CH616963A5 - Process for the production of fibrillated structures made of synthetic resin - Google Patents

Abstract

Fibrillated structures made of synthetic resins such as polyolefins are obtained by sudden decompression of a mixture of molten polymer and solvent. The mixture additionally contains a monomer capable of being grafted onto the resin, such as maleic anhydride. The decompression is performed through an appropriate orifice at elevated pressure and temperature conditions. The fibrillated structures obtained are employed together with cellulose fibres, towards which they exhibit good reactivity. Papers manufactured in this way have an excellent breaking length.

Description

The present invention relates to a process allowing the grafting on the polymer before the sudden expansion.

Direct production, from synthetic resins, of structure It has in fact been found that the mixture of molten polymer and fibrillated res which are capable of binding with the celluiosi- solvent fibers is at the time of its relaxation in conditions which therefore lead to the production, from pressure and temperature conditions which promote the grafting of the mixture of these structures and of cellulose pulps, of papers Qu of the incorporated monomers.

mixed with improved characteristics. 55 The polymers used can be any and,

Various methods are currently known for producing titles of non-limiting examples, mention may be made of polyolefins, fibrillated structures from thermoplastic syn-polyamides, polyesters, polyurethanes, spun polycarbonates. tes, vinyl polymers and acrylic polymers and

One of the most elegant techniques is to relax blends of these polymers. However, it is preferable to abruptly put through a suitable orifice, a mixture of 60 polyolefins such as for example the polyethylene of molten polymer and of solvent being under high or low density conditions, polypropylene, polystyrene, temperature and pressure such as expansion causes poly-4-methylpentene-1, syndiotactic polybutadiene, instantaneous vaporization of the solvent and solidification of 1,4-polybutadiene etc. Preference is given to the mother polyolefins in the form of a fibrillated structure, possibly tinned, derived from olefins comprising from 2 to 6 carbon atoms quetée. This technique is explained in detail in particular in 65 in their molecule. Excellent results have generally been Swiss patents No. 513 217 of October 27, 1969, 562,887 and with polyolefins derived from ethylene and / or propylene.

553 856 of 4.8.1972 as well as in Swiss patent n ° 599 986 The grafting monomers are preferably in the name of the holder. As a variant, the mixture of monomeric polymers having a double bond and groups

3

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susceptible to react with hydroxyl groups of cellulose and difficult to homopolymerize.

To this end, preference is given to acrylic and methacrylic monomers such as alkyl and glycidyl acrylates and methacrylates, α-chloracrylic acid, etc. as well as allyl monomers and unsaturated polycarboxylic acids such as maleic, fumaric, itaconic acids etc. and their derivatives such as the corresponding anhydrides.

The best results can be obtained with maleic anhydride. The amount by weight of polar graftable monomers present in the mixture subjected to the sudden expansion can vary between 0.1 and 50% and preferably between 0.2 and 10% by weight of the polymers which are present there.

The grafting of these monomers before sudden expansion can be induced by free radicals generated for example by high energy radiation.

However, it is preferred to cause this grafting by the introduction into the mixture of molten polymer and of solvent of a compound generating free radicals.

Many types of free radical generators can be used in the context of the invention. By way of examples, mention may be made of organic peroxides such as ditert.butyl, lauroyl, benzoyl, acetylcyclohexanesul-fonyl peroxides, peroxydicarbonates such as diethyl and diketyl peroxydicarbonates, peresters such as perpivalate tert.butyl and azo-bis-nitriles such as azo-bis-2,4-dimethyl-levaleronitrile, azo-bis-isobutyronitrile etc. Preference is however given to free radical initiators with a half-life of approximately 10 minutes at 160 ° C.

The amount of initiators used can vary between 0.01 and 5% and preferably between 0.05 and 1% by weight of the polymer or polymers present in the mixture.

The grafting time, that is to say, the period of time during which the grafting monomer is in the presence of the mixture of molten polymer and solvent at high temperature and pressure before sudden expansion can vary between 10 seconds and 120 minutes, and preferably between 30 seconds and 12 minutes. However, durations longer than 120 minutes are by no means excluded.

With regard to the choice of solvent and of the expansion conditions, reference will usefully be made to the data set out in the aforementioned French patents and patent applications which remain applicable. The same applies as regards the characteristics of the expansion orifices and of the means which can be used to directly obtain the fibrillated structure in the form of distinct short fibrils. It should also be borne in mind that in the process according to the invention the solvent can be replaced in whole or in part by water. The meaning of the word solvent must therefore be broadened to include water.

Depending on the solvent chosen, the grafting can be carried out either completely in solution when all the constituents of the mixture are soluble in it under the conditions of expansion or in a two-phase system when the grafting monomer or monomers are not soluble in the solvent but are dispersed therein as an emulsion. It is preferable to operate in a two-phase system because this has the effect of reducing any risk of homopolymerization of the graftable monomer (s) since the free radicals generated act only at the monomer-polymer solution interface.

According to another alternative embodiment, the mixture subjected to expansion may also advantageously contain a proportion relative to the weight of polymer of 1 to 9% and, preferably 5 to 40% by weight of a starch, of cellulose or cellulose acetate etc. It has in fact been found that the esterification of the reactive groups of these compounds via the reactive groups of the graftable monomer (s) can be carried out directly under the conditions of the mixture before expansion. In order to promote this esterification, it is also possible to introduce into the mixture a concentrated organic acid such as acetic acid. By operating in this way, fibrillated structures are usually obtained directly on which particles of cellulosic nature are fixed, which make them easily wettable and which promote their attachment to cellulosic fibers.

The mixture of polymer and solvent can furthermore contain other usual additives such as stabilizers with respect to the action of heat or light, reinforcing agents, fillers, pigments, dyes, antistatic agents, nucleating agents etc.

The process described does not usually pose any particular problem during its application in a discontinuous process for the production of fibrillated structures. In addition, it can be very easily applied within the framework of the integrated continuous process such as that which is the subject of the French patent 1,596,107 mentioned above and which protects the coupling of the production process of 20 fibrillated structures by the technique sudden expansion with an olefin polymerization plant. Generally, it suffices, in this case, to introduce the adequate amounts of polar graftable monomer and of the other optional ingredients into the polymer solution present in the dissolving tank, that is to say before the packaging of the solution for abrupt relaxation. This integration can therefore be carried out without affecting the productivity of the installation.

The fibrillated structures obtained according to the process according to the invention can be very easily suspended in water because the grafted monomer gives them a highly hydrophilic character. These structures can also be easily suspended in other media such as, for example, chlorinated solvents.

35 In addition, the mixture of these fibrillated structures with conventional cellulosic pulps leads to papers having properties, and in particular a breaking length, which are often greater than those of papers produced solely from these cellulosic pulps, which proves that their chemical reactivity 4o vis-à-vis cellulosic fibers is significantly improved. However, in order for the chemical bond between the two types of products brought into contact to occur, it is generally advisable to subject the papers formed to thermal consolidation at a relatively high temperature capable of causing at least a partial melting of the fibrillated structures.

This heat treatment can, however, be avoided and nevertheless obtain an effective bond by reacting the grafted fibrillated structures in the presence of cellulosic fibers in suspension in an anhydrous organic solvent containing an acidic esterification catalyst.

The thermal consolidation treatment can also be avoided if a highly mobile hydroxylated coupling agent is incorporated into the mixture of reactive grafted fibrils and cellulosic fibers suspended in a liquid.

55 As coupling agents suitable for the process according to the invention, mention may in particular be made of starch and its derivatives, cellulose derivatives, polyvinyl alcohols with a high hydrolysis rate and of low molecular weight, polyethylene glycol. , polypropylene glycol, a nitrogen derivative such as 60 casein.

The suspending medium can be water or an organic solvent dissolving the coupling agent.

The amount of coupling agent used can vary between 1 and 50% by weight of the dry weight of the fibrils used.

By operating in this way, it can be seen that the papers produced have good mechanical properties to the point that thermal consolidation is no longer essential. he

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4

However, it turns out that if an adiabatic expansion is nevertheless carried out through a thermally disturbed die, breakthrough lengths are obtained in this case, as described in the French patent, the demand for remarkable. French patent 75 00 904 filed on 13.1.1975. The duration of

Furthermore, when the structures are dispersed, the test is 139 minutes and the product obtained is presented in fibrillated according to the invention or even when mixed 5 in the form of short fibrils.

with cellulose pulp, one can also incorporate into the From a Kraft cellulose pulp two preparations are prepared for dispersing the compounds capable of reacting both paper samples, one from a mixture of 70 parts with the hydroxyl groups of cellulose and with the dry weight of cellulose pulp and 30 parts by dry weight of reactive groups of the grafted monomer (s). For this purpose, conventional fibrils prepared from a 95/5 mixture of for example, the incorporation of a polyamide modified by 1 (l polypropylene and polyethylene and the other from an example by epichlorohydrin or a urea-formaldehyde mixture of 70 parts by dry weight of cellulose pulp and dehyde proves to be very advantageous. parts by dry weight of the fibrils obtained according to the example.

The process according to the invention is further illustrated by After thermal consolidation at 170 ° C., the following practical examples are measured. bursts of rupture of the two paper samples and we note i 5 the respective values of 4430 m and 4820 m.

Example 1

Grafting in a homogeneous solution Example 4

A solution of polypropylene in chloride is prepared. The procedure is as in Example 3 except for the fact that the methylene in the presence of 5% by weight of maleic anhydride mixture of high density polyethylene and polypropylene is relative to the polymer , the polymer mass fraction being replaced by a mixture in the same proportions of 10% polyole. The mixture brought to 190 ° C. and to a high density thylene and syndiotactic polybutadiene is incorporated into the mixture and that pressure of 80 kg / cm 2 0.5% by weight of acrylic acid peroxide is replaced by anhydride maleic to

tert.butyl with respect to the polymer. The solution is then relaxed by 1% by weight relative to the weight of the polymers. The due adiabatically through an orifice of 1 mm in diameter the rupture lengths measured on the two samples are and from height to atmospheric pressure. The duration of 25 respectively 4430 and 5620 m.

the test is 60 minutes and the product obtained is in the form of short fibrils. Example 5

From a Kraft cellulosic pulp refined at 20 ° Schop- We operate as in Example 3 apart from the modifications per we prepare three paper samples, one from the following pure cellulosic pulp, the second from of a mixture of 70 parts 30 - the acrylic acid is replaced by maleic anhydride by dry weight of cellulose pulp and 30 parts by dry weight of at a rate of 1% by weight relative to the weight of the polymers, fibrils conventional polypropylene and the third from a - is incorporated into the mixture 10% by weight relative to mixture of 70 parts by dry weight of cellulose pulp and 30 to powdered cellulose polymers.

parts by dry weight of fibrils obtained according to Example 1 and The breaking lengths measured on the two samples, the breaking length of the samples after consolidation is measured is 4430 m (conventional polyethylene fibrils and thermal donation at 170 ° C. The values noted are respective (of propylene) and 5400 m (fibrils according to the example).

4320 m, 3370 m and 4660 m.

Example 6

Example 2 The procedure is as in Example 5 except for the fact that the

Grafting in dispersed phase 40 cellulose is replaced by an equal weight of starch grading 50%

A solution of polypropylene in amylose pentane is prepared. The measured rupture lengths are respectively in the presence of 0.5% by weight of maleic anhydride (phase 4430 m and 5825 m.

dispersed) relative to the weight of polymer, the mass fraction of polymer being 15%. Incorporated into the mixture Example 7

brought to 180 ° C and at a pressure of 65 kg / cm2 0.05% by weight "A solution of polypropylene in pentane of di-tert.butyl peroxide is prepared relative to the polymer. The in the presence of 5% of maleic anhydride (dispersed phase) per solution is then relaxed as in Example 1. The duration relative to the weight of polymer, the mass fraction of polymer in the test is 60 minutes and the product is in the form of being 15%. It is incorporated into the mixture brought to 180 ° C. and with short fibrils. a pressure of 65 kg / cm2,0,5% by weight of di-peroxide

From the cellulose pulp of Example 1, a tert.butyl is prepared relative to the polymer. The solution is then a sample of paper titrating 30% by dry weight of relaxed fibrils as in Example 1. The duration of the test is 60

obtained according to Example 2. The breaking length of minutes and the product is in the form of short fibrils,

the sample after thermal consolidation at 170 ° C. amounts to From a Kraft LAPONIA cellulose pulp refined at

5370 m. 19 ° Schopper and fibrils following the example in a report

55 weight 70/30 a suspension is made in water containing

EXAMPLE 3 11.6% by weight relative to the weights of the friend fibrils

A solution of high density polyethylene and cationic donation is prepared. From this mixture, polypropylene samples are made in a 95-5 weight ratio in paper ions.

technical hexane in the presence of 1% by weight of acrylic acid. Table I below gives the length values of that, relative to the weight of polymers, the mass fraction at break of the sheets thus obtained with or without treatment. of polymers being 15%. It is incorporated into the mixture brought to thermal consolidation. The table also gives 195 ° C. and at a pressure of 70 kg / cm 2 1% by weight of peroxide of comparative values for a purely cellulosic and di-tert.butyl sheet with respect to the polymers. The solution is then for a sheet prepared in the absence of cationic starch.

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Table I Unconsolidated sample

consolidated at 125 ° C

consolidated at 170 ° C

Length% Length% Length%

reference reference reference rupture rupture rupture m

m

Pure cellulosic paste (reference) 3880 100

Cellulose pulp + grafted fibrils 70/30 2600 67

Cellulose paste + grafted fibrils 70/30 +

cationic starch 3320 86

3400

88

5500

6380

142

164

Example 8

This example relates to a continuous production technique.

A mixture containing continuously is prepared and using a mixer

-100 parts by weight of ELTEX A1050 (polyethylene with a density equal to 0.965 manufactured and sold by the Holder

- 5 parts by weight of maleic anhydride of technical quality

- 0.5 parts by weight of ditert.-butyl peroxide.

The mixture is pneumatically introduced into a tank fitted with an agitator and suspended at a temperature of 40 ° C. in technical hexane. The injection rates are 20 kg / h for the mixture and 2701 / h for the solvent. A regulation makes it possible to maintain a constant level in the tank and a constant ratio between the quantities of the constituents.

This suspension is continuously extracted from the tank and is compressed to 80 kg / cm2 and then heated to 200 ° C by passage through a tubular heat exchanger. The solution thus obtained is filtered and then relaxed by passing through a shredding die whose diameter of the expansion orifice is 1 mm and of the type described in Belgian patent 824 844 filed on 17.1.1975 by the Holder.

The residence time of the solution at 200 ° C is 60 seconds.

Discontinuous fibrils are obtained which are collected either in the form of a dry sheet in an apparatus as described in Belgian patent 787,890 filed on 23.8.1972 by the Holder, or in the form of an aqueous suspension in an apparatus such as described in Belgian patent 811 778 filed on 1.3.1974 by the Holder. In the latter case, the suspension after a conventional papermaking process is wound in the form of a carton. Mixed papers are prepared containing 70 parts by dry weight of cellulose pulp (Kraft Laponia refined at 20 ° SR) and 30 parts by dry weight either of fibrils such as obtained according to the technique which has just been described or of fibrils prepared according to the same procedure but in the absence of maleic anhydride and ditert-butyl peroxide. The table below gives the breaking lengths of the sheets thus obtained.

Table II Sample

Breaking lengths: m unbound

cellulosic pulp 45 + non-grafted fibrils 2380 cellulosic pulp + grafted fibrils (ex. 8) 3010

thermally consolidated at 126 ° C

2460 3795

thermally consolidated at 135 ° C

3890 6465

VS

Claims (10)

616963 1. Process for the direct production of aqueous fibrillated structures of molten polymer containing a solvent. synthetic resin capable of binding with celluiosi- Pastes obtained by these techniques can ques by sudden expansion through an appropriate orifice to present either in the form of continuous fibrillated structures or mixture of molten polymer and solvent found in 5 in the form of shredded structures of short length and conditions of pressure and temperature elevated so their characteristics are detailed in the documents claim that the expansion causes the instantaneous vaporization of the cities. solvent and solidification of the polymer in the form of a structure. The fibrillated structures obtained according to these methods are, fibrillated ture characterized in that it is incorporated into the mixture after possible shredding and refining, commonly used subjected to sudden expansion at least one polar monomer, „for the production of synthetic papers although they presen-graftable on the polymer put in work and in that one provokes generally two major drawbacks. grafting onto the polymer before the sudden expansion. So these structures, because of the character generally 2. Method according to claim 1 characterized in that the hydrophobic of their constituent polymer, are hardly polymer used is selected from the group formed by suspensions in water for the production of polyolefins. 15 papers by the conventional paper channel. We can certainly remedy 2 CLAIMS melted and solvent can be replaced with an emulsion 3. Method according to any one of claims 1 or failing this by resorting to the use of surfactants but 2 characterized in that the graftable monomer is chosen from the latter often adversely affect the quality of the papers produced. group formed by acrylic, methacrylic and also monomers, when producing synthetic papers with allylics as well as by unsaturated polycarboxylic acids and from these fibrillated structures in mixture with pastes their derivatives. 2 <i cellulosics, we see that these structures, because of their 4. Method according to claim 3 characterized in that the chemical inertness behave like an inert filler and no graftable monomer is maleic anhydride. not cling to cellulosic fibers. 5. Method according to any one of claims 1 to 4 This lack of affinity between these two constituents leads to characterized in that the quantity by weight of monomers grafted to the production of mixed papers which have characteristics introduced into the mixture subjected to sudden expansion 25 ques, and in particular a breaking length, less than that varies between 0.1 and 50% by weight of polymers present in this paper made only from cellulose pulps, mixture. In order to remedy this drawback, we have already proposed in 6. Method according to any one of claims 1 to 5 Japanese patent application 48/27007 filed on 12.8.1971 characterized in that the grafting is obtained by the introduction in the name of TORAYIND INC to produce fibrils in the mixture of a free radical generator compound. 30 precipitation of a polypropylene and polypropylene solution 7. Method according to claim 6 characterized in that the lene grafted with styrene. This process in fact allows the production of free radical generator compound is chosen from the group of fibrils which can have a certain reactivity with respect to formed by organic peroxides, peroxydicarbonates, cellulosic fibers. However, this process is difficult and compli-peresters and azo-bis-nitriles. to implement and does not actually have an effect 8. A method according to any of claims 1 to 7 labeled benefit. characterized in that the mixture of molten polymer and of We have now developed a process leading directly solvent also contains from 1 to 90% by weight with respect to the production of fibrillated structures which are very weight of polymers of a compound chosen from the group formed reactive with respect to cellulosic fibers and which can be starches, cellulose and cellulose derivatives. more easily suspended in water. 9. The method of claim 8 characterized in that the 40 The present invention relates to a process for producing a mixture of molten polymer and solvent further contains a direct fibrillated structures in synthetic resin capable of concentrated organic acid. bond with cellulosic pulps by abrupt relaxation through 10. Papers obtained from a mixture of cellulose pulp with an appropriate orifice of a mixture of molten polymer and sic and fibrillated structures characterized in that they contain solvent which is under pressure conditions and temperate-fibrillated structures prepared according to claim. 45 rature such that the sudden expansion causes the instantaneous vaporization of the solvent and the solidification of the polymer in the form of a fibrillated structure in which is incorporated into the mixture subjected to the sudden expansion at least one polar monomer graftable on the polymer used and we provoke