polyvinyl alcohol being formed.
~ similar phase would be formed without or without sufEicient thermo-mechanical treatment.
A suitable thermo-mechanical treatment is a continuous extrusion.
This extrusion can be performed in an extrusion apparatus that contains a cylinder witl- one or more rotating screws which give a buildup of pressure ill the mixture, whereby the rnixture present melts througn the internal heat which is released and/or througll externally supplied heat.
The melted mixture is then trallsported by means of the screw or the screws through the pressure cyIinder toward the extremity oE the extrusion apparatus, whereby the mixture is subjected to the shearing forces. At the extremity of the pressure chamber there are one or more openings through which the mixture is pressed outward.
A suitable ex-trusion apparatus is for example an apparatus Eound on the market of the type s~ss-PR 46. Such an extruder has a capacity of 18 kg of product per hour and has a length diameter ratio of 7. The extruder contains two screws with a ~iameter of 46 mm, namely a dosing screw which rotates at 13 revolutions per minute and an extrusion screw wh;ch rota-tes at 97 revolutiolls per , ~ . . .: - - :. :
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mLnute. The time tl1e mixture stays there amounts to 10 to seconds at a temperature of between 130 and 1 50C and a pressure of between 5 and 10 kg per cm2.
Other extruders, for example of t]te type CREUSOT-I.OIRE can likewise be employed subj ect to the adjustment of the reaction conditions to the characteristics of the apparatus in order to obtain the desired shearil1g forces.
To a mixture an acid can L~ossibly be added in order furtller to break down the ' starch. The added amount oE acid is preferably selected so that the pH of a 10% suspension of the mixture is situatecl betwe,en 2 and 2.5.
It: i s surprisingly determined that with use of the extruded mixtures the polyvinyl alcohol present dissolves very well and very quickly in colcl water too.
In this way there is a clear difierence to be observed in the dissolving speed between polyvinyl alcohol witl-l a low degree of saponification, which is also considered as soluble in cold water, and extrude~ mixtures of starch and such a polyvinyl alcohol. The difference in dissolving speed is still much more clearly t:o l~e observecl when s trongly or colrlpletely saponif ied or hydrolized polyvillyl alcohol is compared with an extruded po] yvlnyl alcohol on the ba~sis of starch and such a polyvillyl alcohol .
rhe ex-truded mixtures obtained are extremely useful as a binder in coatlng compositions for the coating of E)aper. These mixtures can be added in dry form to the pigment slurry, whereby the moisture content of the mixture decreases, which of course is advantageous.
The dry material content of the thus prepared coating composition can moreover be increased with 2 to 4 weight ~6, which results in a ~ecrease of 7 to 14 weight %
of the moisture that needs to be evaporated afterward.
Furthermore it was surprisingly also determined that the applicat,ion of the extruded mixtures according to the invention as binder in coating compositions gave a significanl:ly greater whiteness to the treated paper than the corr:e~;pondil1g non-extruc1ed mixtures. These ... ... ..

, , . , : . , ~004308 non-extruded mixtures have to be boiled up beforehand. It is clear that there is question here of a synergistic efect.
Also films on the basis of extruded mixtures of starch and polyvinyl alcohol show interesting properties, such as a g~eater tensile strength and breaking length.
The invention will be further explained herea~ter with the help of some examples.
Examples 1 throuqh 5 25 kg of etheri~ied starch, brought on-to the market by the depositor under the nallle of AMYLUM A2, are placed in a mixer and stirred ~or 5 minutes.
A~ter that the moisture content and pH are determilled .
To the starch that has a moisture content of 13.2%, is then added an amount of completely hydrolized (98%) polyvinyl alcohol with low viscosity, obtainable on the market under the narne of AIRVOL 107(r) o~ Air Products in the ratio according to the following table 1.
The whole is further homogen:ized and is subsequently mixed with tl1e necessary amount of de~nitleralized water in order to obtain the desired mo;sture content according to table 1.
~ inally the ho~nogenized mixture is measured into doses by means of a dosing screw in an extrusion apparatus of the type CREUSOT~LOIRE EXTRUDER. The mixture is extruded under the extrusion conditions according to the following table 1. In this H.S. indicates a screw with kneading elements and L.S. a standard screw.
After extrusion the mixture obtained is ~inely ground.

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2~0~ 08 table 1 example 1 2 3 4 5 Composition mi xture starch 90 90 50 50 90 PVA 10 'lO 50 50 10 moisture 20 ~ 2 20 12 20 ex trusion condi tions rotation speed screw (rpM) 100 150 150 100 100 conf iguration H. S . L . S . H. S . L . S . L . S .

Examples 6 throuqh 8 The proced~lre accordiny t-~ example6 1 through 5 is repeated but with the composition of the nlixtures and the extrusioll conditit>ns as in the ollowin~ table 2, whereby moreover togetller with the demklera1ized water for the adjustment of the molsture content also 4 weight concentrated sulfuric acid, calculated on the amount o starch, is added.
After the extrusion sodium bicarbonate is added to the extruded mi~{ture in order to neutralize the acid present.
Example 8 is only taken for comparison since there is no PV~ present and therefore fall6 outside of tlle inventiOD.

200~3()l3 a -table 2 Example 6 7 8 Compositi.on mixture starch 90 90 100 moisture 12 15 15 extrusion conditions rotation s~eed screw (rpm) 150 100 100 screw conflguration H.S. L.S. L.S.

(Il.S. is a screw with kneading elements and L.S. astandaId screw).
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: Examples 9 and 10 Tlie procedure according to examples 6 through 8 is ~: repeated but with the composition of the mixtures and the ext:rusion conditions as in the following table 3 and furthermore with another type of polyvinyl alcohol, namely an only: partially hydrolized (88-90%) polyvinyl alcohol with low viscosity that is obtainable on the market under the name of AIR~OL 203 (r) of Air Products.

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table 3 Example 9 10 Composition mixture stareh 50 90 m~isture 16 16 extrusion conditions rotatiol1 speed screw (rpm) 100 100 screw configurati.on I.,S. L.S. (standard screw) Results The extruded mixtures obtained according to the examples described above were dispersed in cold water, in a eoncerltration of 5 weight % and stirred for 3 minutes.
T}le dispersed mixtures were subsequerltly centrifuged for 10 minutes at 3000 revolution per minu-te.
: Por comparison the following mixtures which were not:
prepared aceording to the invention and thus were not extru~ed, were likewise dispersed and centrifuged:
Example 11 parts ~y weight starch AMYLUM A2 prepared according to the proeedure from example 8 with a moisture content of 15~ and 10 parts by weight polyvinyl alcohol :~ AIRVo~ 107 tr)~
Example 12 parts by weight starch AMYLUM A2 prepared aceording to the proceduxe from example 8 with a moisture eontent of 15% and 50 parts by weight polyvinyl aleohol AIRVOL 107 (r).
Example 13 : 90 parts by weight starch AMYI.UM A2 prepared :
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2()04308 according to the procedure from example 8 with a moisture content of 15% and 10 parts by weight polyvinyl alcohol AIRVOL 203(r).
In table 4 shown hereafter the viscosities of the dispersions and the centrifuge results are shown.
The distribution of the various phases are shown in percentages.

table 4 Example ViscosityMoisture Gel Sediment in mP %

~2 50 50 An additional test was performed on the layer of viscous mixtures in order to verify to what extent the polyvinyl alcohol present was disso]ved.
uring this the sample material was dispersed in cold water under violent stirring. The concentration of the dispersions amounted to 28~ dry material. The dispersions obtained were then filtered through a 53 micron sieve. The residue on the sieve was then dried and weighed. The residue was expressed as a percentage of the amount of dry material used. The residual polyvinyl alcohol content was then determined from the difference .
., : ,~ , , " :: ,, : " , - ~ ~ ~-: : - : : :
:. , , ~: , ,. .: ., , : ., ~)0~3()8 with a referance sample, which contained no polyvinyl alcohol. The results are shown in the following table 5.

table 5 residue residual polyvinyl alcohol 6 0.7% 2.7%
7 0.8~ 3.9%
0.56% 1.3%
11 ~.45~ 80.2%
13 1.35% 9.0 reference 0.43%

The residual polyvinyl alcohol was expressed as a pexcentage of the polyvinyl alcohol present, which is not dissolved.
From table 5 it clearly appears that the polyvinyl alcohol present with the examples according to the invention is practically completely dissolved. In the case that partially hydrolized polyvinyl alcohol was employed it appears that here also the solubility is greatly proved. .
~ pplications.

"Coating"~ compositions were produced hy means of products according to the invention and compared with known compositions.
Moreover the dry material and the viscosity of the "coating" mixture, as well as the dry material after dilution of the pigment size were determined at 1000 mP.
After treatment of the paper with this composition the whiteness was measured with the assistance of a Hunterla~
apparatus.
The products of the invention were added to the "coating-premix" in dry form. In the other cases the hinder or co binder had to be dissolved ~eforehand with - , . ~ : . :.
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~00~3(~8 exception of the extruded starch from example 8.
In the following examples the followiny precoating composition was employed:
pigment : 80 parts calcium carbonate (Hydrocarb go ~
20 parts China clay (Arnazon a8)(r) binder : 8 parts styrene butadiene latex (DL
685)(r) additive : 1 part Urecoll(r) 1 part calcium stearate 1.5 parts optical wllitener (Blancophor P) This size has a dry material content of 72.0~.
The added materials and the results obtained are sho~1 in the following table 6:

table 6 . _ composi- binder parts %d.m. visco- ~d.m.
whiteness tion (1) sity (2) mP
I latex 2 69.0 2450 65.0 90.9 CMC
II latex 2 67.4 920 67.4 90.8 IRVOL 107(r) III from ex. 8 4 72.5 3000 66.3 89.7 IV from ex. 7 4 72.5 1840 69.3 92.2 V from ex.10 4 72.5 2560 68.2 91.4 VI from ex.11 4 70~5 2500 66.7 90.8 VII from ex.13 4 70.5 2200 67.0 90.9 (1) before dilution.
(2) after dilution to 100n mP.

From the above table it therefore clearly appears that in the case of the compositions IV and V "coating"
mixtures are obtained with a distinctly higher dry .~

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material, when compared with the compositions I and II.
In addition to this the greater whiteness for paper "coated" with this composition is striking; a gain of 0.5 I:o 1% in whiteness is considered as a great advantage in the paper industry.
Another application exists in manufacturing water soluble films.
A water soluble film manufactured on the basis of the mixture o~ starch and polyvinyl alcohol manufactured according to the above mentioned exaMple 2 wa~ compared with a pur~ polyvinyl alcohol film (polyvinyl alcohol AIRVOL 203(r)) and with a ~ilm on the basis of a mixture with the same composition as in example 2 but without the extrusion according to the invention.
The mixture of the pure polyvinyl ~lcohol was boiled up beEorehand. The composition according to example 2 was stirred up in cold water an~ used as such.
Tlle collcentration of the solution amounted to 10%.
The spread out solutions were leEt to dry in the air.
The tensile strength, the breaking length and the elongation capacity of the films obtainec1 is showll in -the followirlg table 7.

table 7 fillD weight tensile breakiny elonga-thickness (g/m2) strength length tion ~mm) ~daN) (km)(~m~

(1) 0.063 74.18 2.23 2.0021.7 ex. 20.056 78.25 3~21 2.801.5 mixture 0.062 86.25 2.041.60 1.7 : ~ :
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(1) AIRVOL 203(r) The invention is in no way restricted to the embodiments describec1 above and within t:he scope of the patent .
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application many changes can be applied to the described embodiments, among others regarding the choice of the raw materials and the apparatus employed.

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Claims

1. Procedure for the manufacture of a mixture of starch and polyvinyl alcohol, characterized in that 50 to 95 parts by weight starch and 5 to 50 parts by weight polyvinyl alcohol are thoroughly mixed, furthermore the moisture content of the mixture is regulated between 10 and 25 weight % and subsequently the mixture obtained is subjected to a thermo-mechanical treatment at a temperature situated between 110 and 180°C, with which treatment this mixture is subjected to shearing forces such that the product obtained, when it is dispersed in cold water and subsequently centrifuged, divides into a watery phase and a coacervate phase without a third phase consisting of a sediment of undissolved polyvinyl alcohol being formed.

2. Procedure according to claim 1, characterized in that a continuous extrusion is performed as thermo-mechanical treatment.

3. Procedure according to one of the claims 1 and 2, characterized in that the moisture content is regulated between 12 and 20 weight % during the mixing of the starch and the polyvinyl alcohol.

4. Procedure according to claim 3, characterized in that the moisture content is regulated between 14 and 18 weight % during the mixing of the starch and the polyvinyl alcohol.

5. Procedure according to one of the claims through 4, characterized in that a polyvinyl alcohol with a degree of saponification between 87 and 100% is employed.

6. Procedure according to one of the claims through 5, characterized in that a mixture is manufactured of 85 to 90 parts by weight starch and 10 to 15 parts by weight polyvinyl alcohol.

7. Procedure according to one of the claims through 6, characterized in that as starch a granular etherified starch is employed

8. Procedure according to one of the claims through 7, characterized in that an acid is added to the mixture in order further to break down the starch.

9. Procedure according to claim 8, characterized in that the acid is so selected that the pH of a 10%
suspension of the mixture is situated between 2 and 2.5.