WO2014080086A1

WO2014080086A1 - Novel uses of hemicellulose derivatives

Info

Publication number: WO2014080086A1
Application number: PCT/FI2013/051099
Authority: WO
Inventors: Christiane Laine; Soili Peltonen; Sari HYVÄRINEN; Eva-Lena Hult; Riku Talja
Original assignee: Teknologian Tutkimuskeskus Vtt
Priority date: 2012-11-22
Filing date: 2013-11-22
Publication date: 2014-05-30

Abstract

Use of hemicellulose derivatives as adhesives, or adhesion promoting components, in hot melt or pressure-sensitive adhesives as well as novel adhesive compositions. The present derivatives are preferably ethers or esters of xylan or galactoglucomannan, such as hydroxyalkylated xylan or galactoglucomannan, having a degree of substitution of about 0.15 to 1.5. The molecular weight of the xylan extracted from bleached hardwood pulp or galactoglucomannan extracted from wood chips or meal is suitable as such, and simple derivatization for example by hydroxypropylation delivers a suitable adhesive component.

Description

Novel uses of hemicellulose derivatives

Background of Invention Field of Invention

The present invention relates to adhesive compositions. In particular, the present invention concerns the use of hemicelluloses derivatives as adhesives and to novel adhesive compositions suitable as hot melt and pressure sensitive adhesives.

Related Art

Development of materials from natural polymers for different applications has been of great interest for several years due to increasing prices of petrochemicals and increasing environmental concerns.

Starch-derived chemicals have been developed for decades but recently attention has been drawn to their conflicting demand as also part of the food supply chain. Therefore, nonfood polysaccharides abundantly present in nature, such as cellulose and hemicelluloses, have great potential for material applications.

Chemical derivatives of cellulose, such as cellulose ethers and cellulose esters are extensively used in a great variety of applications for example within the paper and cardboard and pulping industry. Methylcellulose and sodium carboxymethyl cellulose are applied in food science and in many non-food products for example as thickeners, lubricants and adhesives.

One particular field where alternative sources are sought are in hot melt and pressure- sensitive adhesive compositions. Hot melt adhesives are used, e.g., in the bookbinding, packaging and textile industries. The pressure-sensitive adhesives are used in labelling applications of food, household, pharmaceutical and industrial products. Hot melt adhesives and pressure-sensitive adhesives (in the following also abbreviated "PSA") can be described as follows: - Hot melt adhesives comprise a main constituent comprising or consisting of a thermoplastic polymer, optionally blended with additional components, such as modifiers, extenders and inert fillers. When applied upon a surface or into an interface they give rise to a solid structure that is load-bearing at temperatures at which the treated surface or interface is being used (operational temperature or service temperature). The hot melt adhesives melt and form mobile liquids at a higher application temperature.

- Pressure-sensitive adhesives are adhesives that are capable of being applied as dispersions, solutions or hot melts and that are converted to give rise to a rubbery, tacky film of relatively low adhesive strength and rather higher cohesive strength at service temperature.

Typically, pressure-sensitive adhesives can be used to produce bonds that are permanent, but not creep resistant. Importantly, they can also be employed for giving rise to temporary or serial temporary bonds. PSAs are frequently used supported on flexible substrates.

With regard to hot melt and pressure-sensitive adhesives, reference is made to Cope B. C. (2005) Adhesive classification. Recently, degraded cellulose esters have also been used for developing hot melt adhesives. Such compositions contain a cellulose ester component which has been transglycoly sated or oxidized to cleave its anhydroglucose chain. Further the composition contains plasticizers or softeners, such as triethyl citrate, to produce easily melting and flowable mixtures that adhere onto paperboard and cellulose films. With regard to the known art, we refer to WO2009106687A1.

Hot melt adhesives based on cellulose acetate may, in addition to the cellulose acetate component which provides cohesive strength and a softener, also contain low molar mass components working as diluents, for regulating viscosity and tack.

Cellulose esters based on non-food materials are principally interesting components for hot melt adhesives. However, the cellulose molecules are typically so long that they need to be degraded before the cellulose derivatives exhibit sufficient softness for use in hot melts. Such degradation steps will add to complexity of modification. It is an aim of the present invention to eliminate at least some of the problems of the art and to provide novel materials which are useful for various adhesive applications. The present invention is based on the finding that hemicellulose derivatives are useful in adhesives and as adhesion promoting components.

Hemicelluloses are the second most abundant plant material in nature. The global annual growth of wood and other bio raw materials provide annual maximum availability of hemicellulosic raw materials of around 35-70 billion tons, thus representing practically unlimited resources. Xylans are the main hemicelluloses in hardwood. Other important components are the galactoglucomannans which are present in softwoods next to arabinoxylan. Hemicelluloses have been reported for use as additives in papermaking e.g. as such or modified for barrier applications, food additives, thickeners, hydrogel, emulsifiers, coating color component and as cancer protective agents.

In the present invention use of hemicellulose derivatives as adhesives, or adhesion promoting components in hot melt or pressure-sensitive adhesives are provided for.

Preferably, the hemicellulose derivatives are derivatives of xylan or galactoglucomannan or combination thereof. The derivative is typically an ether, ester or a combination thereof. Based on this, it is possible to provide adhesive compositions, consisting essentially of the hemicellulose derivative as such or in mixture with at least one second component selected from the group of

- cohesive compounds, and

- softeners (plasticizer).

More specifically, the present use is characterized by what is stated in the characterizing part of claim 1. The present adhesive compositions are characterized by what is stated in the characterized part of claim 17.

Considerable advantages are obtained by the present invention. Thus, hemicellulose derivatives exemplified in the below examples by xylan or galactoglucomannan ethers exhibit excellent properties as components of hot melt adhesives. For example

hydroxypropylated xylan or galactoglucomannan in mixture with other components, such as oxidized cellulose acetate and a softener such as triethyl citrate or other plasticizers, are therefore potential components for pressure sensitive hot melt adhesives. The present adhesives, when tested on commercial board materials, have given a reversible tacky seam on the board after heat activation under pressure.

As the below discussed results show, compounded samples of the present materials can be processed at moderate temperatures, in the range of 100 to 150 °C.

The advantage of this hot-melt adhesive is that the molecular weight of the xylan extracted from bleached hardwood pulp or wood chips, and that of glucomannan and xylan extracted from bleached softwood pulp or wood chips, respectively, is suitable as such, and simple derivatization for example by hydroxypropylation delivers a suitable adhesive component while e.g. the molecular weight of cellulose or starch has to be adjusted in addition to derivatization.

It should be pointed out that hemicelluloses and in particular xylan can be produced from different kinds of wood or agro-based materials using different kind of uncomplicated and inexpensive extraction methods. Extraction of the xylan from wood and agro-based material can be performed rather easily in alkaline conditions after lignin removal.

Bleaching before the extraction is optional depending on the desired properties, e.g.

whiteness. Alkaline extraction and purification of white and pure xylan from hardwood pulps, like bleached birch kraft pulp, enables the production of high adsorption and high crystalline pulp. The same is possible of softwood as well, to give a mixture of xylan and galactoglucomannan. Also hot water extraction of both, softwood and hardwood, delivers a sidestream that contains hemicelluloses.

Next embodiments of the present technology will be discussed in more detail. Brief Description of the Drawings

Figure 1 shows the opening of tacky glue seams of glued board and packaging paper samples from adhesive mix 5 (coded mix 7 in the picture).

Figure 2 shows the testing arrangement for debonding tests of a glued folding boxboard specimen.

Figure 3 presents the glass transition temperature and maximum debonding load for the adhesive joint for some examples of adhesive formulations. Description of Embodiments

In the following description, embodiments of the invention are disclosed with particular reference to xylan. However, it should be understood that the description is equally applicable to other hemicellulose species, in particular to other hemicelluloses, such as glucomannans and galactoglucomannans. The preferred hemicelluloses are derived from wood and tree, in particular from species of deciduous trees. They can be isolated for example by alkaline extraction directly from the wood itself (e.g. from wood chips) or from cellulosic or lignocellulosic pulp prepared from the wood raw material. Also other plant materials than wood can be used as a source of the hemicelluloses.

As explained above, the present invention provides for the use hemicellulose derivatives as adhesives, or adhesion promoting components, in hot melt or pressure-sensitive adhesives.

An adhesive composition can therefore be formulated such that it consists essentially of the hemicellulose derivative as such or preferably in mixture with at least one second component. The at least one second components is typically selected from the group of compounds contributing to cohesion (cohesive compounds), and softeners.

The cohesive compound is present in a concentration of up to 50 % by weight.

The hemicellulose derivative forms about 1 to 99 % of the total weight of the composition, typically it forms about 10 to 85, preferably about 20 to 75 % of the total weight of the composition. In a preferred embodiment it is used with cohesive components, forming jointly up to 75 % of the total weight, in particular about 25 to 70 of the total weight of the composition.

The hemicellulose derivative is a derivative of xylan or galactoglucomannan or

glucomannan. In particular the derivative is a chemical derivative of hemicelluloses, in particular of the said hemicelluloses.

Preferred derivatives include ethers, esters and combinations thereof. Hydroxyalkylated derivatives (hemicellulose ethers) are particularly preferred wherein the alkyl chain comprises 1 to 6 carbon atoms, ethyl, propyl and butyl being particularly preferred.

Optionally the alkyl chain contains substitutent(s), such as hydroxyl groups. The ester groups can be derived from Ci to C₂₄, in particular Ci to C₂o carboxylic acids and combinations thereof, for example Ci to C₆ or Ci₂ to C₂o or combinations thereof. The latter expression includes combinations of lower alkanoic acid and fatty acid esters.

Ethers can be produced by reacting the hemicelluloses or etherified (e.g. hydroxyalkylated) hemicellulose derivative with the corresponding alkylene oxide, such as ethylene oxide or propylene oxide. Esterification can be carried out in an analogous fashion as for starch, described in detail in U.S. Patents Nos. 6,369,215 and 6,605,715.

According to a preferred embodiment, the hemicellulose is esterified with a short chain aliphatic carboxylic acid or reactive derivative thereof. Typically the carboxylic acid has 1 to 10 carbon atoms, and in particular it has the formula

CH₃(CH₂)„COOH wherein n is an integer 0 to 4.

One particularly preferred embodiment comprises acetylation of the starting material. In such a process, the alkali used for isolating hemicellulose from a plant raw-material can be employed as a catalyst for the acetylation reaction, which removes the need for separate purification of the raw-material. The derivatization, in particular chemical derivatization, will confer properties of thermoplasticity. In all of the above mentioned derivatives, the degree of substitution of the hemicelluloses derivative is 0.1 to 3, for example 0.2 to 2.5, in particular 0.15 to 1.5, naturally depending on the hemicelluloses.

The average molecular weight M_w of the hemicellulose is, preferably also after derivatiz- ation, 2 000 to 200 000, for example 3 000 to 100 000, in particular 3 000 to 40 000 Da. Molecular weights in the range of about 3 000 to 35 000 are particularly interesting since they combine good mechanical properties with softness of the material.

Specific examples of the above hemicellulose derivatives, in particular etherified hemicelluloses derivatives, include the following: hydroxyalkylated xylan or

galactoglucomannan, in particular hydroxypropylated xylan or galactoglucomannan.

Specific examples of hemicellulose esterified ether derivatives include esters of hydroxyalkylated xylan or galactoglucomannan, in particular a C₂ to C₂o, preferably a C₂ to C₆ ester thereof.

The thermoplasticized hemicellulose-based composition can be a hemicellulose ether or esterified ether in mixture with a plasticizer or a cohesive compound or mixtures thereof. The hydroxyalkylated hemicellulose or hemicellulose ester is plasticized by admixing it with a softener or plasticizer known as such. Therefore, the thermoplastic composition is advantageously made to contain 0.01 to 95% by weight, advantageously about 1 to 50%> by weight and preferably about 10 to 40% by weight of a plasticizer. Any known plasticizers can be used, examples thereof including the following: triacetin, diacetin, monoacetin, triethyl citrate, tributyl citrate, acetyl triethyl citrate, acetyl tributyl citrate, dimethyl succinate, diethyl succinate, ethyl lactate, methyl lactate, fatty acid esters of glycerol, castor oil, olive oil, rapeseed oil, pine oil, waxes dibutyl phthalate, diethyl phthalate, and mixtures thereof. In preferred embodiments, the softener is selected from the group of triethyl citrate, triacetin, and glycerol and combinations thereof. Preferably, the softener is present in a concentration of up to 60 % by weight.

The adhesives can be in the form of dry powder or as dispersions.

In the case of dry powder a mixture of the hemicellulose derivative with the softener is generally sufficient. However the hemicellulose compositions may, in both cases, contain other additives and auxiliaries known as such within the field of polymer and plastics technology, such as lubricators, antistatic agents, colorants, pigments, fire retardants and reinforcing and filling agents. These additives and auxiliaries are present in an amount of about 1 to 95 % of the weight of the composition, typically 10 to 50 %. As regards the auxiliaries, particularly the following may be mentioned: waxes (e.g. alkylketene dimer wax (AKD) or beeswax, cf. below), reinforcing agents (see below) and fillers, such as titanium dioxide, calcium carbonate, kaolin, aluminium hydroxide, sodium silicoaluminate, barium sulphate and zinc oxide. The preparation of the dry powder can be carried out by heating the hemicelluloses derivative to achieve softening and then the softener along with any additives and auxiliaries can be mixed in and dissolved into the hemicellulose derivative.

The solid adhesive formulation are typically prepared by providing a hemicellulose derivative premixed with a cohesive compound and a plasticizer into a preheated compounder and by processing the mixture for a predetermined time. Typically, a melt is produced. The time is generally about 1 to 120 minutes, in particular about 10 to 30 minutes. The temperature is selected depending on the melting or softening point of the hemicelluloses derivative. A temperature in the range of about 50 to 220 °C, in particular about 75 to 200 °C, for example about 80 to 200 °C, or 90 to 175 °C, is normally suitable.

Dispersions can be formulated from the hemicellulose derivatives. In order to prepare such a dispersion, the hemicellulose derivative is added to water by the aid of a dispersion auxiliary, whereby the plasticized polymer melt can be dispersed in water in sufficiently fine particles in order to form a stable dispersion. Examples of dispersion auxiliaries include polyvinyl alcohol (PVA), particularly PVA having a weight-average molar mass of approximately 10,000 to 115,000. Other dispersion auxiliaries (protective colloids) include cationic starch and hydroxyalkyl starch which may be used separately or together with PVA. Furthermore, as additives or auxiliaries, the dispersions may contain alkylketene dimer (AKD) wax and beeswax.

According to an embodiment the present dispersion compositions are prepared by dispersing the plasticized hemicellulose derivative melt in water using auxiliaries. In order to achieve plasticizing the derivative is admixed with a plasticizer preferably at an elevated temperature in order to form a melt. On a small scale the plasticization can be carried out in e.g. a flask equipped with a reflux condenser and having efficient agitation. The temperature varies depending on the plasticizer used but is typically about 50 to 250 °C, preferably about 100 to 200 °C. On a larger scale, plasticization is advantageously performed in a melt-processing apparatus, such as an extruder.

Preferably, the dispersion comprises a dispersing agent. Advantageously the dispersing agent is selected from the group of copolymers based on ethylene oxide and propylene oxide and polyvinylalcohol and combinations thereof.

The plasticized melt is dispersed in a liquid phase, usually water, using said auxiliaries. Water is considered a particularly advantageous dispersion medium according to the invention but the invention can also be applied to various kinds of solvents. The hemicellulose is preferably a xylan or galactoglucomannan derived from wood or agricultural sources, in particular alkali-extracted xylan from hardwood kraft pulp, such as birch pulp, in particular bleached birch or Eucalypt kraft pulp, optionally bleached, or galactoglucomannan extracted from softwood or softwood pulp, optionally bleached. The adhesive composition may contain a cohesive compound. Generally, such a component improves internal cohesion of the adhesive bond. Typical components are polymeric materials, including fibrous materials. The cohesive polymers preferably have a rather high glass transition point so as to avoid softening of the bond at increased temperatures. In particular glass transition points in the range from 140 °C and higher are preferred.

In one embodiment, the cohesive compound of the adhesive composition is formed by a starch or cellulose derivative, polylactide or poly(lactic acid) (PLA) or polyhydroxy- alkanoates (PHA) and mixtures thereof.

In a preferred embodiment, the cohesive compound is formed by as a cellulose or starch ester or a mixture thereof, for example cellulose or starch acetate or mixtures of cellulose or starch acetates, in particular a cellulose or starch acetate having a DS of 0.5 to 2.5. Particularly preferred are cellulose or starch derivatives the molecular weight (M_w) of which is in the range of 4 000 to 500 000, for example 6 000 to 200 000, in particular 10 000- 100 000 Da. Depending on the intended use, a hemicellulose derivative formulation of the above kind can therefore be made to contain 0.01 to 30% by weight, preferably about 5 to 30% by weight of a cellulose ester, such as cellulose acetate, cellulose propionate or cellulose butyrate, or mixed esters thereof. Based on the above, the dispersions contain typically water as a dispersion medium and hemicelluloses derivatives as dispersed phase. The hemicelluloses derivatives may be mixed with cohesive components and even with plasticizers. For improving dispersion some auxiliary solvent, such as a ketone (e.g. acetone) can be employed. Generally, the solid matter content of the dispersion is about 1 to 25 % by weight, in particular about 5 to 20 % by weight, for example about 10 to 15 % by weight. The proportions of the components of the solid matter are as defined above - thus, typically, the solid matter contains hemicellulose derivative(s) at 1 to 99 parts by weight, in particular about 10 to 85 parts by weight, preferably about 20 to 75 parts by weight; it contains cohesive compound at 1 to 75 parts by weight, in particular 5 up to 50 parts by weight; and it contains 0 to 50 parts by weight of plasticizer, in particular 0 to 40 parts by weight. In addition there can be about 0.1 up to 20 parts by weight of other non- volatile components present in the dispersion. Next a specific embodiment of preparing xylan and galactoglucomannan derivatives suitable for adhesives, as well as of the adhesives as such, will be discussed in more detail.

It should be noted that the specific details are also applicable to other hemicelluloses.

Preparation of xylan

A production process for pure and essentially linear xylan has been developed and upscaled. The process includes alkaline extraction of bleached birch pulp and purification by e.g. ultrafiltration, precipitation or a combination of the methods (cf. Laine, C. et al, "Hydroxyalkylated xylans - their synthesis and application in coatings of packaging and paper", the content of which is herewith incorporated by reference.

The xylan extract can be a very pure xylan (i.e. free from other hemicellulose components) with only 1-2 % of the total sugars are other than xylose.

After extraction, the xylan can be isolated by precipitation or ultrafiltration techniques.

The xylan thus obtained from bleached birch kraft pulp has a low solubility and alkaline conditions have to be applied to dissolve it. Once dried, this xylan becomes hardly soluble even in strong alkaline due to the deacetylation of xylan in pulping and bleaching.

Xylan production can be scaled up to obtain several kg of xylan using alkaline extraction followed by ultrafiltration with membranes of a nominal cut-off of, e.g., 5 000 or 10 000 Da.

Next to bleached birch kraft pulp, pulps from other hardwood species can be used as xylan source. Also unbleached hardwood pulps are potential raw materials as well as pulps from other pulping processes than the kraft process.

Galactoglucomannan can be isolated e.g. by pressured hot water extraction (PHWE) and by precipitation from the extract (cf. Krogell J. et al., "Intensification of hemicellulose hot- water extraction from spruce wood in a batch extractor - Effects of wood particle size") Modification of xylan and galactoglucomannan

Xylan and galactoglucomannan can be modified to their ethers using propylene oxide or glycidyl ether reagents. The modifications can be performed for e.g. isolated non-dried xylan or in a so-called reactive extraction.

Hydroxypropylation is shown in Scheme 1 for xylan.

Scheme 1

Derivatization of xylan in the extraction phase without previous separation from the pulp dispersion - the so-called 'reactive extraction' - is an attractive alternative to save tedious and expensive intermediate separation and concentration steps. Another major benefit of the process is the enhanced reactivity of the xylan in the extraction liquor without intermediate separation and especially drying.

This technique can be applied to produce hydroxypropylated xylan.

Xylan and galactoglucomannan based adhesives Hydroxypropylated xylan synthesized from xylan extracted from birch kraft pulp is a thermoplastic polymer. Typically, the molar mass of the hydroxypropyl xylan is on the same level as the starting xylan, with a slight increase possible due to hydroxypropylation. Correspondingly, galactoglucomannan can be hydroxypropylated. The xylan's or galactoglucomannan's degree of substitution with hydro xypropyl is typically in the range of about 0.1 to 3, in particular abour 0.2 to 1.5, in particular about 0.3 to 1.0, e.g. 0.5, determined by ¹³C-NMR.

For adhesive application the substitution should be sufficiently high to give an internally plasticized polymer that has thermoplastic properties.

To give an example, when xylan is hydroxypropylated to give a DS of 0.5, the glass transition temperature of the modified xylan decreases to 76 °C from 171 °C of the pure xylan extracted from birch kraft pulp. The thermal degradation property of such hydroxyl- propylated xylan, when showed that compounding can be carried out at 100-150 °C which is far from the modified xylan's degradation temperature (Tio_%) of 265 °C. The modified xylan or galactoglucomannan can be blended at elevated temperature for example in the compounder with additional components, such as oxidized cellulose acetate (CA ox) and triethyl citrate (TEC). Typically, the weight portions of the various components are 1 to 30 parts by weight of cellulose derivative, 10 to 60 parts by weight of hemicellulose derivative and balance softener along with other components, making 100 parts by weight in total.

The components can be compounded to produce a tacky blend in a melted form. The tackiness remains in the blend after cooling down. This hot melt adhesive formulation based on modified xylan or galactoglucomannan reinforced with CA ox was spread and molten between two card boards by heat activation under pressure. The card boards adhered well to each other. The adhesion was tested by tearing slowly and fast the card boards by hand. The slow tearing test showed tacky seam and no fiber damages was observed whereas the fast tearing resulted in fiber rupture.

In one embodiment, the present adhesives are used at temperatures of roughly 50 to 150 °C.

The following non-limiting examples are presented by way of illustration. Examples

Materials and methods

Hydroxypropylated xylans (HPX) and galactoglucomannan (HPGGM) as well as acetylated HPX were prepared according to common procedures (Jain et al. 2001).

The conditions and chemical dosages are shown in Table 2. After the reaction, pH was adjusted to neutral pH with H₂SO₄ and then the product was purified with ultrafiltration (cut off 3000 or 5000 Da).

Hydroxypropylated xylan HPX 2 was hexanoated as following: 25.0 g HPX 2 and 23.7 mL pyridine were dissolved in 350 mL dimethylacetamide and the mixture was stirred overnight. 57.5 mL hexanoic anhydride was added slowly during 30 minutes and the reaction mixture was heated under stirring at 70 °C for 19 hours. The reaction mixture was poured into 1.2 L deionized water and filtered. The residue was redispersed into 600 mL ethanol for several days forming a gelly mixture and poured into a 4-fold amount of water. This was repeated three times and the final solid product was dried in a cvacuum oven yielding 26.3 g of the product HPX 2 hexanoate.

Cellulose acetate (CA) from Coulthard with high degree of substitution (DS) was oxidized using hydrogen peroxide with 10 w-% charge of H₂0₂ according to Mikkonen et al. (2011) as reported earlier.

Table 1. Reaction parameters in the hydroxypropylations; the reactions were carried out in pressured 5 L Biichi reactor equipped with mixer

NMR analysis

1H and ¹³C NMR experiments were carried out at 25°C on a Bruker Avance III 500 MHz instrument equipped with a z-gradient double-resonance probe. NMR samples were prepared by dissolving approximately 20 mg of hydroxypropylated xylan in 0.7 ml d₆- DMSO. The solvent signal was used as an internal chemical shift reference point (5m 2.5

Quantitative ¹³C NMR spectra were acquired with inverse-gated decoupling pulse sequence, 3 s pulse delays, 4096 scans and chromium(III)acetylacetonate (0.15M) for complete relaxation of all nuclei. For the HSQC NMR experiments, the spectral widths were 5000 Hz and 20 000 Hz for the 1H- and ¹³C- dimensions. The number of transients used was 32 with 256 time increments always on the ¹³C- dimension. The 'Jc_HUsed was 145 Hz. Data processing was performed using standard Bruker Topspin-NMR software.

Molar mass distributions (MMD's)

MMD's of cellulose acetate samples were calculated from size exclusion (SEC) measurements using PL MiniMixA columns in DMAc/=.8% LiCl with RI detection and pullulan (5 900 - 1 600 000 g/mol) calibration. MMD's of modified xylan and

galactoglucomannans were calculated from size exclusion (SEC) measurements performed using MCX columns in 0.1M NaOH with RI detection and pullulan (5 900 - 708 000 g/mol) calibration. The samples were dissolved in 1M NaOH.

TGA

Thermal analysis of xylan and galactoglucomannan derivatives were performed using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) with Seiko Instruments TGA/DTA 320. The apparatus was continually flushed with argon (100 mL/min). The measurements were done in the range 25-650 °C, with a heating rate of 10 °C/min.

DSC (Determination of glass transition point)

The DSC measurements were performed using conventional DSC instruments. For hydroxypropylated samples, equilibration was performed at 25 °C, then first heating was performed to 120 °C followed by cooling down to -50 °C. Second and third heating was performed to 205 °C with cooling cycles to -50°C. Heating and cooling rates were 10°C /min. For the cellulose acetate samples, the same program was used with the exception that the second and third heating cycles were performed up to 255 °C.

Compounding

The different components were compounded at 100-150°C with a micro-compounder of DACA instrument (Tables 3-5).

Gluing trials

The compounded samples were placed between the board or paper samples and placed into the preheated oven under a marble plate. The samples were cooled down at least 30 min before testing. Testing

The glued samples were torn by hand and by debonding tests. Results

Alkali-extracted xylan and hot water extracted galactoglucomannan were

hydroxypropylated to different degree of substitution. Esterification to acetate and hexanoate was performed for selected HPX's. Information about the samples is collected in Table 2. The hemicellulose derivatives were used in glue compounding. Table 2. Sample list and analysis results

HP = hydroxypropyl group; Ac = Acetyl group; Hex = hexanoyl group; * by capillary electrophorese determination after hydrolysis; ^Alower transition, but no actual glass transition; #HPX A was prepared correspondingly to HPX 1 and 2 from xylan alkali- extracted from bleached birch kraft pulp.

Compounding of solid adhesive formulations

The adhesive mixtures at a 5-7 g scale were prepared at 100-150°C by adding the premixed compounds into the preheated micro-compounder (DACA instruments) rotating at 100 rpm for the announced time. The mixtures could be prepared in the compounder. They melted or softened in the equipment. Thus, the compounding of mixtures of oxidized cellulose acetate,

hydroxypropylated xylan or galactoglucomannan and different softeners yielded homogenous samples, while the compounding of only hydroxypropylated xylan and triethyl citrate was unsuccessful.

Tables 3-5 show compositions and compounding conditions of tested hot melt adhesive formulations (check table numbers!)

Table 3. Examples of adhesive formulations blended at 150

Mix 1 Mix 2

CA ox 20% 20%

HPX A 35%

HPX A acetate 35%

Triethylcitrate (TEC) (softener), 45% 45%

commercial

T °C 150 150

t, min 40 40 min

Remark Melted in the compounder. Good mixing, possible to

To be taken out by opening take out as a slightly the equipment. Tacky after drawable cord, low torque cooling down. throughout compounding (2

Nm)

Table 4. Various examples of adhesive formulations comprising hydroxypropylated xylan originating from bleached birch kraft pulp

* Mix 3-5 were also successfully prepared using triacetin as softener instead of triethyl citrate using only 10 minutes compounding time. In addition, Mix 4 was prepared successfully using glycerol instead of triethyl citrate.

Table 5. Examples of adhesive formulations comprising hydroxypropylated hemicelluloses originating from Eucalypt pulp or pine wood

Preparation of dispersed adhesive formulation

2.02 g of freeze-dried xylan hexanoate comparable to HPX 2 hexanoate and 0.20 g of Polyvinyl alcohol (PVOH40-88) were weighed into a round bottom glass followed by heating up to 160 °C. The temperature was increased further up to 160 °C prior to the melting of the powdery mixture. The mixture was cooled down to 90 °C followed by addition of aqueous solution of Pluronic F123 (20 g; 1.5 % solids). The addition was carried out slowly with simultaneously mixing. A few milliliters of acetone were added to the solution and mixing was continued while the solution cooled down to room

temperature. A diluted dispersion was obtained during evaporation of most of the acetone leaving traces of acetone in the final dispersion

Gluing tests with solid hot melt adhesive formulations

Gluing was performed on commercial folding box board with a grammage of -200 g/m² and commercial brown packaging paper.

The mix 1-8 were tested in preliminary tests resulting in tacky glue seams. There were some differences in the tackiness and softness that related to the degree of substitution or the softener used. Selected test results are shown in Table 6 .Mix 5 containing HPX with the highest degree of substitution was clearly softer than mix 3 and 4. Mix 6 with a lower proportion of softener was also softer but was not distributing so well on the paper.

The following test conditions were applied:

- Compounded mixtures were placed between two small board pieces with a spatula after softening in a glass bottle at 80-100 °C

- both board pieces either coated or uncoated on the contact to the glue

- 10 min at 100- 120 °C under pressure

- Tacky seam on slow tearing

Table 6

Mix 3 Mix 4 Mix 4 Mix 4

(TEC) (glycerol) (glycerol) Mix 5

Blending temperature 120°C 120°C 120°C 100°C 120°C softer, less

Remark tacky tacky hard hard brownish

Gluing at 120 °C, 10 min under pressure

strong strong coated-cotaed board strong tack tack fiber tear fiber tear tack softer softer softer tack tack than tack than than with with with glossy-glossy packaging paper board board fiber tear fiber tear board An example of a sample is shown in Figure 1.

Debonding tests with solid hot melt adhesive formulations Selected adhesive formulations compounded at 120 °C with triethyl citrate (TEC) or triacetin (TA) as plasticizer were used as an adhesive between two commercial folding box board stripes (width 25 mm). The hot melt adhesive was placed at one end of the pigment coated side of the stripe. On the top of this construction, the other stripe was placed against the hotmelt adhesive with the uncoated side. The gluing was finalized in an oven under 2 kg weight at 120 °C for 10 min. The t-shaped test specimens were successfully glued by the hot melt formulations of the present study.

The obtained t-shaped sample was tested using a tensile testing machine (Texture analyzer, TA XT plus). The ends of the sample were clamped in the cross-head grips of the tensile testing machine. Figure 2 shows the experimental set up of the 180° de-bonding test. The lines describe the card board stripes that have been glued together and attached to the clamps. The arrow shows the direction of the crossliead.

A load of a constant cross-head speed (1.67 mm/s) was applied and the maximum de- bonding load was recorded. The de-bonding load of the specimens varied from 1.26 to 4.65 N. No fiber tear were observed in the test of the glued specimen after one day storage. This shows that de-bonding mechanism is controlled by adhesive failure rather than cohesive failure. However, after storage of the specimen for 3 months fiber tear for the Mix 3 TEC, Mix4_TEC, Mix6_TEC, Mix7_TA and Mix8_TA was observed.

Neither the degree of substitution in hydroxypropylation nor the hemicellulose source affected significantly the Tg value recorded for the formulations. The Tg was more controlled by the Tg of the plasticizer used based on the Tg of the pure TEC and TA which are -75 and -72 °C, respectively.

The glass transition temperature (Tg) were measured for the compounded formulations showing values well below room temperature ; Figure 3 gives the maximum debonding load for adhesive joint and glass transition temperature of the hotmelt formulation. Sample codes are explained in the text. TEC - triethylcitrate, TA - triacetin. Testing of dispersed adhesive formulation

1) The product was tested as glue on paper. The glue line spread on the paper was tacky. Paper with the glue was adhered on a painted vertical surface on which the paper remained. 2) The dispersion was spread on commercial release paper prior to evaporation of the solvent (water and acetone). A tacky adhesive layer was formed to which paper was attached. The paper with the adhesive layer could be peeled from the release paper exposing tacky adhesive ready to be attached. The paper was adhered on a painted vertical surface on which the paper remained.

Industrial Applicability

The present derivatives can be used generally as adhesives, or adhesion promoting components, in various applications. Thus, one field of use is as adhesives in packages in particular in fibrous packages, such as cardboard packages, for example in the food and in the pharmaceutical industry as well as for other consumer products. Due to good adhesive properties they can be used for providing tamper-proof packages. As noted above, adhesives, such as hot melt adhesives, can also be used, e.g., in the bookbinding and in the textile industries.

Another interesting field of application is as pressure-sensitive adhesives. Areas for such labelling applications can be found in food, household, pharmaceutical and industrial products. A third promising field of application are fugitive glues, i.e. glues which are low-tack adhesives that will give re removable, non-permanent joint. Small if any damage will be cause to the surfaces after separation of the glue.

Adhesives are considered to be removable, if they can be peeled cleanly from a test substrate without causing any damage to the test substrate. Thus, typically, based on a peel test (180 peel test (N/25 mm), the following characterizations can be made of adhesives:

Excellent permanent >14

Permanent 10 - 14 Semi-removable 2 - 4

Excellent removable <1

The present adhesives have interesting applications in particular as semi-removable and excellently removable adhesives. The fugative glues fall in these two categories.

References

Patent literature

WO2009106687A1

US Patent Specification No. 6,369,215

US Patent Specification No. 6,605,715 Non-patent literature

Cope B. C. (2005) "Adhesive classification", in Handbook of Adhesion, Ed. D. E.

Packham, John Wiley & Sons, Ltd, Chichester, UK, pp. 25-28. Jain, R. K., Sjostedt, M., Glasser, W. G. (2001) "Thermoplastic xylan derivatives with propylene oxide", Cellulose 7: pp. 319-336.

Krogell, J., Korotkova, E., Eranen, K. Pranovich, A, Salmi, T., Murzin, D., Willfor, S., (2013) Intensification of hemicellulose hot-water extraction from spruce wood in a batch extractor - Effects of wood particle size, Bioresource Technology 143 (2013) 212-220

Laine, C, Harlin, A., Hartman, J., Hyvarinen, S., Kammiovirta, K., Krogerus, B., Pajari, H., Rautkoski, H., Setala, H., Sievanen, J., Uotila, J., Vaha-Nissi, M. (2013),

"Hydroxyalkylated xylans - their synthesis and application in coatings of packaging and paper", Industrial Crops and Products 44, 692-704. http://dx.doi.Org/10.1016/j.indcrop.2012.08.033.

Claims

1. Use of hemicellulose derivatives as adhesives, or adhesion promoting components in hot melt or pressure-sensitive adhesives.

2. The use according to claim 1, wherein the hemicellulose derivative is a derivative of xylan or galactoglucomannan.

3. The use according to claim 1 or 2, wherein the hemicellulose derivative is an ether, ester or a combination thereof.

4. The use according to claim 3, wherein the degree of substitution is 0.1 to 3, in particular 0.15 to 2.0, for example 0.15 to 1.5.

5. The use according to any of the preceding claims, wherein the average molecular weight M_w of the hemicellulose is 3 000 to 200 000, for example 3 000 to 100 000, in particular 3 000- 30 000 Da.

6. The use according to any of the preceding claims, wherein the hemicellulose derivate is hydroxyalkylated xylan or galactoglucomannan, in particular hydroxypropylated xylan or galactoglucomannan.

7. The use according to any of the preceding claims, wherein the hemicellulose derivative is an ester of hydroxyalkylated xylan or galactoglucomannan, in particular a C₂ to C₂o, preferably a C₂ to C₆ ester thereof.

8. The use according to any of the preceding claims, wherein the hemicellulose is a xylan or galactoglucomannan derived from wood or agricultural sources, in particular alkali- extracted xylan from hardwood pulp, such as bleached birch or Eucalypt kraft pulp or galactoglucomannan extracted from softwood.

9. The use according to any of the preceding claims, wherein the hot melt or pressure- sensitive adhesives comprises a composition consisting essentially of the hemicellulose derivative as such or in mixture with at least one second component selected from the group of

- cohesive compounds, and

- softeners.

10. The use according to claim 9, wherein the cohesive compound is formed by a starch or cellulose derivative, polylactide or poly(lactic acid) (PLA) or polyhydroxyalkanoates (PHA) and mixtures thereof.

11. The use according to claim 9 or 10, wherein the cohesive compound is formed by a cellulose or starch ester or a mixture thereof, for example cellulose or starch acetate or mixtures of cellulose or starch acetates, in particular a cellulose or starch acetate having a DS of 0.5 to 2.5.

12. The use according to claim 11, wherein the M_w of the cellulose or starch derivative is in the range of 4 000 to 500 000, for example 6 000 to 200 000, in particular 10 000- 100 000 Da.

13. The use according to any of claims 9 to 12, wherein the cohesive compound is present in a concentration of up to 50 % by weight.

14. The use according to any of claims 9 to 13, wherein the softener is selected from the group of triethyl citrate, triacetin and glycerol and combinations thereof.

15. The use according to any of claims 9 to 14, wherein the softener is present in a concentration of up to 60 % by weight.

16. The use according to any of claims 10 to 15, wherein the hemicellulose derivative is present in a concentration of at least 10 % by weight, in particular 15 to 100 % by weight.

17. An adhesive composition, consisting essentially of the hemicellulose derivative in mixture with at least one second component selected from the group of

- cohesive compounds, and

- softeners.

18. The adhesive composition according to claim 17, which is provided in dry form or as a dispersion.

19. The adhesive composition according to claim 18, wherein the dispersion comprises a liquid medium selected from aqueous and non-aqueous media, in particular water or a polar liquid.

20. The adhesive composition according to any of claims 17 to 19, wherein the cohesive compound is a cellulose or starch derivative, polylactide or poly(lactic acid) (PLA) and polyhydroxyalkanoates (PHA) and mixtures thereof.

21. The adhesive composition according to any of claims 17 to 20, wherein the cohesive compound is a cellulose or starch ester or a mixture thereof, for example cellulose or starch acetate or mixtures of cellulose or starch acetates, in particular a cellulose or starch acetate having a DS of 0.5 to 2.5, or a mixture thereof.

22. The adhesive composition according to claim 20 or 21, wherein the M_w of the cellulose or starch derivative is 4 000 to 500 000, for example 6 000 to 200 000, in particular 10 000 - 50 000 Da.

23. The adhesive composition according to any of claims 17 to 22, wherein the softener is selected from the group of triethyl citrate, triacetin and glycerol and combinations thereof.

24. The adhesive composition according to any of claims 18 to 23, wherein the dispersion comprises a dispersing agent, preferably the dispersing agent is selected from the group of copolymers based on ethylene oxide and propylene oxide and polyvinylalcohol and combinations thereof.