Process for preparing a powder of material of natural origin

Abstract

A process for preparing a powder of a material of natural origin, which includes a step of treating a substance containing at least 70% by weight of one or more leather wastes in particle form in a twin-screw extruder, wherein a temperature profile is applied that increases from an initial temperature of between 10 and 40 C. up to a maximum temperature of between 60 and 120 C., in the presence of water in an amount such that the weight ratio of water to substance is between 0.20 and 6.

Claims

1. A method for preparing a powder of a material of natural origin, comprising a step of treating an initial substance containing at least 70% by weight of leather prepared from non-human animal skin by tanning, in particulate form, in a twin-screw extruder wherein a temperature profile is applied that increases from an initial temperature of between 10 C. and 40 C. in an entry zone of the twin-screw extruder, up to a maximum temperature of between 60 C. and 120 C. in a last kneading zone of the twin-screw extruder, in the presence of water in an amount such that the weight ratio of water to said initial substance is between 0.20 and 6.

2. The method according to claim 1, wherein the step of treating the initial substance is carried out in the presence of water in an amount such that the weight ratio of water relative to the initial substance is greater than or equal to 0.2 and less than 1.6.

3. The method according to claim 1, wherein the step of treating the initial substance is carried out in the presence of water in an amount such that the weight ratio of water relative to the initial substance is between 1.6 and 6.

4. The method according to claim 1, wherein said twin-screw extruder is a co-rotating screw extruder.

5. The method according to claim 1, wherein said initial substance is in particulate form with a grain size between 5 mm and 10 cm.

6. The method according to claim 1, wherein an input flow rate of said initial substance in particulate form into the twin-screw extruder is between 1 and 15 kg/h.

7. The method according to claim 1, wherein said twin-screw extruder includes at least two kneading zones.

8. The method according to claim 7, wherein a rotational speed of the twin-screw extruder screws is between 100 and 400 rpm.

9. The method according to claim 1, wherein said initial substance is placed in the presence of water by introducing an aqueous solution into the twin-screw extruder.

10. The method according to claim 9, wherein the aqueous solution contains an agent for decomplexing chromium-collagen complexes.

11. The method as claimed in claim 9, wherein the aqueous solution is introduced into the twin-screw extruder before a first kneading zone of said twin-screw extruder.

12. The method according to claim 1, comprising a step of drying an extrudate obtained following said treatment step.

13. The method as claimed in claim 1, wherein the step of treating the initial substance is carried out in the presence of water in an amount such that the weight ratio of water relative to the initial substance is equal to 0.25.

14. The method as claimed in claim 1, wherein the step of treating the initial substance is carried out in the presence of water in an amount such that the weight ratio of water relative to the initial substance is equal to 0.6.

15. The method as claimed in claim 1, wherein the initial substance comprises no polymer or polymer precursor substance, and it is not mixed with any polymer or polymer precursor substance during said step of treating in said twin-screw extruder.

16. The method as claimed in claim 1, wherein said twin-screw extruder does not include any die at the exit.

17. A method for preparing a powder of a material of natural origin, comprising a step of treating an initial substance containing at least 70% by weight of leather prepared from non-human animal skin by tanning, in particulate form, in a twin-screw extruder wherein a temperature profile is applied that increases from an initial temperature of between 10 C. and 40 C. in an entry zone of the twin-screw extruder, up to a maximum temperature of between 60 C. and 120 C. in a last kneading zone of the twin-screw extruder, in the presence of water in an amount such that the weight ratio of water to said initial substance is between 0.20 and 6, wherein the step of treating an initial substance is carried out in the presence of water in the amount such that the weight ratio of water relative to the initial substance is comprised between 0.2 and 0.6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features and advantages of the present disclosure will emerge more clearly in the light of the examples of implementation hereinafter, provided merely by way of illustration and not restriction of the present disclosure, with reference to FIGS. 1 to 2, wherein:

(2) FIG. 1 shows images obtained with a binocular magnifier of the initial substance (in a/) and of the final material obtained by a method according to the present disclosure from this substance (in b/).

(3) FIG. 2 shows curves obtained by DSC for a chromium-tanned calf leather powder sample, and powders obtained from this material by a method according to the present disclosure, using water alone or water supplemented with different sodium hydroxide concentrations.

DETAILED DESCRIPTION

(4) Materials and Methods

(5) Twin-Screw Extruder

(6) For the experiments described hereinafter, Clextral BC-21 twin-screw extruders with a 70 cm sleeve or Clextral BC-45 twin-screw extruders, equipped with 7 Parmilleux R heating modules and a DKM pump with a power of 0.37 kW for the water supply in the extruder, are used.

(7) In each of the extruders, a series of modules are assembled according to an arrangement ensuring an alternation of conveying zones and kneading zones.

(8) The conveying modules used are, according to the experiments, of the following type: forward-flighted screw with double-threaded trapezoidal groove (at least one of these modules is placed in first position in the extruder, at the starting substance feed input); forward-flighted screw with double-threaded U-shaped groove which achieve both conveying the substance but also compressing it by reducing the thread pitch; and/or reverse-flighted screw with perforated double-threaded U-shaped groove which push the substance through channels, which supplies very substantial shear stress.

(9) The kneading modules are of the bilobe mixer type.

(10) The substance to be treated is introduced into the extruder via a hopper associated with a calibrated scale.

(11) In each of these modules, the screw pitches are between 20 and 70 mm.

(12) Differential Scanning Calorimetry (DSC) Analysis

(13) The thermal DSC studies were carried out on a Mettler Toledo Star DSC apparatus in a medium-pressure capsule, with temperature scanning from 20 C. to 220 C. with a gradient of 20 C./min in a nitrogen stream.

(14) Moisture Content Measurement

(15) The moisture content of the initial substances and the materials obtained is measured on samples of between 2 and 4 g in mass, in an aluminum cup, by means of a Mettler infrared moisture analyzer.

(16) Infrared-Attenuated Total Reflectance (IR-ATR) Spectrometry Analysis

(17) This analysis, making it possible to identify the amount of each protein conformation, to determine whether the transition of the helixes into random coils and sheets is effective, is carried out with a Thermo Fischer Nicolet 5700 infrared spectrometer, with ATR System, equipped with a diamond tip. The study interval is from 600 to 4000 cm.sup.1 and the resolution 4 cm.sup.1. A blank is carried out before each measurement, and at least 30 analyses are carried out for one spectrum, by observing the decomposition at amide peak 1 between 1570 and 1777 cm.sup.1, using data processing and analysis software.

(18) Bulk Density Measurement

(19) The bulk density of the powders is measured with the tapped density test, whereby a known mass of powder, between 20 and 100 g, is introduced into a graduated test tube mounted on a Densi-tap, and 2500 taps are applied in 10 min on the test tube. The final volume of the powder is read, as well as the weight thereof, and the bulk density thereof is inferred therefrom.

(20) Grain Size Measurement

(21) The grain size is measured by means of a vibrating screen. More specifically, a series of screens marketed by Retsch of the following respective sizes is used: 0 mm; 0.032 mm; 0.063 mm; 0.125 mm; 0.250 mm; 0.500 mm; 0.800 mm; 1.25 mm. Each screen is weighed empty and clean. Once the screens have been stacked in the order of increasing size, a sufficient amount of substance to cover the upper screen by approximately 1 cm is added. The vibration frequency is set to 70% of the maximum frequency and the vibration time is set to 10 min. Once the cycle has been completed, each screen is weighed with the retained powder grain size fraction, and the population mass distribution in each screen is determined.

(22) Flexural Test

(23) The flexural test is carried out on test specimens of the material to be tested, on a flexural test bench using the method described in the standard NF EN ISO 178-1:2011, with the following operating parameters: distance between the pressure points L=46 mm; force applied by the upper punch at a constant rate of 2.5 mm/min at 23 C.; 5 kN force sensor to record the force.
Hydric Characterization Test

(24) The hydric characterization test is carried out by submerging, in water at 25 C., square test specimens, having the dimensions 55 cm, of the material to be tested. The test specimens are weighed and measured before submerging, then every hour after initially submerging in water. After submerging for 24 hours, the test specimens are dried completely at 50 C., and the dry mass thereof is measured to define the potential substance loss by dissolving in water.

Example 1Leather Tanned with Plant-Based Tanning Agents

(25) The initial substance is leather of bovine origin, in the form of pieces of approximately 1 cm, of bulk density 0.21 g/cm.sup.3 and having a 13% moisture content.

(26) The Clextral BC-21 extruder is used for this experiment, with a rotational speed of the screws of 300 rpm. The screw profile is as follows (for each zone, the temperature profile is indicated between brackets): conveying (20 C.)-kneading (40 C.)-conveying (60 C.)-kneading (90 C.)-conveying (80 C.). The initial substance is introduced at the start of the first conveying zone, with a flow rate of 4 kg of dry substance/h. Water is introduced into the extruder at the kneading zone, with a flow rate of 3 l/h.

(27) At the extruder exit, a powder of material having a bulk density of 0.9 g/cm.sup.3 and a 10% moisture content is obtained with a flow rate of 4 kg/h.

(28) The IR-ATR analysis of the initial substance shows an helix structure at 38%, sheets at 20% and random coils at 42%. For the final material, the IR-ATR analysis shows an helix structure at 24%, sheets at 25% and random coils at 48%. This result confirms the change of protein structure in the substance during the implementation of the method according to the present disclosure.

(29) The powder obtained is shaped by thermocompression, at 150 C. and 80 MPa, of 12 g of powder in a steel mold. A part in the form of a solid block is thus obtained.

(30) The swelling rate in water of this part is determined according to the protocol described in the standard NF EN ISO 62.2, with the following few modifications: the test specimens used have dimensions of 55 cm and 3 mm of thickness; the water and the test specimens are kept at 25 C. and 60% humidity. Each test specimen is placed in a 11 capacity container, in 300 ml of distilled water. 72 hours before submerging, the containers containing the distilled water are placed under atmospheric conditions 25 C. and 60% humidity and the test specimens are dried at 50 C. After submerging, the dimensions of the test specimens and the masses thereof are recorded every hour over a 24-hour period. After 24 hours, the test specimens are oven-dried at 50 C. for 24 hours to measure the total substance loss and the final thickness once dried.

(31) A 16% swelling rate is thus determined. By way of comparison, the swelling rate obtained for a part formed by thermocompression of the initial substance, before implementing the extrusion method according to the present disclosure, according to the same protocol as that described above, is 42%.

Example 2Leather Tanned with Plant-Based Tanning Agents

(32) The initial substance is cow leather in the form of pieces of approximately 1 cm, of bulk density 0.2 g/cm.sup.3, of moisture content 16%.

(33) The Clextral BC-45 extruder is used for this experiment, with a rotational speed of the screws of 200 rpm. The screw profile is as follows: conveying at 20 C.-kneading (angular shift between the lobes 30) at 40 C.-conveying at 40 C.-kneading (angular shift 90) at 60 C.-conveying at 60 C.-kneading at 80 C.-conveying at 80 C. The initial substance is introduced at the start of the first conveying zone, with a flow rate of 6.5 kg of dry substance/h. Water is introduced into the extruder at the end of the first conveying zone, just before the first kneading zone, with a flow rate of 10/h.

(34) The extrudate obtained at the extruder exit is dried in a ventilated oven at 40 C. for 24 hours.

(35) A powder of material of bulk density 0.93 g/cm.sup.3, moisture content 8%, and of the following grain size distribution is obtained: 2% greater than 1.25 mm in size, 70% between 0.5 and 0.2 mm in size; 8% between 0.2 and 0.125 mm in size; 20% between 0.125 and 0.063 mm in size.

(36) The population of grains of powder having a grain size around 1 cm is shaped by uniaxial thermocompression at 150 C. and 80 MPa. The part obtained undergoes a flexural test. The following results are obtained: maximum stress 9.8+/0.6 MPa, bending modulus 1560+/150 MPa, deformation at rupture 1.35%+/0.07%.

(37) In comparison, for a part obtained by thermocompression, according to the same protocol, from the population of grains of less than 0.8 mm in size of the powder obtained at the end of the method of the present disclosure, the following mechanical characteristics are determined: maximum stress is 35+/1 MPa; bending modulus 2478+/370 MPa; maximum deformation 1.8%+/0.1%. These properties are substantially superior, in particular approximately 3.5 times superior as regards the maximum stress, to those obtained from the initial substance, not treated according to the present disclosure.

(38) As regards the water resistance, it is observed that the part formed by thermocompression from the material obtained at the end of the method according to the present disclosure has, compared to the part formed from the untreated initial substance, after submerging for 24 hours in water: a 22% mass gain instead of 44%; 10% swelling instead of 39%; a 6% irreversible mass loss instead of 10%; an irreversible swelling rate of 16% instead of 42%. The part formed by thermocompression from the material obtained by the method according to the present disclosure clearly has a substantially superior water resistance.

Example 3Chromium-Tanned Leather

(39) The initial substance is cow leather in the form of pieces of approximately 1 cm, of bulk density 0.20 g/cm.sup.3, and having a moisture content of 18%.

(40) The conditions used are identical to those of example 2, with the exception of the substance input flow rate into the extruder, which is 8 kg of dry substance/h.

(41) A powder of material of bulk density 0.4 g/cm.sup.3, moisture content 12%, and of the following grain size distribution is obtained: 16% of particles greater than 1.25 mm in size; 8.5% between 0.8 and 1.25 mm in size; 30.2% between 0.8 and 0.5 mm in size; 14.3% between 0.5 and 0.2 mm in size; 24% between 0.2 and 0.125 mm in size; 3% between 0.125 and 0.063 mm in size, 4% between 0.063 and 0.032 mm in size.

(42) The population of grains of powder having a grain size around 1 cm is shaped by uniaxial thermocompression at 190 C. and 80 MPa. The part obtained undergoes a flexural test. The following results are obtained: maximum stress 8.8+/3.1 MPa, bending modulus 1026+/373 MPa, deformation at rupture 2.4%+/0.6%.

(43) In comparison, for a part obtained by thermocompression, according to the same protocol, from the population of grains of less than 0.8 mm in size of the powder obtained by the method according to the present disclosure, the following mechanical characteristics are determined: maximum stress is 38.2+/0.4 MPa; bending modulus 2208+/59 MPa; maximum deformation 2.0%+/0.1%. These properties are much better, in particular approximately 4.7 times better as regards the maximum stress, than those obtained from the initial substance, not treated according to the present disclosure.

(44) As regards the water resistance, it is observed that the part formed by thermocompression from the material obtained by the method according to the present disclosure has, compared to the part formed from the untreated initial substance, after submerging for 24 hours in water: a 57% mass gain instead of 73%; 39% swelling instead of 95%; a 22% irreversible mass loss instead of a total loss of cohesion; an irreversible swelling rate of 36% instead of a total loss of cohesion. The part formed by thermocompression from the material obtained by the method of the present disclosure clearly has a substantially superior water resistance.

Example 4Pink-Colored Chromium-Tanned Leather

(45) The initial substance is calf leather in the form of pieces of approximately 1 cm, of bulk density 0.2 g/cm.sup.3, and having a moisture content of 13%.

(46) The conditions used are identical to those of example 2, with the exception of the substance input flow rate into the extruder, which is 7 kg of dry substance/h, the water feed rate, which is 9.8 l/h, and the temperature profile, which is as follows: conveying at 20 C.-kneading at 40 C.-conveying at 50 C.-kneading at 60 C.-conveying at 70 C. then 80 C.-kneading at 100 C.-conveying.

(47) Following the drying step, a powder of material of bulk density 0.32 g/cm.sup.3, substantially greater than that of the initial substance, and a 10% moisture content, is obtained.

(48) The powder is then shaped with conditions in a uniaxial thermopress at 180 C. and 81 MPa for 4 min.

(49) The part obtained has a bulk density of 1.34 g/cm.sup.3.

(50) In terms of mechanical performance of this part, the following values are measured, in comparison to those measured for a part obtained with the same protocol from the initial substance, not treated with the method according to the present disclosure: maximum flexural stress of 12.2 instead of 4.2 MPa, bending modulus of 1458 MPa instead of 443 MPa, maximum deformation of 3.4% instead 3%, shock resistance of 2.2 instead of 3. This decrease in the shock resistance clearly indicates that a more brittle and less fibrous material is obtained. Therefore, following the implementation of the method according to the present disclosure, there was indeed a modification of the internal structure of the proteins contained in the initial substance, ensuring superior cohesion of the material.

(51) FIG. 1 shows images obtained with a Nikon SNZ1500 binocular magnifier of the initial substance (in a/) and of the final material obtained (in b/). It is observed therein that the leather fibers have been transformed and agglomerated during the treatment step of the method according to the present disclosure.

Example 5Pink-Colored Chromium-Tanned Leather and Use of Sodium Hydroxide

(52) The initial substance is calf leather in the form of pieces of approximately 1 cm, of bulk density 0.2 g/cm.sup.3, and having a moisture content of 13%.

(53) The conditions used are identical to those of example 2, with the exception of the substance input flow rate into the extruder, which is 7 kg of dry substance/h, and the feed rate of aqueous solution introduced into the extruder.

(54) In this aqueous solution, the water is supplemented with sodium hydroxide NaOH. Several experiments are carried out, according to the parameters indicated in Table 1 below. The results obtained after the drying step, in terms of bulk density and moisture content of the powder after drying, are also indicated in Table 1.

(55) TABLE-US-00001 Experiment 1 2 3 4 Weight ratio of water 1.4 1.4 0.9 0.5 to initial substance Weight ratio of NaOH 0.025 0.05 0.032 0.019 to initial substance NaOH concentration 18 36 36 36 in water (g/l) Water feed rate (kg/h) 10.2 10.4 6.5 4 Bulk density of powder 0.41 0.42 0.43 0.40 obtained (g/cm.sup.3) Moisture content of powder 9 10 13 8 obtained (%)

(56) For all the experiments, it is observed that the bulk density of the material obtained is substantially greater than that of the initial substance. For all the experiments, it is furthermore greater than that of the powder obtained in example 4 above, without NaOH, from the same leather.

(57) For each experiment, the powder obtained is shaped as described in example 4, but at 170 C. and 81.5 MPa, and the parts formed are tested for the mechanical properties thereof. The results obtained are indicated in Table 2 below.

(58) TABLE-US-00002 Experiment 1 2 4 Maximum stress (MPa) 14.5 12.0 16.9 Bending modulus (MPa) 1630 1460 1432 Maximum deformation (%) 3.2 2.1 3.4

(59) Each of the powders of material obtained by the method, as well as the powder obtained in example 4, and the initial leather sample, are analyzed by DSC. The curves obtained are shown in FIG. 2. It is observed that, regardless of the conditions applied, the method of the present disclosure transforms the substance, as demonstrated by the disappearance of the endothermic peak.

Example 6Chromium-Tanned Leather with Pre-Moistening

(60) The initial substance is chromium-tanned calf leather in the form of pieces of approximately 1 cm, of bulk density 0.2 g/cm.sup.3, and having a moisture content of 16%.

(61) This substance is moistened in water in a concrete mixer for 12 h before the extrusion, in a cold chamber at 4 C. in a closed container. The amount of water is chosen to obtain a weight ratio of water to the substance equal to 1.

(62) The conditions used are identical to those of example 2, with the exception of the substance input flow rate into the extruder, which is indicated in Table 3 below, of the fact that no aqueous solution is introduced into the extruder, and of the temperature profile which is as follows: conveying at 20 C. then at 30 C.-kneading at 40 C.-conveying at 40 C. then at 50 C.-kneading at 60 C.-conveying at 60 C. then 70 C.-kneading at 80 C.-conveying.

(63) Two different experiments are carried out, according to the operating conditions indicated in Table 3. The characteristics of the powders obtained after drying are also indicated in this table.

(64) TABLE-US-00003 Experiment 1 2 Wet substance flow rate at input (kg/h) 10 12 Dry substance flow rate at input (kg/h) 5 6 Wet substance flow rate at exit (kg/h) 7.6 8.5 Moisture content of powder obtained (%) 12 12 Bulk density of powder obtained (g/cm.sup.3) 0.31 0.37

(65) For each of the experiments carried out, leather granules are obtained for which the DSC analysis confirms the denaturing of the collagen proteins which are contained therein (disappearance of the endothermic peak representative of the denaturing temperature of collagen on the DSC curves).

Example 7Chromium-Tanned Leather with Pre-Moistening

(66) The initial substance is chromium-tanned calf leather in the form of pieces of approximately 1 cm, of bulk density 0.2 g/cm.sup.3, and having a moisture content of 16%.

(67) This substance is moistened in water in a concrete mixer for 12 h before the extrusion, in a cold chamber at 4 C. in a closed container. The amount of water is chosen to obtain a weight ratio of water to the substance equal to 1.

(68) The Clextral BC-45 extruder is used for this experiment, with a rotational speed of the screws of 300 rpm. The screw profile is as follows: conveying at 20 C.-kneading at 30 C.-conveying with mixer at 40 C.-conveying at 80 C.-kneading at 80 C.-conveying at 80 C. then 90 C.-kneading at 90 C.-conveying at 80 C. with filtration-conveying at 80 C. The initial substance is introduced at the start of the first conveying zone, with a flow rate of 2.5 kg of dry substance/h. The extrudate obtained at the extruder exit is dried in a ventilated oven at 40 C. for 24 hours. The specific mass energy to which the material is subjected in the extruder is between 1136 and 1311 Wh/kg. The wet substance flow rate at the exit is 3 kg/h.

(69) A powder of material which has, after drying, a bulk density of 0.35 g/cm.sup.3, a moisture content of 11%, and the following grain size distribution is obtained: 0.3% of particles greater than 4 mm in size; 3.3% between 4 and 2 mm in size; 16.1% between 2 and 1.2 mm in size; 18.2% between 1.2 and 0.8 mm in size; 41.3% between 0.8 and 0.25 mm in size; 20.8% less than 0.25 mm in size. The population less than or equal to 800 m in size, which is predominant in this powder, can be isolated by screening.

Example 8Chromium-Tanned Leather Blend

(70) The initial substance is a blend of chromium-tanned calf leathers of different colors (red, blue, yellow, orange) in the form of pieces of approximately 1 cm, of bulk density 0.18 g/cm.sup.3, and having a moisture content of 13%.

(71) The extruder and the operating parameters are identical to those in example 7, apart from the following differences: the rotational speed of the screws is equal to 200 rpm and the initial substance is introduced at the start of the first conveying zone with a flow rate of 1.5 kg of dry substance/h.

(72) After the drying step, a powder of material having a bulk density of 0.35 g/cm.sup.3 and a 12% moisture content is obtained.

(73) The grain size distribution of the grains of powder is as follows: 1.4% greater than 4 mm in size; 5.5% between 2 and 4 mm in size; 14.6% between 1.2 and 2 mm in size; 22.2% between 0.8 and 1.2 mm in size; 34.5% between 0.25 and 0.8 mm in size; 21.8% less than 0.25 mm in size. The population less than or equal to 800 m in size, which is predominant in this powder, can be isolated by screening.

(74) The proportion of the population less than or equal to 800 m in size in the powder of material formed according to the present disclosure can be increased by applying, in one or more kneading zones, greater shearing forces on the substance.

(75) Applying the method according to the present disclosure once again to the powder of the material obtained by the method makes it possible advantageously to reduce further the grain size and the properties of this powder.

Example 9Series of Chromium-Tanned Leathers

(76) Different initial substances are treated successively in the extruder, with a rotational speed of the screws of 250 rpm and a screw/temperature profile which is as follows: conveying at 20 C.-kneading at 30 C.-conveying at 30 C.-mixing at 40 C.-conveying at 60 C.-kneading at 80 C.-conveying at 80 C.-kneading at 90 C.-conveying at 80 C.

(77) The initial substances all consist of pieces of approximately 1 cm in size of chromium-tanned calf leather of different colors, bulk density and moisture content: yellow leather (bulk density 0.17 g/cm.sup.3, moisture content 12%, 16.37 kg), then dark blue leather (bulk density 0.17 g/cm.sup.3, moisture content 12%, 17.56 kg), then orange leather (bulk density 0.18 g/cm.sup.3, moisture content 11%, 14.87 kg), then red leather (bulk density 0.18 g/cm.sup.3, moisture content 12%, 20.07 kg).

(78) The solid initial substance input flow rates are, for all the substances, 4.4 kg of dry substance/h. Water is introduced into the extruder at the end of the first conveying zone, just before the first kneading zone, with a flow rate of 3.3 l/h, except for the red leather, for which the water flow rate is 2.8 l/h. The weight ratios of water to initial substance are equal to 0.89 for the yellow, dark blue and orange leathers, and to 0.77 for the red leather.

(79) The extrudates obtained successively at the extruder exit have clearly distinct colors. These extrudates are dried in a ventilated oven at 40 C. for 24 hours.

(80) The characteristics of the powders of material obtained are indicated in Table 4 below.

(81) TABLE-US-00004 Initial Bulk Moisture substance density (g/cm.sup.3) content (%) Yellow 0.3 7 Dark blue 0.35 7 Orange 0.37 7 Red 0.31 7

Example 10Leather Cuttings Tanned with Plant-Based Tanning Agents

(82) The initial substance is a powder of leather cuttings of ovine origin in the form of fibers from 1 to 7 cm in length, of bulk density 0.17 g/cm.sup.3 and having a 13% moisture content.

(83) The conditions used are identical to those of example 7, with the exception of the dry substance input flow rate into the extruder, which is 4.35 kg/h, and the water input flow rate into the extruder, which is 2.5 kg/l. The rotational speed of the screws is 200 rpm.

(84) The final drying step is carried out at 50 C. for 24 hours.

(85) A material in dry paste form is obtained which is then ground in a knife mill on a 1 mm screen. The bulk density of the powder obtained after grinding in the knife mill is 0.81 g/cm.sup.3.

(86) The grain size distribution is as follows: 0.1% greater than 2 mm in size; 2.8% between 1.2 and 2 mm in size; 32.0% between 0.8 and 1.2 mm in size; 7.0% between 0.25 and 0.8 mm in size; 43.1% between 0.125 and 0.25 mm in size; 15.0% less than 0.125 mm in size.

Example 11Chromium-Tanned Leather Cuttings

(87) The initial substance is a powder of leather cuttings identical to that of Example 10.

(88) The conditions used are identical to those of example 7, with the exception of the dry substance input flow rate into the extruder, which is 4.2 kg/h, and the water flow rate, which is 3.6 l/h. The rotational speed of the screws is 250 rpm. The extruder is furthermore devoid of a filtration module.

(89) The final drying step is carried out at 50 C. for 24 hours.

(90) A material in the form of a powder having a density of 0.36 is obtained.

(91) The grain size distribution of this powder is as follows: 2.7% greater than 2 mm in size; 29.1% between 1.2 and 2 mm in size; 26.6% between 0.8 and 1.2 mm in size; 3.2% between 0.25 and 0.8 mm in size; 37.8% between 0.125 and 0.25 mm in size; 0.6% less than 0.125 mm in size.

Example 12Crocodile Leather Cuttings Tanned with Synthetic Agents

(92) The initial substance is a powder of crocodile leather cuttings tanned with synthetic agents, in the particulate form of fibers from 1 to 7 cm in length, of bulk density 0.06 g/cm.sup.3.

(93) The conditions used are identical to those of example 11, with the exception of the dry substance input flow rate into the extruder, which is 4.58 kg/h, and the water flow rate, which is 3.3 l/h. The rotational speed of the screws is 200 rpm.

(94) The final drying step is carried out at 50 C. for 24 hours. The material obtained then undergoes a grinding step in a knife mill.

(95) A material in the form of a powder having a density of 0.67 and a 5% moisture content is finally obtained. 41.6% of the grains of this powder have a grain size less than or equal to 0.8 mm.

Example 13Grey Chromium-Tanned Leather

(96) The initial substance is calf leather in the form of pieces of approximately 1 cm, of bulk density 0.2 g/cm.sup.3, and having a moisture content of 13.2%.

(97) The Clextral BC-45 extruder is used for this experiment, with a rotational speed of the screws of 300 rpm. The initial substance is introduced at the start of the first conveying zone, with a flow rate of 5.6 kg of dry substance/h. Water is introduced into the extruder at the end of the first conveying zone, just before the first kneading zone, with a flow rate of 2.32 kg/h. The weight ratio of water to initial substance is equal to 0.6. The temperature profile is as follows: conveying at 20 C., kneading at 30 C., conveying at 30 C., kneading at 40 C., conveying at 60 C., kneading at 80 C., conveying at 90 C., kneading at 90 C. and conveying at 80 C.

(98) The specific mass energy to which the substance is subjected in the extruder is between 1277 and 1345 Wh/kg. The wet substance flow rate at the exit is 6.76 kg/h.

(99) The extrudate obtained at the extruder exit is dried in a ventilated oven at 40 C. for 24 hours.

(100) Following the drying step, a powder of material of bulk density 0.6 g/cm.sup.3, substantially greater than that of the initial substance, and a 7.92% moisture content, is obtained.

(101) The grain size distribution of this powder is as follows: 4.2% greater than 2 mm in size; 46.7% between 1 and 2 mm in size; 20.2% between 0.8 and 1 mm in size; 10.8% between 0.5 and 0.8 mm in size; 1.2% between 0.25 and 0.5 mm in size; 15.6% between 0.125 and 0.25 mm in size; 1.4% between 0.032 and 0.125 mm in size.

Example 14Chromium-Tanned Calf Leather

(102) The initial substance is calf leather in the form of pieces of approximately 1 cm, of bulk density 0.20 g/cm.sup.3, having a moisture content of 13.5%.

(103) The Clextral BC-45 extruder is used, with a rotational speed of the screws of 300 rpm. The screw profile is as follows: conveying at 20 C.-kneading (angular shift between lobes 30) at 30 C.-conveying at 40 C.-kneading (angular shift 90) at 50 C.-conveying at 90 C.-kneading at 100 C.-conveying at 80 C. The initial substance is introduced at the start of the first conveying zone, with a flow rate of 7 kg of dry substance/h. Water is introduced into the extruder at the end of the first conveying zone, just before the first kneading zone, with a flow rate of 4.2 l/h (weight ratio of water to initial substance equal to 0.6).

(104) The extrudate obtained at the extruder exit is dried in a ventilated oven at 40 C. for 24 hours.

(105) A powder of material of bulk density 0.36 g/cm.sup.3, moisture content 8.4%, and having a homogenous grain shape is obtained. 52% of the grains are less than 1 mm in size.

(106) After shaping by uniaxial thermocompression at 150 C. and 80 MPa, as described in Example 2, a part is obtained which, when subjected to a flexural test, has a maximum stress of 18 MPa.

Example 15Calf Leather Tanned with Plant-Based Tannins

(107) The initial substance is calf leather in the form of pieces of approximately 1 cm, of bulk density 0.21 g/cm.sup.3, having a moisture content of 12.2%.

(108) The Clextral BC-45 extruder is used, with a rotational speed of the screws of 300 rpm. The screw profile is as follows: conveying at 20 C.-kneading (angular shift between lobes 30) at 30 C.-conveying at 40 C.-kneading (angular shift 90) at 50 C.-conveying at 90 C.-kneading at 100 C.-conveying at 80 C. The initial substance is introduced at the start of the first conveying zone, with a flow rate of 7 kg of dry substance/h. Water is introduced into the extruder at the end of the first conveying zone, just before the first kneading zone, with a flow rate of 4.2 l/h (weight ratio of water to initial substance equal to 0.6).

(109) The extrudate obtained at the extruder exit is dried in a ventilated oven at 40 C. for 24 hours, then milled in a mill.

(110) A powder of material of bulk density 0.7 g/cm.sup.3, moisture content 9.1%, and having a homogenous grain shape is obtained. 95% of the grains are less than 1 mm in size.

(111) After shaping by uniaxial thermocompression at 150 C. and 80 MPa, as described in Example 2, a part is obtained which, when subjected to a flexural test, has a maximum stress of 45 MPa.

Example 16Chromium-Tanned Calf LeatherWater to Substance Ratio=1.6

(112) The initial substance is chromium-tanned calf leather in the form of pieces of approximately 1 cm, of bulk density 0.18 g/cm.sup.3, having a moisture content of 12.63%.

(113) The Clextral BC-45 extruder is used, with a rotational speed of the screws of 300 rpm. The screw profile is as follows: conveying at 20 C.-kneading (angular shift between lobes 30) at 30 C.-conveying at 40 C.-kneading (angular shift 90) at 50 C.-conveying at 90 C.-kneading at 90 C.-conveying at 80 C. The initial substance is introduced at the start of the first conveying zone, with a flow rate of 7 kg of dry substance/h. Water is introduced into the extruder at the end of the first conveying zone, just before the first kneading zone, with a flow rate of 11.3 l/h (weight ratio of water to initial substance equal to 1.6).

(114) The extrudate obtained at the extruder exit is in the form of a blend of granules with a high moisture content (43%), having a grain size distribution such that: 80.7% of the granules are greater than 2 mm in size and 97.6% of the granules are greater than 1 mm in size.

Comparative Example 1Extrusion at Ambient Temperature

(115) The initial substance is a blend of chromium-tanned calf leathers of different colors (red, blue, yellow, orange) in the form of pieces of approximately 1 cm, of bulk density 0.18 g/cm.sup.3, and having a moisture content of 13%.

(116) The Clextral BC-45 extruder is used, with a rotational speed of the screws of 300 rpm. The temperature in the extruder is set to 25 C. The initial substance is introduced at the start of the first conveying zone, with a flow rate of 5 kg of dry substance/h. Water is introduced into the extruder at the end of the first conveying zone, just before the first kneading zone, with a flow rate of 3 l/h (weight ratio of water to initial substance equal to 0.6).

(117) A powder in the form of small fibers, of cottony appearance, with no shape homogeneity, is obtained, in which the grain size distribution is as follows: 25.2% of particles greater than 2 mm in size, 57.8% of particles greater than 1 mm in size, 42.2% of particles less than 1 mm in size.

(118) The DSC analysis of the powder obtained shows a lack of denaturing of the collagen proteins which are contained therein (no disappearance of the endothermic peak representative of the denaturing temperature of collagen on the DSC curve).

(119) After shaping by uniaxial thermocompression at 150 C. and 80 MPa, as described in Example 2, a part is obtained which, when subjected to a flexural test, has a maximum stress of merely 5 MPa, substantially lower than that obtained for the powders prepared according to the present disclosure.

Comparative Example 2Extrusion at Maximum Temperature Equal to 50 C.

(120) The initial substance is a blend of chromium-tanned calf leathers of different colors (red, blue, yellow, orange) in the form of pieces of approximately 1 cm, of bulk density 0.18 g/cm.sup.3, and having a moisture content of 13%.

(121) The Clextral BC-45 extruder is used, with a rotational speed of the screws of 300 rpm. The screw profile is as follows: conveying at 20 C.-kneading (angular shift between lobes 30) at 30 C.-conveying at 40 C.-kneading (angular shift 90) at 45 C.-conveying at 50 C.-kneading at 50 C.-conveying at 50 C. The temperature in the extruder is set to 25 C. The initial substance is introduced at the start of the first conveying zone, with a flow rate of 5 kg of dry substance/h. Water is introduced into the extruder at the end of the first conveying zone, just before the first kneading zone, with a flow rate of 3 l/h (weight ratio of water to initial substance equal to 0.6).

(122) A low-density, cottony powder, with long fibers, of which the shape factor differs substantially from one fiber to another, is obtained at the extruder exit.

(123) In respect of grain size, 18% of the particles are greater than 2 mm in size and 53.4% are less than 1 mm in size. The mechanical properties of this powder are not satisfactory. After drying, the bulk density of this powder is merely 0.23 g/cm.sup.3, substantially lower than that of the powders prepared according to the present disclosure.