Insulating Composite Material and Method of Forming the Insulating Composite

Abstract

The invention provides an insulating composite material that is suitable for formation into insulation products configured to reduce thermal loss in large scale structures. The insulating composite ma

Description

The present invention relates to an insulating composite material and method of manufacture. Particularly though not exclusively, the invention provides a composite material used to form boards or semi-flexible sheets of insulation for use in the construction industry. Conventional insulating material includes rolls of fibreglass for fitment between building joists. This insulation is not self-supporting and is therefore more difficult to handle than solid insulation blocks. In addition, the fibreglass acts as an irritant and installers need to wear protective face masks and gloves in order to safely handle the fibreglass. More recently, self-supporting insulating panels or blocks have been extensively used in the construction industry. These panels are typically made of a layer of closed-cell polymer foam, such as polyisocyanurate or phenolic foams, sandwiched between protective foil sheeting. These panels are easy to handle and cut to shape for installation into cavities or between joists. Another structure in common use is the structural insulated panel (SIP). These laminates comprise wood-based oriented strand boards (OSBs) which sandwich a foam core and are used in erecting external structural or internal partition walls in buildings. Some of these insulating materials are potentially harmful to the environment. In recent years there has been greater demand to use more natural materials to replace the synthetic foams and fibres currently in use. For example, EP2924058 discloses a composite material comprising natural wood fibres, a polyisocyanate binder and silica-based nano porous particles (aerogel). This material is however weak and prone to disintegrate, making handling difficult. The present invention seeks to provide a fibre composite insulation material which is environmentally friendly yet provides adequate insulation performance and is capable of easy handling. According to a first aspect of the invention there is provided an insulating composite material for thermal insulation, the insulating composite material comprising: refined wood fibres, silica-based aerogel particles, a resin binder and microfibrillated cellulose, wherein the refined wood fibres are coated with silica-based aerogel particles and microfibrillated cellulose. The insulating composite material is preferably suitable for formation into insulation products configured to reduce thermal loss in large scale structures. Advantageously, the insulating composite material includes a combination of materials to form a unique composite that provides the required thermal insulation and structural integrity for use as thermal insulation within the construction industry, with reduced environmental impact when compared with conventional insulation products. Preferably, the refined wood fibres have silica-based aerogel particles and microfibrillated cellulose bonded thereto. The resin may act as a bonding agent. The silica-based aerogel and microfibrillated cellulose are preferably randomly dispersed on an exterior of the refined wood fibres. Preferably, the silica-based aerogel particles and microfibrillated cellulose adhere to an exterior of the refined wood fibres. Coating the refined wood fibres with silica-based aerogel particles and microfibrillated cellulose advantageously improves structural integrity of the formed insulating composite material. The refined wood fibres may be pre-processed to select wood fibres that provide optimum performance within the insulating material. For example, the refined wood fibres may be pre-processed wood fibres having at least one of the following properties: a specified range of lengths and / or dimensions, recycled and / or reclaimed fibres; a specified type of wood fibre; and / or separated wood fibres. The refined wood fibres may have a size (length) of about 0.5 mm to about 5.0 mm. The refined wood fibres may have a size (length) of between around 1 mm to about 5 mm. The refined wood fibres may have a size (length) of between around 3 mm to about 5 mm. The refined wood fibres may be soft wood fibres. The refined wood fibres may comprise virgin pine fibres or pine chips. Alternatively, the refined wood fibres may comprise recycled medium density fibreboard (MDF) fibres. The use of recycled MDF fibres provides a further sustainability benefit which is a key incentive for implementation and use of the insulation in the construction industry. The refined wood fibres may be pre-processed to separate individual fibres. Separation of individual wood fibres is advantageous since it prevents ‘clumping’ and aggregation of the wood fibres to enhance even mixing of the constituent parts of the insulating material. The refined wood fibres may be pre-processed to reduce the moisture content of the fibres. The refined wood fibre content may be at least 20 wt%. The refined wood fibre content may be less than 70 wt%. The refined wood fibre content may be around between 50 and 65 wt%. The refined wood fibre content may be around between 55 and 60 wt%. The resin binder may comprise a setting polymeric material. The polymeric material may comprise urea-formaldehyde. The polymeric material may comprise resorcinol formaldehyde adhesive. The polymeric material may comprise polyisocyanate. Other known resin binders may be used. The aerogel content may be in the range between 5 to 40 wt%. The aerogel may comprise at least 6 % of the weight of the insulating composite material. The aerogel content may be in the range of 8 to 30 wt%. The aerogel content may be at least 10wt%. Preferably, the aerogel content may be in the range of 10 to 25 wt%. The aerogel may comprise particles having a largest diameter of less than 5500 microns. The aerogel may comprise comprises particles having a largest diameter of less than 1500 microns. The silica-based aerogel particles may be hydrophilic. The aerogel may comprise hydrophilic aerogel. Optionally, the aerogel may comprise Quartzene® Z1. The insulating composite may comprise micro- crystalline cellulose. The insulating composite may comprise nano- crystalline cellulose. The microfibrillated cellulose (MFC) content may be between around 1 and 10 wt%. The MFC content may be at least 3 wt%. The MFC content may be between around 2 and 6 wt%. The MFC content may be around 5 wt%. Use of MFC in the composite of the invention is advantageous, since the MFC have been found to be capable of stabilising the natural fibre composites of the present invention, providing structural resilience. Microfibrillated cellulose has a high surface area entanglement of fibre strands. It is derived from natural wood, such as spruce. As such it is an ecologically sustainable material. The fibres promote H-bonding and thus, chemical integration into a range of compositions and binders is possible. The insulating composite material may be configured in a preselected form to provide thermal insulation. The insulating composite material may be configured in a preselected form to provide thermal insulation for large scale structures, such as buildings. The insulating composite material may be configured to form thermal insulation having a thickness of at least 2 mm. The insulating composite material may be configured to form thermal insulation having a thickness of 5 mm or more. The insulating composite material may be configured to form thermal insulation having a thickness of 10 mm or more. The insulating composite material may be a building insulating composite material. The building insulating composite material may be formulated for use as large-scale insulation. The insulating composite material may be configured as insulation boarding. The material may be formed into a block or panel for use in construction of buildings. The insulating composite material may be configured to form insulation boarding having a thickness of at least 15 mm. The insulating composite material may be configured to form insulation boarding having a thickness of 20 mm or more. The insulating composite material within the insulation boarding may have a density of at least 100 kg / m3. The insulating composite material within the insulation boarding may have a density in the range between around 115 and 230 kg / m3. The insulating composite material within the insulation boarding may have a density of at least 135 kg / m3. Alternatively, the insulating composite material may be configured as semiflexible or sheet insulation. The insulating composite material may further comprise a bi-component fibres. The bi-component fibre may comprise an inner core and an outer sheath, the outer sheath having a lower melting point compared with the outer sheath. The inner core and the outer sheath may comprise two different materials. The bi-component fibres may be formed from naturally derived materials. The bi-component fibres may be formed from a bio-degradable material. The bi-component fibres may be formed from bio-derived PBS (polybutylene succinate) and / or PLA (polylactic acid). The bi-component fibre content may be between around 10 and 35 wt%. The bi-component fibre content may be between around 15 wt% and 25 wt%. The bi-component fibre content may be between around 15 wt%. The balance may comprise refined wood fibres coated with MFC and aerogel using a resin binder. The insulating composite material may be configured to form semi-flexible or sheet insulation having a thickness of at least 2 mm. The insulating composite material may be configured to form semi-flexible or sheet insulation having a thickness of between around 5 mm and 15 mm. The material may be moulded into any desired shape before setting, and further processed by cutting or incorporating into other structures, such as structural insulated panels (SIPs). According to a second aspect of the invention, there is provided an insulation board comprising the insulating composite material according to the first aspect of the invention. The insulation board may have a thickness of at least 15 mm. The insulation board may have a thickness of 20 mm or more. The insulation board may have a density of between 115 and 230 kg / m3. The insulation board may have a density of at least 135 kg / m3. According to a third aspect of the invention, there is provided semi-flexible or sheet insulation comprising the insulating composite material according to the first aspect of the invention. The sheet insulation may have a thickness of at least 5 mm. The insulating composite material may be configured to form semi-flexible or sheet insulation having a thickness of 10 mm or more. The semi-flexible or sheet insulation may have a density of between 35 kg / m3 and 75 kg / m3. The semi-flexible or sheet insulation may have a density of between 40 kg / m3 and 70 kg / m3. The semi-flexible or sheet insulation may have a density of between 45 kg / m3 and 65 kg / m3. The semi-flexible or sheet insulation may have a density of around 65 kg / m3. According to a fourth aspect of the invention there is provided a method of forming a composite material as hereinbefore described comprising: applying a resin binder to refined wood fibres with a liquid mixture of silica-based hydrophilic aerogel particles and microfibrillated cellulose, in a turbulent flow of fluid to form a base material; reducing the moisture content of the base material; and forming and setting the base material into a composite. Thus, the refined wood fibres within the composite are coated with aerogel particles and microfibrillated cellulose. The method may comprise the step of applying the resin binder and liquid mixture to the wood fibres in a blowline. Advantageously use of the blowline generates a turbulent fluid flow to comprehensively mix the components forming the base material. Use of hydrophilic aerogel particles is advantageous during the manufacture of the insulating material, as the wet mixture is less prone to clumping and clogging flowlines during manufacture. The step of reducing the moisture content of the base material may comprise flash drying the material. The step of reducing the moisture content of the base material may comprise reducing moisture content to less than 15 %. The step of reducing the moisture content of the base material may comprise reducing moisture content to between around 4 and 10 %. The step of forming the base material may comprise pressing the base material. The step of setting the base material into a composite may comprise heating the material. The step of forming and setting the base material into a composite may comprise simultaneously pressing and heating the material. The method may further include the step of altering physical properties of the composite material by altering at least one of the following: depth of press; temperature; and / or speed of the pressing step. Alternatively, the method may further comprise the step of mixing bicomponent fibres into the base material. Mixing bi-component fibres into the base material may include turbulent mixing and / or mechanical mixing. The bicomponent fibre content may be added in a quantity between around 10 and 35 wt% of the overall material. The bi-component fibre content may be around 15 wt%. The balance may comprise the base material of refined wood fibres coated with MFC and aerogel using a resin binder. Turbulent mixing may comprise entraining the fibres of base material and bi-component fibres into an airflow along a tortuous path. The tortuous path may have portions that are aided by gravity and / or opposed by gravity i.e. the tortuous path may have portions with a vertical or inclined element with reference to the ground such that the fibres entrained in the airflow travel substantially up or down portions of the tortuous path. Mechanical mixing may comprise the step of physically urging an even distribution of bi-component fibres within the fibres of the base material. Mechanical mixing may comprise transmittal of the fibres through intermeshing teeth. Advantageously, the mechanical mixing physically blends the fibres to achieve an even distribution. Mechanical mixing may occur in a vertical chamber such that the downward transit of fibres is assisted under gravity. Mechanical mixing may occur in a chamber having a pressure differential such that the fibres are urged through the intermeshing teeth. The step of forming and setting the base material into a composite may comprise laying the required quantity of mixed fibres onto a surface and heating the material to a predetermined temperature to form a sheet of insulation. The required quantity of mixed fibres may be attained by weighing the mixed fibres laid on a surface. The mixed fibres may be laid in a uniform sheet in the required quantity. The bi-component fibre within the fibre mixture may comprise an inner core and an outer sheath having a lower melting point than the inner core. The step of setting the base material into an insulating composite may comprise heating the material to a predetermined temperature between the melting point of the inner core and outer sheath of the bi-component fibres such that the outer sheath of the bi-component fibres melts to bind the composite material into a sheet of insulation. Advantageously, the melted outer sheath binds the material, while the solid inner core holds the fibres in spaced relation giving the material loft and thereby improving the insulation properties. The method may comprise recycling wood fibres. The recycled wood fibres may be obtained from recycled MDF. Alternatively, the method may comprise providing virgin wood fibres. The method may comprise providing wood fibres of a preselected size. The method may comprise refining wood fibres. The method may comprise preselecting wood fibres having a length between around 0.5 to 5.0 mm. The method may comprise preselecting wood fibres having a length between around 0.5 to 3 mm. Alternatively, the method may comprise preselecting wood fibres having a length between around 3 to 5 mm. The method may comprise processing wood fibres to separate the fibres. It may be advantageous to process the fibres to minimise ‘clumping’ and reduce the presence of ‘shives’ (or bunches of fibres). The method may comprise forming an insulating composite material according to the first aspect of the invention. The method may comprise forming insulation board from the insulating composite material according to the second aspect of the invention. The method may comprise forming sheet insulation from the insulating composite material according to the third aspect of the invention. According to a fifth aspect of the invention, there is provided a method of forming an insulating composite material, the method comprising the steps of: mixing wood fibres, particles, microfibrillated cellulose and a bonding agent in a stream of air to form a web of base material; and bonding the base material to form an insulating composite material. The method may comprise air laying or air forming. The bonding step may comprise one or more of the following methods: latex bonding, thermal bonding, and / or high-pressure bonding. High pressure bonding may include hydroentanglement. According to a sixth aspect of the invention, there is provided composite insulation made by method steps according to any of the fourth or fifth aspects of the invention. Each aspect of the invention may be combined with any other feature, embodiment or aspect of the invention described herein, where appropriate. Following is a description, by way of example only and with reference to the figures of the drawings of modes for putting the invention into effect. In the drawings: - Figure 1 is a schematic of a wood fibre with aerogel and MFC nanoparticles bonded and attached thereto; Figure 2 is a photograph of a wood fibre composite boards in accordance with the invention; Figure 3 is a graph showing modulus of elasticity (MOE) of wood fibre composite boards in comparison with density of the wood fibre composite boards; Figure 4 is a graph showing modulus of rupture (MOR) of wood fibre composite boards in comparison with density of the wood fibre composite boards, Figure 5 is a graph showing R value of wood fibre composite boards compared to density of the wood fibre composite boards; Figure 6 is a graph showing R value per metre thickness of wood fibre composite boards compared to density of the wood fibre composite boards; and Figures 7a and 7b are end and perspective schematic views respectively, of a bi-component fibre incorporated into the composite according to another embodiment of the invention. Embodiments of the present invention will now be described with reference to the drawings. The embodiments describe creation of an insulating composite base material, methods for manufacture of an insulating composite material in the form of a board and sheets. According to other examples, additives may be incorporated into the materials or alternative / additional method steps may be used to arrive at the composite and method of manufacture claimed herein. According to a first embodiment of the invention, soft-wood pine chips are refined in order to select the desired length fibres using a refiner and are separated to avoid clumping. The resultant wood fibres have a length of between around 0.5 mm to about 3.0 mm. According to an alternative embodiment described below, the wood fibres may be refined to select a fibre length of between 3 mm and 5 mm. An additive liquid mixture is created using the aerogel, MFC and water. Hydrophilic aerogel particles in the form of Quartzene Z1 and microfibrillated cellulose (MFC) are well mixed and dissolved in the water with a total combined concentration of 130 g / L for both additives. A blowline is used to spray and mix the refined wood fibres with ureaformaldehyde (UF) resin and the liquid aerogel / MFC solution. The turbulent flow of resin, wood fibres and additives in solution cause a thorough wet mix of the base material that provides a uniform dispersion in the final product. The size of the spray nozzles for the blowline and the required pump power are preselected and adjusted according to the required quantities of the base materials and / or speed of manufacture. The wet base material is dried in a flash drier for several seconds to reduce the water content from around 200 % to 7-10%. The resulting dried base material is used to form an insulating composite material. Preparation of the base material as described ensures that individual refined wood fibres are coated with aerogel and MFC particles. Research leading to this invention has shown that the coating of the refined wood fibres in this way provides an insulting composite material with superior structural and thermal properties. The base material may be processed in different ways to produce building insulation in the required form as appropriate for each specific application and end use. Examples provided below describe the process steps leading to formation of insulation boarding using the composite material of the invention, and processing of the base material to form sheets of insulation using an airlaying process. In order to to produce insulation panels, once the process of resin / additive application to the wood fibres and drying is complete, the resulting base material is pre-pressed. This is followed by a consolidation step to form the base material into the required shape and depth in a rectilinear panel mould using a computer controlled hot-press. The forming, pressing and heating steps result in creation of a wood fibre composite in the form of a board, which is partially structural and can support its own weight. Figure 2 shows a photograph of stacked wood fibre composite boards 20 made using the process described. Physical properties of the insulation boards 20 can be altered during the pressing step by adjusting characteristics such as press depth, press speed and temperature. According to an alternative embodiment, a one-step manufacturing process employing a ContiRoll® press may be used as part of a press production line to continually form and shape the base material. At the end of this process the wood fibre composite is cut to the required size. The wood fibre composite resulting from the above described method of manufacture provides an insulating composite that is suitable for use in the construction industry. The schematic figure 1 shows a basic view of how an individual wood fibre 10 might be seen in the finished composite. The wood fibre 10 is coated with a plurality of silica-based aerogel particles 14 which improve thermal properties of the finished composite and bonded with MFC particles 12, which improve structural integrity. Experiments were conducted investigating different variables associated with manufacture of the wood fibre composite insulation board. In all cases, hot pressing was performed at 180 °C and boards were pressed to a thickness of 25 mm. Table 1, ‘Batch description’, shows the different aerogel I MFC concentrations (as well as pressing time for batches 1 and 2) and the nominal density of each batch in kg / m3. Table 1 Batch description Batch Size (m2) Pressing time (min) Aerogel concentration (%) MFC concentration (%) Nominal density (kg / m3) 1 1 5 0 0 92.8 2 1 6 0 0 96 3 1 7 0 0 112 4 1 7 5 0 120 5 1 7 5 0 140 6 1 7 5 0 180 7 1 7 10 0 120 8 1 7 10 0 180 9 0.5 7 5 0 256 10 1 7 0 0 120 11 1 7 0 0 140 12 1 7 0 0 180 13 1 7 5 5 120 14 1 7 5 5 140 15 1 7 5 5 180 Following manufacture, the boards were rated on appearance and handling as well as general formation. Initial observations and densities of the boards are shown in Table 2 below. Board integrity was assessed based on the ability of the whole board to withstand manipulation without breaking or otherwise disintegrating. A positive value (Y) indicates that the board could be handled, whereas a negative result (X) indicates lack of suitability of that board for use in a commercial process. Table 2. Physical attributes of boards Batch Nominal density (kg / m3) Board integrity Measured Thickness (mm) Actual density (kg / m3) 1 92.8 X 24.5 111.37 2 96 X 24 127.7 3 112 Y 23.9 150.01 4 120 X 23.75 121.54 5 140 Y 23.6 139.35 6 180 Y 23.6 158.73 7 120 X 22.9 136.81 8 180 Y 24.3 167.41 9 256 Y 23.72 247.84 10 120 X 24.1 203.02 11 140 X 24.03 202.81 12 180 Y 24.1 222.5 13 120 Y 22.75 160.11 14 140 Y 23.1 177.28 15 180 y 23.1 229.28 The results show that at the lowest board densities, there was difficulty in manipulation of the boards. It is clear that density control varied form the nominal, which may be explained by the fine control of the press at such low densities. This is also the explanation for the final thickness of the boards measuring less than the nominal 25 mm in all cases. It is likely that there would be less deviation from the expected norms when these boards are produced in a uniform factory process, rather than a laboratory setting. The results also showed that the addition of MFC increased the handling strength of the boards as well as the density. Where possible sub samples were tested for indicators of mechanical strength including modulus of rupture (MOR) and modulus of elasticity (MOE). Results are shown in Table 3 below. It was not possible to test boards marked with an ‘x’ from Table 2, since these test samples would not support their own weight (and are listed as ND in Table 3). Table 3 - MOE and MOR values (with standard deviation) of insulation board samples. Batch MOE (MPa) MOR (MPa) 1 ND ND 2 ND ND 3 8.86 ±3.52 0.08 ± 0.03 4 ND ND 5 5.26 ± 2.99 0.05 ± 0.02 6 13.04 ± 1.05 0.11 ±0.01 7 ND ND 8 4.39 ± 1.14 0.06 ±0.01 9 61.53 ± 10.62 0.4 ± 0.08 10 ND ND 11 ND ND 12 17.63 ± 13.20 0.12 ±0.07 13 10.24 ± 5.11 0.11 ±0.04 14 17.23 ±3.15 0.15 ±0.03 15 43.49 ± 16.20 0.28 ± 0.06 Graphical representations of MOE and MOR against density are shown in figures 3 and 4. The data presented in figures 3 and 4 confirms the expected increase in strength with density and shows that there is a lower limit on density for a coherent board using the process outlined. It is shown that the 5 % aerogel addition does not appear to affect strength, whereas the 10 % addition does affect strength of the board. For similar densities the strength is reduced with the 10 % aerogel addition. However, the addition of the MFC is shown to increase both density and strength of the boards. It was also notable that the surface of the boards with MFC was less friable. Further sub samples of the wood fibre composite boards were tested to determine thermal conductivity. Sub samples of each board were cut into 300 mm x 300 mm squares. The samples were placed in a Fox 300 thermal testing unit to determine thermal conductivity (A) over a 20°C temperature difference (5-25 °C). At least three replicate readings were taken, and the mean value determined for each board. The R value of each board was calculated using the thermal conductivity measurements using the following formula, where I = thickness (m) and A = thermal conductivity (W / mK). To improve accuracy during comparison, the R value per metre thickness was calculated for each batch. Data for thermal conductivity, R value and R per metre are given in Table 4 below. Table 4 Thermal conductivity and R values of boards Batch Mean Thermal conductivity (W / mK) (m2K / W) R per metre (m2K / W) 1 0.0418 ± 0.0014 0.59 23.90 2 0.0439 ± 0.0013 0.55 22.80 3 0.0457 ± 0.0008 0.52 21.87 4 0.0420 ± 0.0010 0.57 23.82 5 0.0440 ± 0.0010 0.54 22.73 6 0.0475 ± 0.0012 0.50 21.05 7 0.0428 ± 0.0009 0.54 23.37 8 0.0449 ± 0.0011 0.54 22.29 9 0.0535 ± 0.0005 0.44 18.70 10 0.0534 ±0.0024 0.45 18.73 11 0.0534 ±0.0000 0.45 18.72 12 0.0522 ± 0.0014 0.46 19.16 13 0.0468 ± 0.0005 0.49 21.37 14 0.0484 ± 0.0016 0.48 20.65 15 0.0538 ±0.0018 0.43 18.60 The R value of the boards compared to density is shown in the graph of Figure 5. Normally, it would be expected that less dense materials would have higher R value and form better insulators. Since board thickness affects R values, a control for thickness is taken into account by using an R value per metre thickness as shown in the graph of Figure 6. The data demonstrates that the R value of the boards decreases with density in a relatively linear fashion until a minimum R value of between around 18 and 19 m2K / W. It is shown that there is minimal effect on insulation of 5 wt% aerogel addition. However, at 10 wt% aerogel addition there does appear to be a difference in the trend, with the 10 wt% addition showing a higher R value when compared with similar density boards. Also, addition of the MFC is shown to reduce the R value. The most likely explanation for the decrease in R value is the increase in density affected by the addition of MFC. The apparent increase in relative R value of the 10 % addition was tested using simple statistical methods. The five composite boards that fall in the 150 to 200 kg / m3 density range were compared: B3 (control), B6 (5 wt% aerogel), B8, (10 wt% aerogel) B13 (5 wt% aerogel / MFC) and B15 (5 wt% aerogel / MFC). An Anova test showed there is some significant (p=0.002) difference between the R values per metre. A series of T-tests showed that the B8 board has a significantly higher R value per metre than the B6, B13 and B15 boards and is not significantly different to the B3 board. Table 5. Significance of differences between boards in the 150 - 200 kg / m3 range. (Key: orange - no significant difference; green - significant difference). B3 B6 B8 B13 B15 B3 (Control) Black Grey Grey Grey Grey B6 (5%) Orange Black Grey Grey Grey B8 (10%) Orange Green Black Grey Grey B13 (5+5%) Orange Orange Green Black Grey B15 (5+5%) Green Orange Green Orange Black It can be concluded that the 10 wt% aerogel (within the stated density range) had a R value significantly higher or the same as boards with a lower density, which goes against the trend in results. The five composite boards that are within the 100-150 kg / m3 range were compared: B1 (Control), B2 (control), B4 (5 wt%), B5 (5 wt%) and B7 (10 wt%) An Anova test showed no significant difference between boards (p=0.12). A T-test series showed that the B5 (5 wt%) board has a significantly lower R value than B1, B4 and B7 whilst the B7 (10 wt%) board showed no significant difference to any of the boards in this density range. Table 6. Significance of differences between boards in the 100- 150 kg / m3 range. (Key: orange - no significant difference; green - significant difference). B1 B2 B4 B5 B7 B1 (Control) Black Grey Grey Grey Grey B2 (Control) Orange Black Grey Grey Grey B4 (5%) Orange Orange Black Grey Grey B5 (5%) Green Orange Green Black Grey B7 (10%) Orange Orange Orange Orange Black Three boards have a lower density than the 10 wt% board so it can be inferred that the addition of 10 wt% aerogel is having a positive effect on thermal properties. The following conclusions can be derived from the research (above) when forming a wood fibre composite using the specified parameters, method of manufacture and source materials: - MFC addition at 5 wt% increases board strength but reduces insulation properties; - aerogel addition at a minimum level of 10 % increases the insulation properties, but also reduces mechanical strength; - a balance between MFC concentration and aerogel addition (greater than 10 wt%) is required to produce a board having the required balance between mechanical and thermal properties. Experiments have also identified important technical considerations: - blowline addition of the aerogel and MFC in solution is possible although pumps should be selected with sufficient power and throughput according to the quantities of base materials; - additive mixtures need to be well mixed and / or freshly made; and - there is a minimum density of board that can be produced with adequate handling properties using the specified method. The invention is not limited to the specific examples described herein. Modification and / or improvements may be made without departing from the scope of the invention. Some further examples of alternative materials and processes are outlined below. According to an alternative embodiment, recycled wood fibres are used. Wood fibres were sourced from MDF Recovery Ltd, UK. by recycling waste MDF (medium density fibreboard). The recycling process produces recycled wood fibres having length of 0.5 to about 3mm. This is similar to lengths of commercially available virgin wood fibres. According to an experiment using recycled MDF wood fibres, batches of recycled fibres were assessed visually to identify any fibre clumps (known as shives). Batches with excessive shives were processed to remove shives. Fibre characterisation was conducted by IR spectroscopy. A known mass of fibres was suspended in a known volume of water. This suspension was then passed through an infrared (IR) characterisation system in which two IR beams were oriented co-planar and perpendicular to the flow of liquid and fibres in a measuring cell. Fibre length was determined by assessing time for fibres to pass through the beam, and width was calculated by the amount of IR absorbance. Scanning electron microscopy (SEM) was used to assess directly fibre separation and general quality of the recycled fibres. MDF recovered fibres were found to have a shive content of 22 %, as compared to standard commercial virgin fibres which have a shive content of 24 %. The results confirmed that the recovered MDF fibres were a suitable environmentally sound substitute for commercially available virgin fibres. According to another embodiment, aerogel particles are obtained from commercial suppliers, namely Enersens for their Kwark® product. Various grades of particles are available, from mm scale particles to 100 micron powder, as shown in the table 7 below. Table 7 Product Type Product grade Product Specification Granule Kwark® GL < 3500 pm Kwark® GM 1250-3500 pm Kwark® GS < 1250 pm Powder Kwark® XP 500 < 500 pm Kwark® XP 200 < 200 pm Kwark® XP 100 < 100 pm As a rule of thumb at least 10 layers of granules are needed for a given thickness of material. For example, if a sample is 10mm thick then the smallest granules (Kwark® GS) should be used. Research by the present inventors has shown that at high levels of aerogel, greater than around 25 wt%, the surface of the insulating composite board was found to be friable and prone to disintegration. According to another embodiment, the microfibrillated cellulose is obtained from the commercial supplier Borregaard®, Sarpsborg, Norway under the product designation Exilva® F01-L. This is supplied as a dispersion in water having the following characteristics: • Solid content - 2 % • pH (2 % in H2O) - 4.4 • Conductivity (2 % in H2O) - 92 uS / cm • Viscosity (2 % in H2O) - 29000 mPas • Water holding capacity (0.3 % in H2O) 87 g / g According to another embodiment, the resin binder used in the formulation is resorcinol formaldehyde adhesive. Other known resins such as isocyanates can also be used. According to another embodiment based on empirical data, thermal insulation and structural integrity may be further enhanced, by using refined soft wood fibres having a length between around 3 mm and 5 mm. Experiments conducted by the inventors demonstrate that wood fibre, silica-based aerogel, MFC and resin can be successfully mixed together to form a cohesive solid block with the required mechanical strength and thermal properties such that it would be suitable for use as board insulation in the construction industry (and elsewhere). According to a further embodiment of the invention, the base material is processed using an air-laying process to produce sheets of semi-flexible insulation. Trial production of insulation samples was undertaken using a Cormatex® nonwoven pilot line, incorporating “Lap Formair H” airlay technology. The pilot line has an opening and blending section, airlay forming sections and a thermobonding section. Following is a description of one example of a process by which insulation sheets can be manufactured. At the start of the production process, the base material is weighed and mixed in the required quantity with naturally derived (or ‘bio’) bi-component fibres. Bicomponent fibres are added as a resin to bind the material as well as provide structural integrity. According to the present embodiment, bio bi-component fibres constitute around 15 wt% of the composite material composition with the remaining 85 wt% being the base material comprising refined wood fibres coated with MFC and aerogel. An example of an individual bi-component fibre with a generally round crosssection is shown schematically at 30 in figures 7a and 7b. The bi-component fibre is a naturally derived polymer that is bio-degradable, which advantageously reduces the environmental impact of the formed insulation. The fibre 30 has a density of 1.25 g / cm3. The bi-component fibre 30 comprises an inner core 31 of polylactic acid (PLA Ingeo ™) with a melting point of 160 °C. The bi-component fibre 30 comprises an outer polymer sheath 33 of polybutylene succinate (PBS) and has a melting point of 116 °C. The outer sheath 33 has a melting point that is less than the melting out of the inner core 31 to ensure that the outer sheath 33 melts before the inner core 31 to bind the bi-component fibre 30 within the base material during processing, while the inner core 31 remains stiff to retain the shape of the fibre 30 within the resulting composite. Following weighing the base material (comprising refined wood fibres coated with MFC and aerogel) is mixed with the required quantity of bi-component fibres in a dry-mix process. A thorough mixing process is required to ensure an even distribution of the bi-component fibres 30 amongst the fibres of the base material. One example of such a process includes two stages of blending. A first stage involves entraining the fibres (base material and bi-component) within an air flow to cause turbulent mixing with several acute changes in direction and vertical portions where the fibres travel up and down portions of tubing within the air flow. A second stage involves mixing with mechanical aids. The air-flow with entrained fibres is sucked under negative pressure through a vertically oriented tubing and a mechanical mixing device in the form of rotating discs with interlocking teeth. At the end of the described two-stage mixing process the mixed material contains a thorough blend of base material and bi-component fibres evenly distributed within the material. The mixed fibres are laid onto a conveyer, which controls and weighs the required amount of material laid onto the surface of the conveyor to ensure the final insulation sheets are formed with the required density. The material passes at a controlled rate through a thermosetting oven set at a temperature of between 80 - 200 °C (depending on the properties of the bi-component fibres 30) to ensure melting of the outer sheath 33. The insulation sheet transits through the oven at a linear speed of no more than 15 m / min (depending on weight of the material). Melting of the outer sheath 33 occurs in the oven which binds the mixture of fibres into a sheet. Once the material exits the oven on the conveyor, the material is cooled and the outer sheath 33 sets into a solid to form a cohesive stable semi-flexible sheet of insulation. The resulting composite material is a sheet of relatively stiff self-supporting insulation that is semi-flexible and can be cut and bent into the required shape and form for the anticipated end use. The insulating sheet material can be formed with a thickness of up to around 150 mm. The optimal density range appears to be between around 30 kg / m3 and 80 kg / m3. The core 31 of the bi-component fibres 30 within the material remains stiff to provide structural strength and increase loft in the insulation sheets. Table 8 shows some test results recorded from initial trials forming sheet insulation on the pilot line. Tests were conducted under EN 12667:2002 using a Heat Flow Meter (HFM), with the sample placed between two plates and a temperature gradient is established over the thickness of the material. Heat flux transducers measured the heat flow inside the sample with a 20 °C temperature difference between the plates. Table 8 Run Batch Details Thickness Density Thermal Conductivity 3 6 UF+AERO 100mm 45 kg / m3 0.042 W / m2 4 6 UF+AERO 100mm 30 kg / m3 0.044 W / m 2 5 7 UF+AERO 50mm 65 kg / m3 0.037 W / m2 These initial test results indicate the insulation sheets with a density of 65 kg / m3 and a thickness of 50 mm display the optimal thermal performance. Advantageously, the air-laying trials showed that the insulation sheets formed using the described process are consistent and firm. According to other embodiments, various method steps may be combined to enhance efficiency of the insulation manufacturing process. For example, the method of coating the refined wood fibres with MFC and aerogel may be achieved on the same production line as the thorough mixing of bi-component fibres and subsequent heating and formation into a sheet of semi-flexible insulation. According to alternative embodiments, different types of bi-component fibres may be mixed with the base material prior to the air-lay process. For example, the bi-component fibre may be formed from polylactic acid (PLA) and modified co-PLA or any other material having the required properties.

Claims

Claims 1. An insulating composite material for thermal insulation, the insulating composite material comprising refined wood fibres, silica-based aerogel particles, a resin binder and microfibrillated cellulose, wherein the refined wood fibres are coated with silica-based aerogel particles and microfibrillated cellulose.

2. A material as claimed in claim 1, wherein the silica-based aerogel particles are hydrophobic and the silica-based aerogel comprises micro- or nano- crystalline cellulose.

3. A material as claimed in claim 1 or claim 2, wherein the aerogel content is between 8 and 25 wit%.

4. A material as claimed in any of the preceding claims, wherein the silica- based aerogel comprises particles have a largest diameter of less than 1500 microns.

5. A material as claimed in any of the preceding claims, wherein the MFC content is at least 3 wt%.

6. A material as claimed in any of the preceding claims, wherein the refined wood fibres have a size of between around 3 mm and 5 mm.

7. A material as claimed in any of the preceding claims, wherein the refined woad fibre content is between around 55 and 60 wt%.

8. A material as claimed in any of the preceding claims, wherein the wood fibres are recycled wood fibres.

9. A material as claimed in any of the preceding claims, wherein the resin binder comprises a setting polymeric material.

10. A material as claimed in any preceding claim wherein the material is in the form of compasite building insulation having a thickness of at least 5 mm.

11. An insulation board comprising the insulating composite material as claimed in any of the preceding claims and formed into insulation board.

12. A material as claimed in any of the preceding claims, wherein the insulating composite material in the form of insulation board has a density of between around 115 and 225 kg / m3.

13. A material as claimed in any one of claims 1 to 10, wherein the insulating composite material further comprises bi-component fibres, wherein each bi- component fibre has an inner core and an outer sheath, wherein the outer sheath has a lower melting point than the inner core.

14. A material as claimed in claim 13, wherein the bi-component fibres form between around 10 and 25 wit% of the combined material content.

15. An insulation sheet comprising the insulating composite material as claimed in any claim 13 or claim 14, and formed into semi-flexible insulation sheet.

16. An insulation sheet claimed in any claim 15, wherein the insulating composite material in the form of semi-flexible insulation sheet has a density of between around 35 and 80 kg / m?3.

17. A method of forming a composite material as hereinbefore described comprising: applying resin binder to refined wood fibres with a liquid mixture of silica based hydrophilic aerogel particles and microfibrillated cellulose in a turbulent flow of fluid to form a base material; reducing the moisture content of the base material; and forming and setting the base material into a composite such that the refined woed fibres within the composite are coated with aerogel particles and microfibrillated cellulose.

18. A method as claimed in claim 17, comprising the step of applying the resin binder and liquid mixture to the refined wood fibres via a blowline.

19. A method as claimed in claim 17 or claim 18, comprising the step of refining the wood fibres to produce wood fibres having a length within a range between around 0.5 and 5 mm.

20. A method as claimed in any one of claims 17 to 19, wherein the step of forming and setting the base material into a composite comprises simultaneously pressing and heating the material into a preselected form.

21. A method as claimed in claim 20, wherein the method includes the step of altering physical properties of the composite material by altering at least one of the following: thickness of press; temperature; and / or speed of the pressing step.

22. A method as claimed in any one of claims 17 to 19, wherein the method further includes mixing bi-component fibres into the base material.

23. A method as claimed in claim 22, wherein the step of forming and setting the base material into a composite comprises laying the required quantity of mixed base material and bi-component fibres onto a surface and heating the material to a predetermined temperature to form a sheet of insulation.

24. A method as claimed in claim 23, wherein the bi-component fibre comprises an inner core and an outer sheath having a lower melting point than the inner core and wherein the step of setting the base material into a composite comprises heating the material to a predetermined temperature between the melting point of the inner core and outer sheath of the bi- component fibres such that the outer sheath of the bi-component fibres melts to bind the composite material into a sheet of insulation.

25. A method of forming an insulating composite material, the method comprising the steps of: mixing refined wood fibres, particles, microfibrillated cellulose and a bonding agent in a stream of air to form a web of base material; and bonding the base material to form an insulating composite material.

26. A method as claimed in claim 25, wherein the bonding step may comprise one or more of the following methods: latex bonding, thermal bonding, and / or high-pressure bonding.

27. An insulating composite material resulting from the method claimed in any one of claims 17 to 26. Claims 1. An insulating composite material for thermal insulation, the insulating composite material comprising refined wood fibres, silica-based aerogel particles, a resin binder and microfibrillated cellulose, wherein the refined wood fibres are coated with silica-based aerogel particles and microfibrillated cellulose.

2. A material as claimed in claim 1, wherein the silica-based aerogel particles are hydrophilic and the silica-based aerogel comprises micro- or nano- crystalline cellulose.

3. A material as claimed in claim 1 or claim 2, wherein the aerogel content is between 8 and 25 wt%.

4. A material as claimed in any of the preceding claims, wherein the silica- based aerogel comprises particles have a largest diameter of less than 1500 microns.

5. A material as claimed in any of the preceding claims, wherein the MFC content is at least 3 wt%.

6. A material as claimed in any of the preceding claims, wherein the refined wood fibres have a size of between 3 mm and 5 mm.

7. A material as claimed in any of the preceding claims, wherein the refined wood fibre content is between 55 and 60 wt%.

8. A material as claimed in any of the preceding claims, wherein the wood fibres are recycled wood fibres.

9. A material as claimed in any of the preceding claims, wherein the resin binder comprises a setting polymeric material.

10. A material as claimed in any preceding claim wherein the material is in the form of composite building insulation having a thickness of at least 5 mm.

11. An insulation board comprising the insulating composite material as claimed in any of the preceding claims and formed into insulation board.

12. A material as claimed in any of the preceding claims, wherein the insulating composite material in the form of insulation board has a density of between 115 and 225 kg / m?.

13. A material as claimed in any one of claims 1 to 10, wherein the insulating composite material further comprises bi-component fibres, wherein each bi- component fibre has an inner core and an outer sheath, wherein the outer sheath has a lower melting point than the inner core.

14. A material as claimed in claim 13, wherein the bi-component fibres form between 10 and 25 wit% of the combined material content.

15. An insulation sheet comprising the insulating composite material as claimed in any claim 13 or claim 14, and formed into semi-flexible insulation sheet.

16. An insulation sheet claimed in any claim 15, wherein the insulating composite material in the form of semi-flexible insulation sheet has a density of between 35 and 80 kg / m?.

17. A method of forming a composite material as hereinbefore described comprising: applying resin binder to refined wood fibres with a liquid mixture of silica based hydrophilic aerogel particles and microfibrillated cellulose in a turbulent flow of fluid to form a base material: reducing the moisture content of the base material; and forming and setting the base material into a composite such that the refined wood fibres within the composite are coated with aerogel particles and microfibrillated cellulose.

18. A method as claimed in claim 17, comprising the step of applying the resin binder and liquid mixture to the refined wood fibres via a blowline.

19. A method as claimed in claim 17 or claim 18, comprising the step of refining the wood fibres to produce wood fibres having a length within a range between 0.5 and 5 mm.

20. A method as claimed in any one of claims 17 to 19, wherein the step of forming and setting the base material into a composite comprises simultaneously pressing and heating the material into a preselected form.

21. A method as claimed in claim 20, wherein the method includes the step of altering physical properties of the composite material by altering at least one of the following: thickness of press; temperature; and / or speed of the pressing step.

22. A method as claimed in any one of claims 17 to 19, wherein the method further includes mixing bi-component fibres into the base material.

23. A method as claimed in claim 22, wherein the step of forming and setting the base material into a composite comprises laying the required quantity of mixed base material and bi-component fibres onto a surface and heating the material to a predetermined temperature to form a sheet of insulation.

24. A method as claimed in claim 23, wherein the bi-component fibre comprises an inner core and an outer sheath having a lower melting point than the inner core and wherein the step of setting the base material into a composite comprises heating the material to a predetermined temperature between the melting point of the inner core and outer sheath of the bi- component fibres such that the outer sheath of the bi-component fibres melts to bind the composite material into a sheet of insulation.

25. A method of forming an insulating composite material, the method comprising the steps of: mixing refined wood fibres, silica based hydrophilic aerogel particles, microfibrillated cellulose and a bonding agent in a stream of air to form a web of base material; and bonding the base material to form an insulating composite material.

26. A method as claimed in claim 25, wherein the bonding step may comprise one or more of the following methods: latex bonding, thermal bonding, and / or high-pressure bonding.

27. An insulating composite material resulting from the method claimed in any one of claims 17 to 26.

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