WO2003035573A1

WO2003035573A1 - Hybrid fibre composite precursor

Info

Publication number: WO2003035573A1
Application number: PCT/GB2002/004825
Authority: WO
Inventors: Dutiro Cuthbert
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-10-23
Filing date: 2002-10-23
Publication date: 2003-05-01
Anticipated expiration: 2004-04-23
Also published as: EP1497242A1; GB0125368D0

Abstract

Natural organic fibres can be mass treated to produce a hybrid construction material with improved surface water permeability, improved fire resistance, improved early flexural strength, and which can be used as a reinforcing material for cement or concrete by mass mixing in a polymer organic self-curing precursor/sodium silicate solution, followed by mass treatment with a mineral acid/salt solution and then contacted with an aluminium containing solution or paste.

Description

HYBRID FIBRE COMPOSITE PRECURSOR

The present invention relates to a building material, which is based on modified natural fibres precursor mass treated to make them more suitable for use in manufacturing mass products for construction and building.

It is also known to use natural fibres as a filler in concrete, however the concrete will attack and degrade natural fibres and make them unsuitable for such use.

It is also known to use inorganic compound 'treated' organic natural fibres in cement to make organic natural fibre cement however water permeates through the surface of such products or dampens them and makes them sag to become mechanically weaker and unsuitable for external cladding and waterproofing.

It is also known to include polymers in fibrous cement during manufacturing to produce macro-defect free ement, which has improved water resistance but in the highlighted processes this results in clogging up of the mixing machinery and loss of polymer additive during the process.

In many parts of the world, supplies of organic natural fibrous materials are available either as a natural organic material or as a waste product or by-product of other processes, such as cotton lint waste, waste from wood pulp manufacture, etc. and I have now devised a method of mass treating organic natural fibrous products to enable them to be used as an improved reinforcing material and as a strength gain accelerator, a binding or processing aid product in fibre cement manufacture.

According to the invention there is provided a method of mass treating pumped organic fibrous material which method comprises (i) contacting the organic fibrous material dispersion with a mixture of the polymer precursor (adduct, semi-cured, oxidizing or reducing) and sodium silicate and (ii) contacting the treated material with an acid to deposit polymer precursor-silicate hybrid, an polymer precursor-silicic acid or polymer precursor- polysilic acid on the fibrous material and then (iii) contacting the treated fibrous material with an aluminium oxide containing compound. The sodium silicate is preferably a neutral or alkaline solution e.g. of the type commonly known as water glass. The stoichiometric composition for a neutral composition of sodium silicate is a SiO₂:Na₂O ratio of 3.3:1 and for an alkaline sodium silicate a SiO₂:Na₂O ratio of <3.3: 1. A typical alkaline grade sodium silicate has a SiO₂: Na₂O ratio of 2: 1.

The organic polymer precursor can take the form of any liquid two part or one part 'self- curing polymeric species, e.g. acetic acid/acetic anhydride or epoxy based adducts, polyvinyl or acetate, acrylic acrylate, polyurethane based or alkyd resin based preferred. The quantity of polymer precursor to silicate solution is 1 : 10.

Preferably a solution of sodium silicate is used in which the viscosity of the solution is low enough to enable the sodium silicate solution to flow over the fibrous material and to penetrate the fibres. A typical commercially available solid concentration is 40% solids content, which is about 142 g/1 for a neutral grade sodium silicate solution and 99g/l for an alkaline grade sodium silicate, but these concentrations are not critical.

Preferably the fibrous material is mass treated in a water dispersion preferably in a pipe/confined volume as shown in the diagram (Fig 5) as it is pumped through the system to allow enough mixing time and make use of the turbulence in the pipe during transport to allow the organic polymer precursor/silicate solution to interact with all the fibrous material.

The acid used to contact the treated fibrous material is a preferably a mineral acid e.g. sulphuric acid. The pH of the acid should be between 2 and 4 and, for sulphuric acid; an acid solution of about 10 to 30% weight acid is suitable. Preferably the acid solution should be mixed with a salt of the acid to saturate the acid solution and, in the case of sulphuric acid, any salt can be used e.g. sodium sulphate, but the less soluble salts e.g. calcium sulphate are preferred. The preferred concentration of the salt is 10% to 20% weight in the solution. The treatment of the material with the acid/salt solution preferably takes place at 20°C to 100°C, more preferably at 20 °C to 60 °C. In an embodiment of the invention the fibrous material dispersion is continuously pumped and hence mixed with the organic polymer/sodium silicate solution, earlier in the process (Fig 2) and the acid /salt solution introduced at a later stage (Fig 3) at a rate automatically matched by an ordinary/electronically operated dispenser (Fig.4) with the organo-silicate hybrid, this is then dewatered (Fig 5) to obtain the treated fibrous material which is subsequently treated with an aluminium compound during the building product making phase. The aluminium compound is preferably a solution or cementitious paste containing alumina or an aluminium salt and any aluminium oxide paste.

The treatment with the aluminium compound is believed to result in the formation of aluminium silicate sites on the fibrous and organic polymer precursor-fibre material. The presence of the alumina silicate sites results in improved fireproofing of the treated organic material and in better matrix bonding properties. The inclusion of the organic polymer precursor believed to be adsorbed as well as ionically and covalently bonded to the organic fibre (as shown in Figure 20) in the treatment process results in the adsorbed polymer being dispersed in the paste to fill out the air voids during mixing, and the ionically and covalently bonded sections.

The dispersion of the treated material in alkalis such as cements and concrete is increased by treatment by the method of the invention. The treated product can be wetted and dried normally with no loss of fire resistance. The coating imparts improved toughness, work of fracture, acoustic absorption, flexural strength and further resistance to insect attack, e.g. from termites, and to fungal or microbial attack to the cementitious composites formed with it.

The dispersed organic polymer precursor is also believed to further react with itself and form a layer on top of the product due to its density and act as a hydrophobic barrier for water penetration. During mass processing of the treated fibre containing paste to produce building products, the organic polymer precursor is attached to the fibre and does not freely flow and disperse away with the water to clog various equipment components.

During curing of the building composites formed the polymer precursor forms a network of poly-organo-inorganic compounds as an additional binder with the cementitious phases to form stronger composites handleable to service strength within 5 days.

It is believed that, in the^' treatment with the organic polymer precursor/sodium silicate, the silicic or polysilicic acids are precipitated in such a manner that they trap parts of the polymer precursor forming particles, which regularly deposit on the natural fibre surface, form into larger conglomerations with a diameter in the nanometer range. The cellulosic chains on the fibre also partially react with the organic polymer precursor on the surface, which might also be containing the silica or silicic acid. Thus a network of organic/inorganic compounds is formed (Figure 19). The majority of the groups are believed to be hydrophobic (e.g. Figure 21), some of the free reactive groups will be hydrophilic and ionic allowing further reaction with cementitious compounds within the pastes used to form the products. The surface of the fibrous material is charged and this charge is neutralised by cations such as Al³⁺, Mg²⁺, Na⁺, Fe²⁺, Ca⁺ ions present in cement. The handling properties of the treated fibrous materials are similar to the untreated material ready to be used for the manufacturing process but have improved resistance to wetting and improved resistance to alkali attack and to insectoidal, fungal or microbial attack.

In a preferred embodiment of the invention a solid polymer precursor-silicate- cellulose product is formed when the multi-component solution (polymer precursor blended silicate alkaline solution and the fibrous substance) is treated with an acid solution containing preferably about 10 to 20 percent by weight of H₂S0 , about 10 to 20 percent by weight of Na₂S0₄ or preferably CaS0₄ at a temperature of 20°C to 100°C, preferably about 20°C to 60°C, for a sufficient time.

An aluminium containing solution is added at the processing stage. The aluminium will react strongly with the surface of the organic polymer precursor/poly-silicic acid hybrid sites if there is enough of it in the solution. The treatment can be carried out with for example, at a temperature of 0°C to 100°C, preferably about 20°C to 60°C, for a sufficient time. During the natural organic pulp fibre treatment process and within the natural organic/pulp fibres the polymer precursor silicate hybrid has been precipitated in such a manner that its primary particles, regularly distributed on the cellulose fibre backbone, form into larger agglomerations with a diameter measurable in nanometers which can be seen on SEM micrographs or other optical-microscopic methods (Figure 22).

Other salts/oxides of Al can be used for the modification, in which case the aqueous solution made from them with the aluminium in a suitably reactive form is used in the same manner as the aluminate solution.

The natural fibrous materials which can be treated by the method of the invention include softwood/hardwood fibres after pulping, as fresh or waste pulp from paper mills, with compositions of 40-45% cellulose, 15-35% hemicellulose, 17-35% lignin as neutral, acid, sulphite, kraft, or mechanical pulps. Cotton or fibrous cotton lint waste with more than 2% impurity of any kind and all naturally occurring organic fibrous materials whose aspect ratio is greater than 500 can also be used. The basic cellulosic backbone and reactive groups as shown in Figures 21. The surface groups on for example waste pulp fibres are mainly carboxylic (- COOH) and sulphonic (-SO₃H) acid groups and their anionic nature gives them an affinity for cationic additives and can also be reacted with reactive groups of the organic polymer precursor. At high pH they are in their dissociated salt form, and at low pH in their undissociated form. Since treatment is done at low pH this allows the organic substance to react with these surface groups, and when the fibre is then mixed in a paste, which is of a high pH, some of the free sites can take part in the normal cementitious reactions.

The untreated fibres are attacked if they are exposed to any form of fungal attack although it is a well proven concept that wood fibres can be mixed in a cement matrix without the risk of microbial attack due to the inaccessibility of such fibres to the microbes, as they are normally fully embedded in the reinforced matrix at fibre volume fractions of less than 9% by volume. The treated fibres are resistant to fungal attack.

The treated fibrous material of the invention can be used as a reinforcing fibre for any suitable binder or construction material matrix such as concrete or cement, mud etc. The materials formed by the method of the invention when mixed with cement gains enough strength to be handled as if in service within 48 hours can also be used as a construction material due to their increased water penetration resistance and biological attack.

The invention is illustrated in the Examples.

Example 1

A total of 1000kg of waste pulp was mass treated by pumping it through a pipe (Figure 5) and contacting it at valve inlet 1 (Figure 2) with an alkaline solution containing 142g/l neutral grade sodium silicate (contained in Figure 10) dispensed with an alkaline/acid resistant electronic injector (Figure 3) at a rate of 5g/s at 25°C.The second acid solution (contained in Figure 9) was injected at the second injection valve (Figure 4) matched with the first injection at lg/s of an acid mixture of 30g/l sulphuric acid/50g/l sodium sulphate solution and 14.2 g/1 of acetic anhydride at 30 °C for 1 hour. The treated fibres were then dried using mechanical squeezer (Figure 7), and bagged (Figure 8) ready for mass production of building products. Sample treated fibres were taken, washed and boiled with water and dried to be used in Examples 2-6.

Example 2

The procedure of example 1 as repeated using epoxy resin adduct based on Shell EPON 825 resin, based on the diglycidyl ether of bisphenol-A: and Texaco Jeffamine D-230 polyoxypropylenediamine (adduct prepared at 30 degrees C for 20 minutes leaving unreacted sites ) instead of the acetic anhydride, this time together with the sodium silicate solution.

Example 3 Fire Resistance

The products of examples 1 and 2 were tested for fire resistance by heating in air at a temperature of 20°C to 1000°C at a rate of 10 degrees a minute for 90 minutes and the results compared with untreated pulp.

The product of Example 1 lost 30 to 44% of its weight below 520°C to 752°C as shown on a TGA curve shown in Figure 11 compared with the untreated material which lost 93% of its weight below 337 °C as shown on a TGA curve shown in Figure 12. The product of Example 2 lost 20-40% of its weight below 478 °C as shown on a TGA curve shown in Figure 13 compared with 93% below 326 °C for untreated material as shown on a TGA curve shown in Figure 14.

In the cementitious composites themselves, the SEM pictures show that hydration crystallisation products in the composites were formed as normal as shown in Figure 15. The untreated fibre, silicate only treated fibre, organic polymer precursor (polyurethane varnish) treated fibre was used to make ten 200mmx200mm composites by compaction at 2Mpa pressure with and 0.4 water to cement ratio, 10% fibre and 90% OPC grade cement these were cured for 5 days.

Example 4 Water Absorption

The samples were first dried at 50 degrees C for a day in vacuum and then a bucket of water (1) as in Figure 16 placed on top of each sample. This was left for 24 hours and the weight change for each sample was recorded on Table 1 together with an observation as to complete water penetration across the thickness (showing dampness on the lower side B) or not.

The samples reinforced with the treated fibre show less than 5% weight gain and no dampness on the lower side B. Samples reinforced with untreated fibre show a 13- 22% weight gain and some dampness on lower side B. SEM pictures taken on the surface of the specimen shown in Figure 17 a flatter surface on the treated fibre reinforced composites and fibroids of cross-linking network of polymer.

Example 5 Early strength gain

The same samples made as for Example 4 were tested for standard 3 point bending flexure on a Testometric machine after 5 days and the graphs shown in Figure 18 were obtained. The samples with treated fibre have a load carrying capacity greater than four times that of silicate treated and untreated fibre and hence exceed service strength during this period.

Example 6 Commercial Scale treatment of Pulp crumble at Art Corporation, Mutare /Pulp Mill, Zimbabwe Samples of STD pulp crumble and pulp crumble treated according to example 1 effluent were taken from effluent facility every two hours and handsheets made in the laboratory.

Tensile, burst and tear tests were carried out and the following results were obtained.

In example 6 for the treated pulp:-

❖ Tensile index improved to 19.3% initially to 91.4% after lOhrs.

❖ Burst index improved by 51.6% stabilized and then increased to 100% after 10 hrs.

❖ Tear index changed by 1.5% initially and improved to 19.3%.

Claims

1. A method of mass treating organic fibrous material which method comprises (i) contacting the organic fibrous material with an organic polymer precursor/sodium silicate mixture and (ii) contacting the treated material with an acid to deposit an organic precursor/silica hybrid, or an organic precursor/silicic acid hybrid or organic precursor/polysilicic acid hybrid on the fibrous material and then (iii) contacting the treated fibrous material with an aluminium compound.

2. A method as claimed in claim 1 in which the acid is sulphuric acid.

3. A method as claimed in claim 2 in which the sulphuric acid is a solution of 10 to 20% weight acid.

4. A method as claimed in claim 1 or 2 in which the acid solution contains a saturated salt solution of the acid

5. A method as claimed in claim 4 in which the salt is sodium sulphate.

6. A method as claimed in any one of the preceding claims in which the fibrous material is mass mixed with a an organic polymer precursor /sodium silicate solution, the fibrous material is then mixed in the acid solution, the fibrous material squeeze dried and dewatered to obtain the mass treated fibrous material which is finally treated with an aluminium containing binder to mass produce building products.

7. A method as claimed in any one of the preceding claims in which the aluminium compound is a solution or cementitious paste containing alumina or an aluminium salt.

8. A method as claimed in any one of the preceding claims in which the natural fibrous material is wood fibres after pulping, or waste pulp from paper mills

9. A method as claimed in any one of the preceding claims in which the natural fibrous material is cotton or fibrous cotton lint waste.

10. A method as claimed in any one of the preceding claims in which the natural fibrous material is naturally occurring organic fibrous material with an aspect ratio of greater than 500.

11. Fibrous organic material treated by the method of any one of the preceding claims.

12. Concrete containing fibrous organic material treated as claimed in any one of the preceding claims.

13. A method as claimed in any one of the preceding claims in which the organic precursor is acetic anhydride/acetic acid, epoxy based adducts, alkyd resin based, polyester, vinyl acetate/acrylate or polyurethane based or any other semi-cured polymeric compound.