WO1993010172A1

WO1993010172A1 - Thermosetting plastic and cellulose fibres composition

Info

Publication number: WO1993010172A1
Application number: PCT/NL1992/000206
Authority: WO
Inventors: Bryan Cecil Smith; Imco Goudswaard; Henri Dominique Joseph Chanzy; Noël Louis CARTIER
Original assignee: Dsm N.V.
Priority date: 1991-11-18
Filing date: 1992-11-17
Publication date: 1993-05-27
Also published as: NL9101920A

Abstract

Composition based on a thermosetting resin and cellulose fibres, whereby the cellulose fibres consist of microfibrils with a length/diameter ratio (aspect ratio) of at least 50, a length of at least 0.5 νm and a crystallinity of at least 60 %, which fibres comprise large crystalline zones. Compounds according to the invention can be used to produce objects for applications in for example the automotive, aerospace, telematics and acoustics industries, in interiors, sanitary equipment etc.

Description

THERMOSETTING PLASTIC AND CELLULOSE FIBRES COMPOSITION.

The invention relates to a composition based on a thermosetting resin and cellulose fibres. Such a composition is known from EP-A-200.409, which describes how certain types of cellulose fibres of bacterial origin can be isolated and used for all kinds of applications, for example as reinforcement in thermosetting resins. The disadvantage of the composition described in

EP-A-200.409 is that the reinforcement of the thermosetting resin by the cellulose fibres is not optimum.

It is the aim of the present invention to provide composition that does not show the aforementioned disadvantage or shows it to a lesser extent.

This is achieved according to the invention in tha the cellulose fibres consist of microfibrils with a length/diameter ratio (aspect ratio) of at least 50, a length of at least 0.5 μm and a crystallinity of at least 60%, which comprise large crystalline zones.

Preferably, the microfibrils have a length/diameter ratio of between 75 and 3000 and a length of between 1 μm and 200 μm, more preferably a ratio of between 100 and 1000 and a length of between 5 and 100 μm. The microfibrils may be of any suitable origin, for example animal, vegetable or synthetic; preferably they are of an animal or a vegetable origin.

Examples of sources of microfibrils are shellfish such as tunicata and plants such as flax, hemp, sisal, wood, valonia, ramie, cotton or jute.

Microfibrils with a diameter of 10-20 nm with a high crystallinity can be isolated from the aforementioned tunicata shellfish. Preferably, the microfibrils consist of one or more large crystalline zones and have an overall crystallinity of at least 80%.

Cellulose microfibrils are described in EP-A- 120.471, but there the microfibrils are used to prepare a gel for use in foodstuffs or cosmetics.

The use of cellulose microfibrils as fibrous reinforcing material has been described by A. Boldizar, C. Klason and J. Kubat in 'Prehydrolized Cellulose as Reinforcing Filler for Thermoplastics', Intern. J. Polymeric Mater., 1987, Vol. 11, pp. 229-262, but this article mentions only the reinforcement of thermoplastics with relatively short microfibrils. The length/diameter ratio is between 5 and 30. This article suggests that the addition of cellulose microfibrils does not have a very favourable effect on the mechanical properties of a product.

The use of cellulose microfibrils as fibrous reinforcing material has also been described by C. Klason in 'Cellulose in Polymeric Compositions', Composite Systems from Natural and Synthetic Polymers, edited by L. Salmen, Elsevier Science Publishers BV, Amsterdam, 1986, p. 65 ff. However, the said article only mentions the combination of cellulose microfibrils with thermoplastics. The article mentions prehydrolized cellulose (bleached pine sulphate) with a length/diameter ratio of more than 100, but with a submicron length. The article characterises microfibrils as a promising material but does not present a solution to the problems involved in the production and processing of such fibrils, such as gelling or breaking of fibres.

The reinforcing effect of microfibrils has been theoretically described and predicted by P. Zadorecki and A. Michell in 'Future prospects for Wood Cellulose as Reinforcement in Organic Polymer Composites' in Polymer Composites, April 1989, Vol. 10, No. 2, but they do not describe the desired aspect ratio nor the desired crystallinity. Nor does Zadorecki indicate how the fibres and the material can be combined or how the fibres can be isolated.

The use of cellulose microfibrils as fibrous reinforcing material is also mentioned in WO-A-8912107, but the described cellulose is of microbial origin and consists of a gel-like mass of intertwined, curled, branched ribbons of poorly crystalline microbial cellulose fibrils because a agent is added to the nutrient bath, which agent interferes with the crystallization of the cellulose.

The use of cellulose fibres as reinforcing materia in thermosetting compositions is also described in EP-A- 260.183, but this patent publication does not mention the use of cellulose microfibrils. The composition according to the present invention can be obtained by subjecting a cellulose source to a treatment comprising of removing the non-crystalline material, dispersing the crystalline material to obtain microfibrils and suspending the microfibrils to prevent coagulation.

X-ray diffraction and electron microscopy data have shown that the cellulose fibrils obtained according to the invention are long straight fibrils, containing almost perfect crystalline zones, the zones having a width of approximately 15 n and lengths of several hundred nanometers.

Powder diffraction data show that the crystallinity of bacterial cellulose is much lower than the crystallinity of the cellulose fibrils made according to the present invention.

The invention hence also relates to a process for the preparation of a composition containing a thermosetting resin and cellulose microfibrils wherein a) a material containing cellulose fibres and optionally residual material is decomposed to fibrils and the residual material is removed; b) the fibrils are dispersed in a solvent and stabilised; c) the solvent is optionally entirely or partially removed; d) the fibrils are combined with the thermosetting resin to obtain a compound. The residual material can be removed by rinsing with a sodium hydroxide solution and/or bleach. The dispersing is preferably carried out in a homogeniser. A homogeniser is an apparatus that is used to homogenise compositions with the aid of high pressures. An example of such a homogeniser is the Gaulin Laboratory Homogeniser, from APV Gaulin International S.A. at Hilversum, the Netherlands.

The suspension of the microfibrils and hence the stabilisation can be effected via the addition of an acid. The acid may be for example H₂S0₄ or HC1.

According to a first preferred embodiment the microfibrils are mixed with a thermosetting resin, by dispersing them in a diluted solution of the resin, for example in water.

The aforementioned article by Klason suggests impregnating the fibres with a polymer solution to prevent breakage of the fibres. However, because this article only discusses the impregnation with a thermoplastic resin, it cannot be concluded that the said impregnation is also possible with thermosetting resins.

The advantage of said process according to the present invention is that the microfibrils are more homogeneously distributed throughout the composition and that less fibre breakage will occur than in the case of a mixing method involving for example compounding in an extruder. A disadvantage of said process according to the invention is that the amount of fibres in the product to be obtained is relatively small. An additional disadvantage is that all the solvent has to be evaporated. The solvent can be removed through filtration, evaporation and/or freeze drying.

Every time the word 'solvent' is mentioned in the present text, this is understood to mean 'solvent mixture' too.

According to a second preferred embodiment the microfibrils are mixed with the resin by first processing the fibres to obtain a flat body, for example a plate or a fleece, and then impregnating this flat body with a thin liquid resin, either in the molten state or in solution. If only a small amount of resin can be applied in one impregnation treatment, the treatment can be repeated once or several times. According to a third preferred embodiment the fibres and the resin are mixed in a ratio between 5:1 and 1:5, preferably around 1:1, in a diluted solution, which is then evaporated by means of spray drying. The result of this treatment is a powder consisting of thermosetting resin and cellulose fibres in the aforementioned ratio.

The product obtained according to the first or second embodiment described above can be ground to obtain a powder consisting at least of microfibrils and an uncured resin. It may be necessary to first dry the product completely or partially before grinding it. The obtained powder has the advantages that it can easily be stored, transported and processed.

It is also possible to mix the fibres and the resin in all manners known to a person skilled in the art, for example by mixing the fibres into a resin of low viscosity to obtain a paste.

The thermosetting resin can be chosen from all possible resins that can be used in compounds. Examples are unsaturated polyesters, epoxy resins, acrylate resins, urethanes, aminoplastics and vinyl-ester resins. Preferably, the resin is chosen from the group consisting of unsaturated polyesters, aminoplastics and epoxy resins. The aminoplastic is preferably a melamine-formaldehyde, a urea formaldehyde or a phenol formaldehyde or a mixture thereof. The resin may also contain all possible additives, such as co-reacting monomers or solvents.

If necessary the resin may contain initiators and/or catalysts, in an amount known to a person skilled in the art. It is possible to modify the surface of the fibres to realise a better adhesion between the fibres and the resin material. This can be done for example by treating the fiber with isocyanates or via other methods known to a person skilled in the art.

A fibre-reinforced resin composition according to the invention can also be defined as a compound. Such a compound can be obtained in the form of a so-called sheet moulding compound (SMC), a dough moulding compound (DMC) , a bulk moulding compound (BMC), a melamine-foππaldehyde compound (MFC), the described powdery composition or any other form of fibre-reinforced resin composition. Compounds normally known in the art comprise glass fibers as reinforcing material.

The composition can be thickened according to a method known to a person skilled in the art.

The compound may further contain the usual additives, for example pigments, fillers such as calcium carbonate, aluminium trihydroxide or cellulose, initiators, accelerators, inhibitors, mould-release agents, other reinforcing agents, etc.

Other fibrous reinforcing agents may be chosen from the group comprising for example cellulose fibres, glass fibres, carbon fibres, mineral fibres such as rock wool, aramide fibres, metal fibres, other natural fibres, for example of cotton, jute, sisal, flax or wood, synthetic fibres such as polyethylene fibres or polyester fibres, other microfibres such as microcarbon fibres, or combinations hereof.

The other fibres may be used in any way in which fibrous reinforcement is usually added to a resin, for example as loose fibres, as long, short or endless fibres, as a mat,^" a fleece, a woven, knitted or braided fabric or otherwise, randomly arranged or specially oriented.

The composition preferably consists of 99-20 vol.% (relative to the overall composition) thermosetting resin, 1-80 vol.% (relative to the overall composition) fibrous reinforcement, consisting of 5-100 vol.% microfibrils, and 0-75 vol.% filler. - More preferably, the composition contains 0.5-60 vol.% (relative to the composition) microfibrils; most preferably 1-50 vol.%.

The compound according to the invention can be processed according to any method for processing compounds known to a person skilled in the art. In general, compounds are processed by allowing them to cure in a particular shap under pressure, at an elevated temperature.

Other possible processing methods are for example injection moulding, compression moulding or reaction injection moulding (RIM).

Compounds according to the invention can be used t produce objects for applications in for example the automotive, aerospace, telecommunication and acoustics industries, in interiors, sanitary equipment, etc. The invention will be further elucidated by the following examples, without being limited thereto. The electron microscopy and the electron diffraction analysis were carried out using a Philips EM 400R Transmission Electron Microscope, at 120 KV, using a reduced beam. The sample holder was cooled with liquid N₂. The flexural strength was determined according to the three-point bending test according to ASTM D790M using a Zwick series type 400 apparatus and specimens with a width of 10 mm and a specimen length that was 20 times the thickness and a bending length that was 16 times the thickness.

The tensile strength was determined using a Zwick series type 1400 apparatus using a specimen with a width of 20 mm, a bending length of 90 mm, a free stretching length of 40 mm and a strain measurement length of 20 mm at 1% πin. The bending test was carried out according to ASTM D790M.

The impact resistance was determined according to ISO standard 179, 'Plastics - Determination of Charpy impact strength of rigid materials' using unnotched bars of 10x4x80 mm; the distance between the supports was 40 mm.

Example I

Isolation of microfibrils

35 g of dried tunicata shells was immersed in 500 ml of a 5% (w/v) aqueous KOH solution and left there overnight at room temperature. The shells were then washed and bleached for 6 hours at 80°C using a mixture of a chlorite solution and an acetate buffer, which was replaced by a fresh mixture every two hours.

This overall treatment was repeated 3 times, after which the shells were completely white.

Then the shells were disintegrated in water with the aid of a Waring blender, after which the suspension obtained was diluted to a concentration of 1% (w/v) and was homogenised in a GAULIN 15 M BTA laboratory homogeniser. The result was a dispersion of microfibrillated cellulose.

300 ml of concentrated sulphuric acid (95%) was added to 450 ml of this dispersion containing 1% cellulose and the mixture was heated to 80°C for 30 minutes to obtain cellulose microcrystals through hydrolysis.

The mixture was filtered using a glass filter with a Dl porosity to separate coagulated cellulose.

The microfibrils and the suspension were then collected through filtration using a glass filter with a D4 porosity and were then rinsed with diluted sodium hydroxide and distilled water. The microfibrils were dispersed in water once again and were subjected to a treatment in an ultrasone bath for 2 minutes using a Bronson B12 Sonifier. The result was an 0.7% (w/v) suspension of cellulose microfibrils in water. The microfibrils had diameters of between 10 and 20 nm and lengths of different μm. The length/diameter ratio was above 100 on average.

The microfibrils comprise large monocrystalline zones or whiskers, as appeared from e.g. dark-field electron microscopy. This showed that the straight microfibrils consisted of single crystalline zones with lengths of at least several dozen nm. The crystalline domains were probably longer but they were not observable with this method because they lay slightly out of the plane (and hence outside Bragg refraction conditions). This was confirmed by means of X-ray diffraction. The elements will be called MFC.

Example II

Preparation of a compound

An amount of 200 ml of the 0.7% (w/v) suspension of example I was filtered and the filtrate was dried to obtain a feltlike sheet with a diameter of 9 cm.

A 55% melamine-formaldehyde solution (MF) was prepared by dissolving 611 g of spray-dried melamine- formaldehyde powder in 500 ml of distilled water at 80°C. --- The feltlike sheet was impregnated with the MF solution by immersing it in a bath. The impregnated sheet was freeze-dried to obtain a compound.

The procedure was repeated using different amounts of MF solution so that sheets were obtained with cellulose contents of a) 26, b) 48 and c) 78 vol.%.

Example III

Processing of a compound

A number of compounds of example II were stacked and compressed at 140°C and 50 bar for 40 minutes, after which they were cooled.

Test specimens were sawn from the plate thus obtained. Under an electron microscope the compressed compound was found to have a very compact structure.

The mechanical properties of the test specimens were determined. The results are shown in Table 1. Example IV

Isolation of microfibrils without homogenisation and processing to a compound

The procedure of example I was repeated without the homogenisation step using the Gaulin Homogeniser. The MFC obtained was processed to a compound according to the process of example II and the compound was processed according to example III.

The mechanical properties shown in Table 1 were determined for the test specimens obtained.

Example V The processes of examples I, II and III were repeated but without the H₂S0₄ and the ultrasonic treatments. The composites were hence compressed immediately after the treatment with the Gaulin Homogeniser.

The mechanical properties of the test specimens were determined. The results are shown in Table 1.

Comparative experiment A Paper

The processes of examples II and III were repeated using a sheet of cellulose-based paper instead of the feltlike sheet. The paper was decor paper (PWA, Germany) of

85 g/m².

The results are shown in Table 1.

Example VI

The specimens as in a) example III and b) example V were ground before the compressing and were then compressed under the same conditions as in example III. The mechanical properties are shown in Table 1. This experiment shows that it is possible to process the material according to the invention via an injection-moulding technique. The results of this example are very reasonable compared with the results of the examples in which these materials were used without the additional grinding step. T A B L E

Mechanical properties

Nr. Cellulose Thick- Flexural Exten- Flexural Thick- Tensile Exten- Tensile type % ness strength sion modulus ness strength sion modulus

10 (mm) (MPa) (%) (GPa) (mm) (MPa) (%) (GPa)

Ilia MFC 26 0.40 132 1.01 13.1 b MFC 48 1.07 215 1.26 17.8 c MFC 78

15

IV* MFC 50 1.05 196 1.27 16.7 v_** MFC 49 1.15 226 1.67 14.5

A paper 48 1.09 195 1.94 10.7 1.10 94 0.96 11.7

20

Via (III) 48 0.98 101 0.85 12.3 b (V) 49 1.02 141 1.07 13.7

25 * without homogenisation

** without H₂ S0₄ and ultrasonic treatments

From Table 1 it can be concluded that a composition containing about 40 vol.% microfibrils has better mechanical properties than compositions with much smaller or much larger microfibril contents (compare example Illb with Ilia and IIIc) .

It can furthermore be concluded that the tensile strength and flexural strength of a compound containing microfibrils are greater than those of a compound with an approximately equal vol.% paper (compare example Illb with comparative experiment A) and that compounds with much smaller or much larger microfibril contents even have a higher modulus than compounds containing paper (compare examples Ilia and IIIc with comparative experiment A).

It can also be concluded that homogenisation has a positive effect on the strength of the compound (compare example Illb with example IV) .

Comparative experiment B

Glass-fibre reinforced compounds and fibre-reinforced compounds

The results of example Illb according to the invention were compared with the results of some measurements of an SMC based on 25% glass fibres and unsaturated polyesters and an MFC (melamine-formaldehyde compound) based on MF and 30% glass fibres and a BMC based on 15% untreated cellulose (flax).

The flexural modulus of the compound according to the invention is about 50% higher than that of SMC, while the flexural strength is about 50% higher than that of MFC. All of the measured mechanical properties are better than those of the compound containing flax.

Furthermore, cellulose fibres present an advantage in terms of weight with respect to glass fibres.

Claims

C L I M S

1. Composition based on a thermosetting resin and cellulose fibres, characterised in that the cellulose fibres consist of microfibrils with a length/diameter ratio (aspect ratio) of at least 50, a length of at least 0.5 μm and a crystallinity of at least 60%, which fibres comprise large crystalline zones.

2. Composition according to claim 1, characterised in that the microfibrils have a length/diameter ratio between 75 and 3000 and a length between 1 μm and 200 μm.

3. Composition according to claim 2, characterised in that the microfibrils have a length/diameter ratio between

100 and 1000 and a length between 5 and 100 μm.

4. Composition according to any one of claims 1-3, characterised in that the microfibrils comprise crystalline zones and the fibres have a crystallinity of at least 80%.

5. Composition according to any one of claims 1-4, characterised in that the fibres are of animal or vegetable origin.

6. Composition according to any one of claims 1-5, characterised in that the thermosetting resin is chosen from the group consisting of unsaturated polyesters, aminoplastics and epoxy resins.

7. Composition according to any one of claims 1-6, characterised in that it consists of 99-20 vol.% (relative to the overall composition) thermosetting resin, 1-80 vol.% (relative to the overall composition) fibrous reinforcing material, consisting of 5-100 vol.% microfibrils and 0-75% additives.

8. Composition according to claim 7, characterised in that it contains between 0.5 and 60 vol.% (relative to the overall composition) microfibrils.

9. Composition according to claim 8, characterised in that it contains between 1 and 30 vol.% (relative to the overall composition) microfibrils.

10. Process for the preparation of a composition containing a thermosetting resin and cellulose microfibrils, characterised in that a) a material containing cellulose fibres and optionally residual material is decomposed to fibrils and the residual material is removed; b) the fibrils are dispersed in a solvent and stabilised; c) the solvent is optionally completely or partially removed? d) the fibrils are combined with the thermosetting resin to obtain a compound.

11. Process according to claim 10, characterised in that the residual material is removed by rinsing it with a sodium hydroxide solution and/or bleach.

12. Process according to any one of claims 10-11, characterised in that the fibrils are stabilised with an acid.

13. Process according to any one of claims 10-12, characterised in that the fibrils are dispersed with a homogeniser.

14. Process according to any one of claims 10-13, characterised in that the solvent is removed through filtration, evaporation and/or freeze-drying.

15. Process according to any one of claims 10-14, characterised in that the fibrils are combined with a thermosetting resin, in a weight ratio between 5 : 1 and 1 : 5, in a solvent, after which the solvent is removed by spray-drying the entire mixture.

16. Process according to any one of claims 10-14, characterised in that the fibrils are combined with the thermosetting resin by processing the fibrils to a flat body and then impregnating this body once or several times with the resin.

17. Process according to any one of claims 10-16, characterised in that the product obtained is ground to a powder.

18. Powder, paste or plate consisting of at least thermosetting resin and cellulose fibres, having a composition according to any one of claims 1-9 and/or obtained using a process according to any one of claims 10-17.

19. Object obtained by allowing a composition or a powder, paste or plate according to claim 18 to set under pressure, at elevated temperature.

20. Composition, process and/or object as entirely or partly described in the specification and/or the examples.