DE102017214349B4 - Use of silylated alkyl celluloses as an adhesive - Google Patents

Abstract

Use of silylated alkyl celluloses as an adhesive.

Description

The present invention relates to the possibility of using silylated alkyl celluloses as an adhesive.

The social and political will to establish more environmentally friendly products leads to the need to develop new adhesive systems. These should be based on water as a solvent and still have high adhesive strengths. So far, water-based adhesives from z. B. Methylcellulose is only used with the use of bond strength enhancers and is mostly only used for paper bonds. Ideally, these take place in dry environments.

As a wood adhesive, methyl cellulose has been used as an additive in film-forming mixtures with other polymers ( US 2017 / 0190941A1 ) is used. Other inventions describe formulations with a large number of ingredients, some of which are suspected of being carcinogenic ( CN 106519998 A , CN 106520067 A , CN 106497189 A ).

The adhesive properties of water-based adhesives with pure methyl cellulose are not strong enough for applications that go beyond wallpaper paste or wood glue. Often, methyl cellulose is used in combination with modified starch esters. Other water-based adhesive systems use polyurethane dispersions as rubber adhesives (WO 2017/103063 A1).

Published inventions relating to trimethylsilyl cellulose (TMSC) are limited to use as particles in a polymer matrix for the production of a reactor ( WO 2017029120A1 ), as a chemical modifier in foamed polyurethanes ( EP2 03833481 ) or as a dispersant ( WO 2012/130844 A1 , EP 2 505 568 A1 ).

Other publications deal with the synthesis and characterization of trimethylsityl-methylcellulose (TMS-MC) (Xianweisu Kexue Yu Jishu (2002), 10 (4), 1-5, 12) and its properties with regard to oxygen enrichment in membranes (Huagong Xuebao (Chinese Edition) (2006), 57 (5), 1251-1254, Jinan Daxue Xuebao, Ziran Kexue Yu Yixueban (2006), 27 (5), 699-704, 709 and Liaoning Huagong (2009), 38 (12), 847 -849, 874).

Ionic liquids (IL) have so far been used for cellulose as a solvent for homogeneous reaction conditions ( DE 10 2006 029 306 A1 ). Disadvantages of this method are the high costs and risks to health and the environment from the large quantities of IL. The DE 10 2009 012 161 A1 describes the use of small amounts of an IL as an activator in a heterogeneous reaction. Cellulose was also treated with liquid ammonia, followed by silylation (W. Mormann, Cellulose, 2003, 10, 271).

The DE 69 031 151 T2 relates to chemically modified water-soluble polymers. In particular, this patent relates to a new class of silylated cellulose ethers with new and useful properties.

The DE 32 32 467 A1 relates to a process for the production of cellulose ethers with improved dispersing behavior.

From the DE 100 06 603 A1 hydrophobically modified cellulose ethers and a process for their production and their use are known.

The DE 10 057 554 A1 relates to a fastening and / or stabilizing agent for an organic material which contains a silylated derivative of a compound containing hydroxyl, carboxyl or amino groups in a non-polar solvent.

It is desirable, but not yet achieved, to develop adhesives based on cellulose derivatives which do not require the addition of bond strength promoters.

The object of the present invention is therefore to provide new adhesive compositions which are environmentally friendly and are based in particular on aqueous compositions. The adhesive compositions should exceed the adhesive effects of methyl cellulose known from the prior art and, in particular, enable use without additional bond strength enhancers.

This object is achieved through the use of silylated alkyl celluloses as an adhesive according to patent claim 1.

A silylated alkyl cellulose is understood to mean a cellulose derivative that is partially alkylated on the one hand and partially silylated on the other.

The silylated alkyl celluloses used according to the invention are preferably distinguished by a degree of substitution of alkyl groups (DS _alkyl ) between 0.5 and 2.5, preferably between 1.0 and 2.2, particularly preferably between 1.6 and 1.8.

The degree of substitution of the silyl groups (DS _silyl ) is more preferably from 0.01 to 2.5, preferably between 0.1 and 0.5, particularly preferably between 0.14 and 0.41.

The alkyl groups in question are in particular selected from the group consisting of linear or branched alkyl groups with 1 to 18 carbon atoms.

The alkyl groups are particularly preferably methyl groups; H. a silylated methyl cellulose.

wobei die Reste R¹, R² und R³ jeweils unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus C₁-C₃₀-Alkyl, C₂-C₃₀-Alkenyl, C₂-C₃₀-Alkinyl, C₃-C₁₂-Cycloalkyl, C₅-C₂-Cycloalkenyl oder Aryl, wobei diese sechs Reste ggf. substituiert sein können.Another advantageous embodiment provides that the silyl groups are selected from the group consisting of radicals of the following formula I:

where the radicals R ¹ , R ² and R ^{3 are} each independently selected from the group consisting of C ₁ -C ₃₀ -alkyl, C ₂ -C ₃₀ -alkenyl, C ₂ -C ₃₀ -alkynyl, C ₃ -C ₁₂ -Cycloalkyl, C ₅ -C ₂ -cycloalkenyl or aryl, it being possible for these six radicals to be optionally substituted.

In particular, the radicals R ¹ , R ² and R ^{3 are} each methyl groups.

According to this preferred embodiment, the present invention relates in particular to the use of trimethylsilyl-alkyl celluloses as an adhesive.

According to the invention, a trimethylsilyl-methylcellulose (TMS-MC) is particularly and very particularly preferably used as the adhesive.

In particular, silylated alkyl cellulose is used as an aqueous gel. Here, the silylated alkyl cellulose is dispersed or dissolved in water.

According to a preferred embodiment, the content of the silylated alkyl cellulose in the gel is between 1 and 80% by weight, preferably between 5 and 60% by weight, particularly preferably between 10 and 40% by weight.

The aqueous gel is preferably used with a viscosity of 0.5 to 150 Pa · s, more preferably 1 to 100 Pa · s, particularly preferably 10 to 75 Pa · s. The viscosity is determined using a 10% strength by weight aqueous gel of the silylated alkyl cellulose using a plate-and-plate viscometer.

The aqueous gel can, for example, also contain further additives selected from the group consisting of hydroxyalkyl celluloses, in particular 2-hydroxyethyl cellulose.

The aqueous gel is preferably free of bond strength enhancers, such as are known, for example, in particular in connection with methyl cellulose in adhesive compositions. Bond strength boosters are, for example, vinyl acetate-ethylene copolymers or starch ethers.

Also described is an adhesive composition in the form of an aqueous gel containing at least one silylated alkyl cellulose dispersed (or dissolved) in water.

The silylated alkyl cellulose used in the adhesive composition is identical to that for the silylated alkyl cellulose described above for use as an adhesive. All of the preferred embodiments described above with regard to the silylated alkyl celluloses and the content or physical properties of the aqueous gel also apply to the adhesive composition described.

The adhesive compositions described are particularly suitable for bonding wood, metals, glass, ceramics, paper, plastics or as wallpaper paste. Wood bonding of furniture, doors, wood paneling and decorations are particularly preferred.

The silylated alkyl celluloses can be produced in a manner known per se. In this regard, see the patent applications, for example DE 10 2006 029 306 A1 and DE 10 2009 012 161 A1 referenced, the disclosure content of which is also made the subject of the present application with regard to the manufacturing processes in question.

The present invention is described in more detail with reference to the following embodiments, without restricting the invention thereto.

Of particular interest for the present invention is the production of trimethylsilyl ethers of methyl cellulose (MC) with a silylating agent and an ionic liquid (IL) as an activator (as, for example, in DE 10 2009 012 161 A1 described) and in particular the production of gels from these and their use as adhesives. Without further additives, these adhesives should achieve a significantly higher bond strength than pure methyl cellulose.

The present invention describes in particular the use of silylated methyl cellulose and in particular of aqueous gels made therefrom as an adhesive or adhesive additive.

The silylated methyl cellulose is preferably produced in the presence of small amounts of an IL. This procedure is based on the in DE 10 2009 012 161 A1 described procedure.

In the event that the silylation of methyl cellulose according to the DE 10 2009 012 161 A1 is carried out, the amount of ionic liquid used can be used between 9 and 34 wt .-%. In particular, an ionic liquid from the group of the imidazolium compounds is used as the ionic liquid. In particular, the production reaction is carried out under heterogeneous reaction conditions, such as from the DE 10 2009 012 161 A1 described, carried out.

Methyl cellulose is obtained from cellulose, a naturally occurring polysaccharide from almost inexhaustible sources of raw materials. Cellulose is made up of β-1,4-glycosidically linked glucose units, with one molecule of water being split off with each linkage. The repeating parts of the cellulose molecule are called anhydro-glucose unit (AGU). Up to 3 functional groups can be chemically linked to the cellulose molecule per AGU. This results in a degree of substitution (DS) of a maximum of 3. The cellulose molecules are built up like a chain. The longer the chain, the higher the molar mass. This is also expressed by the degree of polymerisation (DP).

In the methyl celluloses (MC) used in this invention, the DS of the methyl groups is preferably between 0.5 and 2.5 (corresponds to a methoxy content of 8.6-44.5%). The DS of the methyl groups is preferably between 1.6 and 1.8 (corresponds to a methoxy content of 27.5-32%). The DP directly influences the viscosity of aqueous dispersions produced by MC, so instead of the DP, the viscosity of a standardized aqueous dispersion is given as the criterion (mass fraction 2% in water, at 20 ° C). The viscosities of the MC used for this invention are between 15 mPas and 4000 mPas.

The silylation of methyl cellulose (MC) is preferably carried out under heterogeneous reaction conditions in propylene carbonate. This z. B. per molar equivalent MC between 0.5 and 3.5 molar equivalents Silylating reagent and between 0.03 and 0.33 molar equivalents of an ionic liquid are used. In particular, between 1.75 and 3.5 molar equivalents of the silylating reagent and between 0.16 and 0.33 molar equivalents of the ionic liquid are used.

The silylation reagent is, for. B. to transfer a chemical compound which, under suitable conditions, is suitable to transfer a trimethylsilyl group (TMS group). The silylation reagent is preferably a nitrogen compound which has several TMS groups. 1,1,1,3,3,3-hexamethyldisilazane (HMDS) is even more preferred here.

The ionic liquid preferably comes from the group of the imidazolium compounds. More precisely, they are N-substituted imidazolium compounds. Particularly preferred around 1-ethyl-3-methylimidazolium acetate (EMImAc).

The process can be carried out in one step in a reactor system with subsequent work-up. The process dispenses with pre-treatment of the MC, e.g. alkalization with caustic soda. The MC is placed in a suitable glass jacket reactor with propylene carbonate and stirred. The silylation reagent and the IL are then added with the stirrer running. The reaction temperature is 85 ° C. and the reaction time is between 3 hours and 24 hours, preferably between 3 hours and 6 hours. After the reaction time has elapsed, it is worked up with ethanol and water by centrifugation.

The DS of the TMS-MC produced with respect to the TMS group is preferably between 0.14 and 0.41.

The trimethylsilylmethylcelluloses (TMS-MC) produced can be used to produce aqueous gels. In particular, between 10 and 40 percent by weight of TMS-MC are dispersed in water. The solid used is not pretreated or ground in a mill for between 5 and 30 seconds. The solid TMS-MC is dispersed in the water using a laboratory shaker and / or magnetic stir plate and / or Ultra Turrax and / or ultrasonic bath. The dispersion time is between 5 minutes and a day and can, but does not have to be repeated.

The following examples serve to illustrate the present invention.

Synthesis example 1: silylation of methyl cellulose

50 g of the untreated methyl cellulose (viscosity: 1600-1800 mPas) are stirred with 300 g of propylene carbonate. One after the other, 49.7 g of HMDS and 4.72 g of EMImAc are added and rinsed with a further 200 g of propylene carbonate. The reaction mixture is then stirred at 85 ° C. After the reaction mixture has cooled, it is precipitated in 500 ml of ethanol and the solid components are separated off from the liquid components by centrifugation. The solid, gel-like residue is washed several times with an ethanol-water mixture (mass fraction 2: 1) and the mixture is then centrifuged. Finally, the residue is washed with pure ethanol and the product is dried.

Synthesis example 2: silylation of methyl cellulose

25 g of the untreated methyl cellulose (viscosity: 4000 mPas) are stirred with 75 g of propylene carbonate. 83.58 g of HMDS and 8.51 g of EMImAc are added one after the other and rinsed with a further 50 g of propylene carbonate. The reaction mixture is then stirred at 85.degree. After the reaction mixture has cooled, it is precipitated in 500 ml of ethanol and the solid components are separated off from the liquid components by centrifugation. The solid, gel-like residue is washed several times with an ethanol-water mixture (mass fraction 4: 1) and the mixture is then centrifuged. Finally, the residue is washed with pure ethanol and the product is dried.

Synthesis example 3: silylation of methyl cellulose

25 g of the untreated methyl cellulose (viscosity: 15 mPas) are stirred with 75 g of propylene carbonate. One after the other, 41.8 g · HMDS and 8.51 g EMImAc are added and rinsed with a further 75 g propylene carbonate. The reaction mixture is stirred at 85 ° C. After the reaction mixture has cooled, it is precipitated in 500 ml of ethanol and the solid components are separated off from the liquid components by centrifugation. The solid, gel-like residue is washed several times with an ethanol-water mixture (mass fraction 4: 1) and the mixture is then centrifuged. Finally, the residue is washed with pure ethanol and the product is dried.

Example 4: Making a gel of TMS-MC in water

7.5 g of a TMS-MC, ground for 30 seconds and prepared according to Synthesis Example 1, are stirred with 67.5 g of water for one hour on the magnetic stir plate. The mixture is then dispersed on an Ultra Turrax at 10,000 rpm. The resulting gel can be applied to the wooden parts to be glued with a spatula or spoon.

Example 5: Making a gel of TMS-MC in water

15 g of a non-ground, coarsely comminuted TMS-MC prepared according to Synthesis Example 3 are stirred with 60 g of water on a laboratory shaker. The resulting gel can be applied to the wooden parts to be glued with a spatula or spoon.

According to DIN EN 204 and 205, the TMS-MC gels achieve adhesive strengths that almost come close to common adhesives that meet the norm of load group D2 of these DIN regulations. The effect of these silylated methyl celluloses therefore exceeds that of pure methyl cellulose, since it is very susceptible to water after drying and no longer has any adhesive strength after 3 hours in water. Pure methyl cellulose dissolves in water, the glued wooden parts separate from each other again. One advantage is that the use of adhesive strength enhancers, e.g. in wallpaper paste, can be reduced. The biggest advantage is that the use of adhesive force boosters also enables them to be used as an adhesive for wooden components. This means that these building materials can be used with an ecologically harmless, water-based adhesive system. In general, a technical application for non-load-bearing wooden parts is possible.

Claims (10)

Use of silylated alkyl celluloses as an adhesive. Use after Claim 1 , characterized in that the degree of substitution of the alkyl groups (DS _alkyl ) is between 0.5 and 2.5, preferably between 1.0 and 2.2, particularly preferably between 1.6 and 1.8. Use according to one of the preceding claims, characterized in that the degree of substitution of the silyl groups (DS _silyl ) is between 0.01 and 2.5, preferably between 0.1 and 0.5, particularly preferably between 0.14 and 0.41. Use according to one of the preceding claims, characterized in that the alkyl groups are selected from the group consisting of linear or branched alkyl groups with 1 to 18 carbon atoms, in particular methyl. Use according to one of the preceding claims, characterized in that the silyl groups are selected from the group consisting of radicals of the following formula I:

where the radicals R ¹ , R ² and R ^{3 are} each independently selected from the group consisting of C ₁ -C ₃₀ -alkyl, C ₂ -C ₃₀ -alkenyl, C ₂ -C ₃₀ -alkynyl, C ₃ -C ₁₂ -Cycloalkyl, C ₅ -C ₂ -cycloalkenyl or aryl, it being possible for these six radicals to be optionally substituted. Use according to the preceding claim, characterized in that the radicals R ¹ , R ² and R ^{3 are} each methyl. Use according to one of the preceding claims, characterized in that the silylated alkyl cellulose is present as an aqueous gel. Use according to the preceding claim, characterized in that the content of the silylated alkyl cellulose in the gel is between 1 and 80% by weight, preferably between 5 and 60% by weight, particularly preferably between 10 and 40% by weight. Use according to one of the two preceding claims, characterized in that the viscosity of the aqueous gel is from 0.5 to 150 Pa · s, preferably from 1 to 100 Pa · s, particularly preferably from 10 to 75 Pa · s. Use after one of the Claims 7 to 9 , characterized in that the aqueous gel contains at least one further additive selected from the group consisting of hydroxyalkyl celluloses.