Abstract
A microfibrillated cellulose-loaded foam is indicated, comprising microfibrillated cellulose, at least one thickening agent and/or at least one adhesive biopolymer. Furthermore, a method for producing such a microfibrillated cellulose-loaded foam and a use of such a foam are provided.
Claims
1. A microfibrillated cellulose-loaded foam comprising microfibrillated cellulose, at least one thickening agent and/or at least one adhesive biopolymer.
2. The microfibrillated cellulose-loaded foam according to claim 1, wherein the foam is a heat-dried foam.
3. The microfibrillated cellulose-loaded foam according to claim 1, wherein the dry foam has a density of between 0.05 and 0.35 g/cm.sup.3.
4. The microfibrillated cellulose-loaded foam according to claim 1, wherein the thickening agent is chosen from the group consisting of cellulose derivative, protein, polysaccharide, polyvinyl alcohol or polyethylene glycol or combinations thereof.
5. The microfibrillated cellulose-loaded foam according to claim 1, wherein the at least one biopolymer is a protein.
6. The microfibrillated cellulose-loaded foam according to claim 1, wherein the foam comprises further additives chosen from the group consisting of: an adhesive, an adhesive hardener, a sizing agent, a mold resistant compound, a fiber decay resistant compound, a heat resistant compound, an electricity resistant compound, an acid resistant compound, a smoke resistant compound or combinations thereof.
7. A method for producing a wet microfibrillated cellulose (MFC)-loaded foam, comprising the steps of: a) Providing a concentrate comprising microfibrillated cellulose, b) Feeding the concentrate into a foaming apparatus, c) Adding a liquid to the concentrate to obtain a suspension, d) Agitating and pressurizing the suspension in the foaming apparatus, e) Sparging a gas into the suspension, f) Discharging the suspension through an outlet in the foaming apparatus to obtain a microfibrillated cellulose-loaded foam, wherein the microfibrillated cellulose-loaded foam additionally comprises a thickening agent and/or adhesive biopolymer.
8. The method according to claim 7, wherein the adhesive biopolymer is added to the concentrate before step b).
9. The method according to claim 7, wherein the thickening agent is added to concentrate together with the liquid in step c).
10. The method according to claim 7, wherein the liquid is added in split streams.
11. The method according to claim 7, wherein the gas in step e) is added in its sub- or supercritical state.
12. The method according to claim 7 further comprising the step of casting the foam into a mold.
13. The method according to claim 12, wherein the cellulose foam is heat-dried.
14. The method according to claim 13, wherein the heat drying is microwave-assisted convection drying or microwave-assisted vacuum drying.
15. The method according to claim 7, wherein the MFC in the concentrate has a fiber content in the range of 7 to 20 wt. %.
16. The method according to claim 7, wherein further additives are added either in step a) and/or step c).
17. A method comprising using a foam according to claim 1 as an insulation material, packaging material or cushioning material.
18. A microfibrillated cellulose-loaded foam obtainable by a method according to claim 7.
19. The microfibrillated cellulose-loaded foam according to claim 2, wherein the foam is a microwave-assisted convection dried foam or a microwave-assisted vacuum dried foam.
Description
SHORT DESCRIPTION OF THE FIGURES
[0065] The invention will be described in more detail by the following exemplary embodiments in FIGS. 1 to 3B, without the invention being restricted to these embodiments. Same reference signs in the embodiment indicate same or similar objects. It shows:
[0066] FIG. 1: an exemplary process according to the invention;
[0067] FIG. 2A: compares the gas volume fraction and pore distribution at different formulations;
[0068] FIG. 2B: shows micro-CT images of the foams after fixation through freeze-drying according to FIG. 2A;
[0069] FIG. 3A: shows an image of a microwave-convection dried foam in a total perspective; and
[0070] FIG. 3B: shows a zoom of the foam of FIG. 3A.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0071] FIG. 1 shows an exemplary embodiment of the process according to the invention. The process 1 is performed by using a twin-screw extruder 11. The twin-screw extruder comprises a motor 11a, an inlet 11b in which the respective material can be fed, an extruder exit 11c in form of a nozzle, eleven barrels (barrels 3 to 7 are indicated) with a diameter of 30 mm and diameter-to-length ratio of 44, and a variety of further inlets 11d and 11d′ for adding further substances to the extruder. The temperature-controlled barrels are set to an operating temperature of 20° C. A powder composition comprising 92 wt. % of microfibrillated cellulose concentrate (containing 24 wt. % solids in water), 3 wt. % talc, 2 wt. % ethanol, and 3% egg white protein is added to a tank 12. Through an outlet 12a of the tank, the powder composition is continuously added to the extruder 11 at a mass flow rate of 3.5 to 4 kg/h via the respective inlet 11b and mixed by the screws of the twin-screw extruder 11. Through the inlets 11d at barrel 3 and 6, liquid is pumped into the extruder 11 from a liquid reservoir 13 at a mass flow rate of 8 to 8.5 kg/h. The liquid comprises water and 1% HPMC with a viscosity of approximately 400 mPas. The liquid is split into two streams 13a and 13b in approximately equivalents amounts. The addition of the liquids results in a viscous suspension of mainly fibrous material and a zero shear viscosity of approximately 10.sup.5 Pas. The suspension is conveyed towards the extruder exit 11c at a rotational speed of the extrusion screw of 40 U/min. A die at the extruder exit 11c with a diameter of below 1 mm and above 250 μm opposed a flow resistance, which results in an extrusion pressure of approximately 11 bar between barrel 5 and the extruder exit 11c. Further down in the process, carbon dioxide at a pre-pressure of minimum 20 bar is added from a gas reservoir 14 through pipe 14a into a further barrel 7 of the extruder via inlet 11d′. A control valve 14b allows adjustment of the flow rate of the carbon dioxide. The gas flow is approximately 40 g/h. The carbon dioxide is dispersed and dissolved in the suspension under pressure and acting shear flow between barrel 7 and extruder exit 11c. The carbon dioxide-suspension mixture is discharged from the extruder via the extruder exit 11c. The pressure drop to approximately 1 bar at the extruder exit 11c causes nucleation of gas bubbles and expansion of the foam, which can be casted into molds 15. The foamed product is released in an amount of 12 kg/h with a solid content of around 10 wt. %. The additives (talc, egg white protein, HPMC) in the solid fraction account for 25 wt. %. The gas volume in the foam is around 60 vol. %.
[0072] The casting in molds can be performed in a continuous process such as via conveyor belts. The molds with the foam can be placed into a microwave oven and dried using microwave-assisted convection drying.
[0073] It may be emphasized that the length of the extruder may vary, depending on the setup but has preferably a screw length L/screw diameter D ratio of L/D≥12, more preferably L/D≥20.
[0074] FIG. 2A compares the gas volume fraction and pore distribution at different formulations. Formulation 1 consists of 7.2 wt. % MFC, 1 wt. % egg white protein, 0.8 wt. % hydroxy propylmethyl cellulose, 1 wt. % talc particles, 0.6 wt. % ethanol and 89.4 wt. % water. Formulation 2 consists of 9.4 wt. % MFC, 0.6 wt. % hydroxy propylmethyl cellulose and 90 wt. % water. The gas volume fraction can be adapted by controlling the gas flow rate relative to the flow rate of liquid and solid stream in the extruder. The gas volume fraction increases with increasing relative gas flow rate. Formulation 2 (MFC+thickening agent HPMC) shows pronounced blow-by of gas (=gas loss) when increasing the gas volume fraction over 45%. In contrast, formulation 1 containing MFC, HPMC, egg white protein, talc and ethanol shows improved foaming behavior, reaching a gas volume fraction of up to 62%. The addition of egg white protein, talc and ethanol leads to better stabilization of the foam bubbles, resulting in higher gas holding capacity and smaller and more homogeneously distributed bubbles, as revealed by a micro-computer tomograph of freeze-dried extruded foam as shown in FIG. 2B (tomographs acquired with synchrotron X-ray tomographic microscopy at the TOMCAT, beam-line X02DA of the Swiss Light Source, Paul Scherrer Institute (Switzerland) with max. spatial resolution of 100 nm. Projections were acquired over 180° at an X-ray energy of 10.25 keV and an exposure time of 150 ms.).
[0075] FIG. 3 shows an extruded foam dried by microwave-convection drying with a bulk density of 0.108 g/cm.sup.3. The extruded foam consisting of 4 wt. % MFC, 0.8 wt. % HPMC, 1 wt. % talc particles, 2 wt. % egg white protein, 0.6 wt. % ethanol and 91.6 wt. % water was foamed in the extruder to reach a gas volume fraction of 62%. The foam was extruded into cylindrical molds (142 mL) and dried by microwave-assisted convection drying at 100° C. and 700 W microwave for 1 min followed by 100° C./500 W for 30 min or until fully dried. The application of microwave prevented that the volume decrease during drying is proportional to the decrease in water content. This resulted in a highly porous solid with a porosity of >90% consisting of 51 wt. % MFC, 26 wt. % egg white protein, 13 wt. % talc particles and 10 wt. % hydroxy propylmethyl cellulose. FIG. 3A shows the foam in a total perspective, FIG. 3B represents a zoom in perspective.
