WO2006009539A1

WO2006009539A1 - Lightweight acoustic and thermal insulation fluff and systems made thereof

Info

Publication number: WO2006009539A1
Application number: PCT/US2004/019657
Authority: WO
Inventors: Friedrich V. Pfister; Kurt Wyss; Thorsten Alts
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2004-06-16
Filing date: 2004-06-16
Publication date: 2006-01-26
Anticipated expiration: 2006-12-16

Abstract

The present invention relates to a thermal and/or acoustic insulation fiber fluff comprising: (i) at least from about 15 weight % to about 50 weight %, relative to the total weight of the fiber fluff, of a fibrillated fiber, and (ii) at least from about 50 weight % to about 85 weight %, relative to the total weight of the fiber fluff structure, of a coarse non fibrillating fiber, said fiber fluff structure having a loftiness ranging from about 50 cm3/m2 to about 500 cm3/m2 and a bulk density ranging from about 1.5 kg/m3 to about 30 kg/m3. The invention also relates to the process for making the above fluff and to thermal and/or acoustic systems based on the above fluff.

Description

TITLE

LIGHTWEIGHT ACOUSTIC AND THERMAL INSULATION FLUFF AND

SYSTEMS MADE THEREOF

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The invention relates to a lightweight fluff comprising a blend of fϊbrillated fibers and coarse non fibrillating fibers, to a process for preparing such fluff and to applications of such fluff in lightweight acoustic and thermal insulation systems. 2. Description of Related Art. hi many industries and applications, thermal and acoustic insulation structures are useful to dampen the noise and the heat produced by engine systems. Asbestos has been used for many years for such purposes. Nevertheless, for safety and health reasons, it would now be interesting to produce asbestos-free thermal and acoustic insulation structures.

Moreover, thermal and acoustic insulation structures of the art usually require layered structures of multiple materials to achieve good insulation across wide frequency and temperature ranges. As a consequence, they are very often expensive and heavy. Needle felt is a typical component for such a structure. Glass fiber, rock wool, ceramics are also used. They are of substantial weight and their stability is strongly compromised by engine vibrations.

Therefore, it would be interesting to produce at a low cost a thermal and acoustic insulation structure having a low density.

Li many transportation uses, reduction of weight is important to both reduce energy consumption and improve performance. High temperature resistant fibers, such as aramid, are known to perform particularly well. U.S. patent No. 4,957,794 discloses a fluff of aramid fibers wherein some of the aramid fibers are in the form of balls of the fluff.

Research Disclosure No. 22701 (March 1983) discloses a blend of para- aramid pulp and para-aramid staple in order to avoid the entanglement of para- aramid pulp during storage. But this kind of blend is still not optimized for acoustic insulation purposes. Therefore, it still remains problematic to obtain a good thermal and acoustic insulation system comprising a high temperature resistant fiber, presenting a very low density, and usable for instance in the automotive industry.

SUMMARY OF THE INVENTION

Now, it has been surprisingly found that a specific blend of (i) a fibrillated fiber and (ii) a coarse non fibrillating fiber, in particular a blend of (i) para-aramid pulp and (ii) meta-aramid crimped fibers, obtainable for example by dry mixing, could be used to obtain a specific, asbestos-free, lightweight fluff presenting very good thermal and/or acoustic insulation properties.

A first aspect of the invention is a thermal and/or acoustic insulation fiber fluff comprising: i) at least from about 15 weight % to about 50 weight %, relative to the total weight of the fiber fluff, of a fibrillated fiber, and ii) at least from about 50 weight % to about 85 weight %, relative to the total weight of the fiber fluff structure, of a coarse non fibrillating fiber, said fiber fluff structure having a loftiness ranging from about 50 cm³/m² to about 500 cnϊVm² and a bulk density ranging from about 1.5 kg/m³ to about 30 kg/m³. The loftiness and the bulk density (weight divided by volume) of the fluff structure of the invention are measured according to the methods described in Example 1.

Another aspect of the invention is a thermal and/or acoustic insulation system comprising: a) the fiber fluff structure as defined above; and b) a support structure.

A further aspect of the invention is a process for making the fluff structure of the present invention comprising the following steps: a) preparing, without mixing of any sort, a blend having a volume Vi and comprising i) from about 15 weight % to about 50 weight %, relative to the total weight of the blend, of a fibrillatable fiber and ii) from about 50 weight % to about 85 weight %, relative to the total weight of the blend, of a coarse non fibrillating fiber; b) measuring the volume Vi of the blend obtained under a); and c) expanding the blend obtained under a) by mixing it until a final volume of the blend Vf of at least twice Vi is achieved, to obtain the fluff structure of the present invention.

A still further aspect of the present invention is a process for making the thermal and/or acoustic insulation system according to the present invention comprising the following steps: a) preparing the fiber fluff structure as described above; b) combining the fluff structure obtained under a) with a support structure to obtain the thermal and/or acoustic insulation system of the present invention.

The fluff of the invention has high loftiness values and high resilient volumes at elevated fiber surface areas. The availability and excellent distribution in space of crimped fibers as well as the wide distribution of highly branched pulp fibers of different lengths and diameters enable the fluff of the invention to disperse and absorb, at highest efficiencies, acoustic and thermal waves passing in air at all frequencies. Furthermore, the fluff according to the present invention has very low thermal conductivity and is bondable both thermally and chemically, e.g., by means of tie resins.

The fluff according to the present invention is recyclable so that it can be used several times in e.g. aircraft maintenance cycles. This is excluded with conventional thermo-acoustic flame retardant insulation materials such as glass fibers.

Due to the particular lightness, it is expected that a significant weight saving is achievable when conventional thermo-acoustic flame-retardant materials based on glass fibers are replaced with the fluff according to the present invention in a typical large airplane. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a copy of a photograph of the fiber fluff structure according to the present invention taken at a magnitude of 258x (Fluff 1 of Example 1).

Fig. 2 is a description of the device of the heat insulation test of Example 2.

DETAILED DESCRIPTION

A first component of the fiber fluff structure of the invention is a fibrillated fiber.

By "fibrillated fiber" is meant, in the present invention, short fiber with a stem to which are attached fiber branches and fibrils. The stem has preferably a diameter ranging from 2 μm to 15 μm, more preferably a diameter of about 12 μm. Its length is preferably from 0.1 mm to 35 mm, and more preferably, from 0.2 mm to 8 mm. The fiber branches have preferably a diameter ranging from 1 μm to 10 μm. They are connected to the stem and can have fibrils attached to them. The fibrils have preferably a diameter ranging from 0.1 μm to 3 μm and a length greater or equal to 5 μm. Preferably, the surface area of the fibrillated fibers is greater than 1 m²/g, preferably greater than 5 m²/g, this surface area being measured according to the Brunauer, Emmett and Teller (BET) method as described in Example 1 below. The fibrillated fiber preferably includes cellulosic fibers, acrylic fibers, mineral fibers including ceramic fibers, para-aramid fibers and mixtures thereof. In a preferred embodiment of the invention, the fibrillated fiber is a para-aramid fiber. By "aramid" is meant a polyamide wherein at least 85% of the amide (-CO- NH-) linkages are attached directly to two aromatic rings. The preferred para- aramid is poly(p-phenylene terephtalamide) (PPD-T). By PPD-T is meant the homopolymer resulting from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the p-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyl chloride. In a preferred embodiment of the invention, the fibrillated fiber is a para- aramid pulp. Such para-aramid pulp may be prepared in accord with the teaching of U.S. patent Nos. 5,028,372 and 3,767,756, or by refining aramid floe. Examples of such para-aramid pulp are the products sold under the trade names Kevlar^® pulp merge 1F361 (average fiber length: 0.7-0.8 mm) or Kevlar^® pulp merge 1F538 (average fiber length: 1.17 mm, Canadian Standard Freeness of 260 ml) by E. I. du Pont de Nemours and Company, Delaware, U.S.A. The fibrillated fiber is preferably present in the fluff structure in a proportion ranging from about 20 weight % to about 40 weight %, preferably from about 20 weight % to about 30 weight %, relative to the weight of the fluff structure. In particular, the para-aramid pulp may be present in the fluff structure of the invention in an amount of about 20 weight % to about 30 weight %, preferably of about 23 weight % to about 27 weight %, relative to the weight of the fluff structure.

A second essential component of the fiber fluff structure of the invention is a coarse non fϊbrillating fiber.

By "coarse non fibrillating fiber", is meant in the present invention a fiber having a higher rigidity than the fibrillated fibers described above, thus allowing stability and firmness of the fluff. Preferably, the coarse non fibrillating fiber has a modulus of at least 200 cN/tex measured according to ASTM D 885-M/97 (EN 12562). Preferably, the coarse non fibrillating fiber has a diameter ranging from about 5 μm to about 100 μm and a surface area of less than, or equal to, 1 m²/g measured according to the BET method.

The coarse non fibrillating fiber preferably includes mineral fibers such as glass, wool fibers, cotton fibers, polytetrafluoroethylene fibers, polyester fibers, crimped meta-aramid fibers and mixtures thereof, hi a preferred embodiment of the invention, the coarse non fibrillating fiber is a meta-aramid crimped fiber. The preferred meta-aramid is poly(m-phenyleneisophtalamide) (MPD-I).

By MPD-I is meant the homopolymer resulting from mole-for-mole polymerization of m-phenylene diamine and isophthaloyl chloride and, also, copolymers resulting from blends of small amounts of other diamines with the m-phenylene diamine and/or from blends of small amounts of other diacid chlorides with the isophthaloyl chloride. By "crimped fibers" are meant, in the present invention, fibers that have been crimped and then cut at a predetermined length. Their length is preferably between 3 mm and 50 mm, and more preferably between 6 mm and 10 mm.

An example of such meta-aramid crimped fiber is the product sold under the trade name Nomex^® T450 by E. I. du Pont de Nemours and Company.

The coarse non fibrillating fiber is preferably present in the fluff structure in a proportion ranging from about 60 weight % to about 80 weight %, preferably from about 70 weight % to about 80 weight %, relative to the weight of the fluff structure. In particular, the meta-aramid crimped fiber of the invention is preferably present in an amount of about 70 weight % to about 80 weight %, preferably of about 73 weight % to about 77 weight %, relative to the weight of the fluff structure.

In a preferred embodiment of the invention, the fluff structure consists of: i) from about 20 to about 30 weight % of para-aramid pulp, relative to the total weight of the fluff structure, and ii) from about 70 to about 80 weight % of meta-aramid crimped fibers, relative to the total weight of the fluff structure.

The fluff structure of the invention may be prepared by mixing the coarse non-fibrillating fibers with the fibrillatable fibers. Preferably, the fluff structure of the invention is prepared by dry mixing the coarse non-fibrillating fibers with the fibrillatable fibers. However any other suitable mixing technique known by the skilled person can be used instead. The fibrillatable fibers may be already fibrillated, or all or part of them may become fibrillated during the process. In a preferred embodiment of the invention, the fibrillatable fibers are in form of a pulp of already fibrillated fibers and the coarse non fibrillating fibers are meta-aramid crimped fibers. The para-aramid pulp is preferably dry mixed with the meta-aramid crimped fibers so that the resulting fluff has a loftiness, as measured according to the method below, ranging from about 50 cm³/m² to about 500 cm³/m². hi the case when the drying mixing technique is applied, this can be implemented by means of a blender having mechanical blades and/or via high air turbulence. The mixing is continued until the final volume is at least twice the original volume, preferably four times the original volume, and more preferably ten times the original volume.

In a classical blender of the type Loedige, the mixing may take 20 min. In a high performance mixer such as a Model IH Ultra-Rotor mill sold by Jaeckering GmbH & Co. KG, of Germany, the same result may be obtained in 1 or 2 seconds. The mixing should be sufficient to get a good entanglement of the fibers but gentle enough not to damage the fibers or the pulp.

The fluff of the invention has a very homogeneous, uniform, structure. The fluff contains no agglomeration of substance. It has a bulk density of about 1.5 kg/m³ to about 30 kg/m³, preferably of about 3 kg/m³ to about 15 kg/m³. The fibrils from the fϊbrillated fibers and the fibrils from the open crimped fibers entangle each other very homogeneously, forming a resilient intimately blended structure.

The fluff structure of the invention has a loftiness (volume/surface area) ranging from 50 cm³/m² to about 500 cm³/m² measured according to the method described in Example 1.

The fluff structure of the invention has excellent acoustic properties at a very low density. It also has a very high acoustic absorption, heat and flame resistance, and thermal insulation properties. It has a good resilience. Test methods for such evaluations are set out below.

The fluff structure of the invention may comprise additional compounds. For instance, particularly in aeronautic applications where the fluff structure undergoes frequent mechanical vibration and may be applied without support elements in order to minimize the overall weight of the insulation system, bonding elements may be added in order to mechanically stabilize the fluff structure itself by bonding the crossover sites of the fibers, that is where the fibrillated fibers come in contact with the coarse non fibrillating fibers. Bonding elements can be of mechanical nature, such as meltable or partially meltable compounds, or of chemical nature, such as curable compounds. Meltable and partially meltable compounds include polyester powders, fibers including low melting sheath, polyphenylene sulfide fibers, and mixtures thereof. Curable compounds include phenolic resin, epoxy resin, and mixtures thereof. These compounds may be sprayed into the fluff or be added before producing the fluff. Upon exposure to appropriate heat, they then melt or cure within the fluff and, when cooled and solidified, they provide permanently enhanced structural integrity.

The thermal and/or acoustic insulation system of the invention comprises the fluff structure of the invention and a support structure. The support may be glue and the result may be used as a thermal and/or acoustic insulation plate.

The support structure may be any rigid or flexible structure associated to the fluff structure of the invention. The support may serve as a consolidation of the fluff structure. In the case the support defines a three-dimensional space, it may be filled with the fluff. The support preferably includes metal sheets or foils, films, fabrics, nonwovens, ceramics, paper, board, wood, plastic, membranes and combinations thereof. Fabrics include woven and/or knitted fabrics. Metal sheets include aluminum sheet, stainless steel, copper, magnesium, titanium and mixtures thereof. The support structure may be plain or perforated. The support may be made of one or more layers; it can also be a cover or a box.

In one embodiment of the invention, the system is a multilayered structure comprising at least one layer of fiber fluff structure, the support structure being made of one or more layers, films or sheets. The layers may be glued to one another or mechanically held together with a frame. Such systems may be manufactured by classical lamination of the layers constituting the system.

Preferably, the support structure of the system according to the present invention comprises three layers two of which form the external layers of the structure and one is an intermediate layer within the structure. Preferably the external layers are made of metal, and the fiber fluff structure is sandwiched between one of the external layers and the intermediate layer. Preferably, one of the two external layers is made of a porous metal sheet, more preferably of a perforated aluminum sheet. The intermediate layer is preferably made of a material capable of vibrating in the wave of acoustic. Such material includes metal foils and polyurethane foils. More preferably, the intermediate aluminum layer is made of an aluminum foil. The second of the two external layers is preferably adjacent to the intermediate layer and is made of an aluminum sheet. According to a preferred embodiment of the invention, the system is made of four layers in the following sequence:

A) a layer Ll of an aluminum sheet perforated with holes, wherein the holes represent 10 to 30%, by surface, relative to the surface of Ll, Ll having a thickness ranging from about 0.1 mm to about 0.5 mm;

B) a layer L2 of an aluminum foil having a thickness ranging from about 10 μm to about 30 μm;

C) a layer L3 of the fiber fluff structure of the invention having a thickness ranging from about 5 mm to about 40 mm; and D) a layer L4 of an aluminum sheet having a thickness ranging from about 0.1 mm to about 1 mm.

Alternatively, the system is a three-dimensional structure such as a pillow or a cover, filled with the fluff structure of the invention, the support being a fabric.

The system of the invention has excellent thermal and/or acoustic insulation properties. The thermal and/or acoustic insulation system of the invention is useful in a wide range of products including, as a few examples, high temperature insulation, absorbency applications, and so on. It can be used in houses, in pumps for swimming pools and in the automotive industry. It can be used to produce acoustic and/or thermal insulation panels for car engines and airplanes. In the process for making the thermal and/or acoustic insulation system of the invention, the combination of the fluff structure with the support structure (step (b)) may be achieved by any classical means. In a preferred embodiment of the invention, step (b) comprises: i) depositing a layer of the fluff structure on a porous band via air transportation, ii) pumping from said layer an appropriate amount of fluff structure with a vacuum robot, iii) depositing the amount of fluff structure on the support structure via the vacuum robot, iv) fixing the amount of fluff structure with the support structure.

The fixing of the fiber fluff structure to the support structure may be achieved by gluing, stitching or laminating the layers together. The fiber fluff structure may be stored in a container and then pumped and transported through pipes by air to the porous transport band. The design of fluff preferably conforms to the shape of the insulation panel to be manufactured. With this process, cutting of the fiber fluff is not necessary and the unused fiber fluff is transported back to the container for re-use. Therefore, no waste of fiber fluff structure is produced during the manufacture of the insulation part. Moreover, the fluff may be retrieved from used insulation panels after years and may subsequently be re-used.

The invention will be further described and compared with prior art in the following Examples and Comparative Examples.

EXAMPLES Description of the ingredients:

Pulp 1 : para-aramid pulp commercially available from E. I du Pont de Nemours and Company under the tradename Kevlar^® pulp merge 1F538 (average fiber length: 1.17 mm; Canadian Standard Freeness [TAPPI Test Method 227-M58] of 260 ml water overflow.

Floe 1 : para-aramid non crimped fibers having an average fiber length of 6.35 mm, a diameter of 15 μm and commercially available from E. I du Pont de Nemours and Company under the tradename Kevlar^® floe IF 107. Crimp 1 : meta-aramid crimped fibers having an average fiber length of

10 mm and a diameter of 15 μm and commercially available from E. I du Pont de Nemours and Company under the tradename Nomex^® T450.

EXAMPLE 1 Blends according to Table I were prepared. The figures are given in percentages by weight, relative to the weight of the blend.

TABLE I

For each blend, the components were mixed during 20 minutes in a Loedige mixer to obtain a fluff.

The bulk density, i.e., weight (kg) per volume (m³) was measured for each fluff fresh out of the mixer (uncompressed). The bulk densities of the four fluffs are collected in Table II (in which "comp." means "comparative") while the specific volumes of Fluff 1 and Fluff 4 are reported in Table HI:

TABLE π

Table II shows that the incorporation of 23% of para-aramid pulp in meta- aramid crimped fibers (Fluff 1) does not substantially affect the capability of meta- aramid crimped fibers to develop a very high volume under mixing. Therefore, with the invention, it is possible to obtain very voluminous structures having at the same time the properties attained due to the presence of the para-aramid pulp.

TABLE m

Table in shows that the replacement of para-aramid non crimped fibers (floe) by crimped meta-aramid fibers increases the capability of the blend to develop a high volume fluff by over 24% (from 196 to 244 dm³/kg).

Recovery and resilience: The resilience of Fluffs 1 and 4 was measured according to the following method: a cylinder having a volume of 1000 ml was filled up entirely with each fluff. The fluff was very slightly loaded with a cover plate of 7 g/cm² (having a diameter of 6.2 cm) during 16 hours (preconditioning). Then, the cover plate was removed and the fluff was compressed for 24 hours with a weight of 172 g/cm². The volume (Vl) was measured. Then the weight was removed and replaced by the 7 g/cm² cover plate. The new volume (V2) was measured after one minute and the volume regain (V2-V1) calculated. Volume regain divided by the fiber mass in the cylinder is defined as Recovery. After another 90 minutes of waiting the volume (V3) was measured (under the same load of 7 g/cm²). The volume regain (V3-V1) divided by the fiber mass in the cylinder is defined as Resilience. The results (change in volume per gram of fluff) are collected in Table IV:

TABLE IV

Table IV shows that the recovery and the resilience of the fluff are increased by replacing non crimped para-aramid fibers (floe) by crimped meta-aramid fibers.

The loftiness:

The loftiness of Fluffs 1 to 4 was determined according to the following method: 1) the surface area a [in m²/g] of Fluffs 1 to 4 was determined from nitrogen adsorption by the BET method using a model Strδhlein Surface Area Metre II from Strδhlein Kaarst-Dϋsseldorf (IF59). The fluffs were conditioned for the test by exposing them to a vacuum of less than 0.1 Torr for about 16 hours at about 80 °C. 2) the loftiness was calculated as specific volume/surface area according to the following formula: Loftiness = Volume/Surface

= 1 / (a * Bulk Density). The results are collected in Table V:

TABLE V

These results show that the loftiness of the fluff of the invention (Fluff 1) is increased by nearly 35% compared to that of comparative Fluff 4.

EXAMPLE 2

A system comprising the following four layers (in sequence) was manufactured: 1) Layer 1 : perforated aluminum sheet having a specific weight of about 0.6 kg/m², with a thickness of about 0.3 mm, wherein the holes represent about 26% of the surface of the sheet, 2) Layer 2: aluminum foil having a specific weight of about 0.054 kg/m², with a thickness of about 20 μm, 3) Layer 3: fiber fluff structure made of Fluff 1 of Example 1 and having a thickness as given in Table VI, and 5) Layer 4: aluminum sheet having a specific weight of about 1.35 kg/m², with a thickness of about 0.5 mm.

Three systems (Systems 1, 2 and 3) according to the invention were prepared by varying the fluff layer thickness (X). A comparative system (System 4) where Layer 3 was replaced by a classical acoustic absorbing inlay of glass having a density of 600 kg/m³ was also prepared.

The respective specific weights of the systems, depending on the thickness of the fluff layer (X value) are given in Table VI: TABLE VI

Table VI shows that the system according to the invention has a much lower specific area weight than usual thermal and acoustic insulation systems of the prior art.

Heat insulation test.

Systems 1 and 3 above were positioned at 25 mm distance from a cylindrical heat source surrounded by a heat insulated chamber as shown in Fig. 2. The temperature of the heat source was increased from 199.8⁰C to 700.0⁰C. The following temperatures were measured at stationary heat flow conditions: Tl: temperature of the heat source T2: temperature of Layer 2 (on side to Fluff 1) T3: Temperature of Layer 4 The results are given in Tables VII and VIE. The % of shielding is calculated according to the following formula: % shielding = -100 * (T3-T2)/T2. System 1: (10 mm FMfI)

TABLE Vn

System 3: (20 mm Fluff 1)

TABLE Vm

Tables VII and VTfI show that the systems of the invention have very good thermal insulation properties. Moreover, the higher the temperature of T2, the more significant the shielding.

Acoustic absorption test:

This test was conducted in an Alpha Cabin developed by and available from company Rieter (Switzerland). Samples of 1.2 m² of material are put into a rigid frame in the center of a reverberation room (the Alpha Cabin), constructed according to the big and normed reverberation room of the EMPA (Eidgenossische Material Priifungsanstalt in Dϋbendorf, Switzerland). The Alpha Cabin is air conditioned at 23°C and maintained at a relative humidity of about 50%. Three loud speakers diffuse acoustic energy within the Alpha Cabin. Part of the incident acoustic energy is absorbed by the material and redistributed within the Alpha cabin. The reverberation time is measured and compared to the reverberation time measured when the Alpha Cabin is empty. The absorption coefficient a is calculated according to the following formula: a = l-(Er/Ei), wherein Ei is the incident acoustic intensity and Er is the reflected acoustic intensity. This coefficient is measured for a pulse like noise frequency varying from 400 Hz to 10 kHz. The closer to 1 the coefficient is, the better the acoustic absorption is.

The following systems 5-10 were tested. Systems 5-7 are systems according to the invention. Systems 8-10 are comparative systems.

System 5: comprises only one layer Ll.

- Ll : 10 mm layer of fiber fluff structure made of Fluff 1 of Example 1. System 6: comprises the following two layers: - Ll: same as Ll of system 5.

- L2: aluminum foil having a specific weight of about 0.054 kg/m , with a thickness of about 20 μm.

System 7: comprises three layers in the following sequence:

- Ll : same as Ll of system 5. - L2: same as L2 of system 6.

- L3: perforated aluminum sheet having a specific weight of about 0.6 kg/m², with a thickness of about 0.3 mm, wherein the holes represent about 26% of the surface of the sheet.

System 8: comprises only one layer LIa. - Ll a: 4.8 mm layer of glass fiber fleece having a specific weight of

0.6 kg/m². System 9: comprises the two following layers:

- LIa: same as Ll a of system 8.

- L2a: aluminum foil having a specific weight of about 0.054 kg/m², with a thickness of about 20 μm.

System 10: comprises three layers in the following sequence:

- LIa: same as LIa of system 8. - L2a: same as L2a of system 9.

- L3a: perforated aluminum sheet having a specific weight of about 0.6 kg/m², with a thickness of about 0.3 mm, wherein the holes represent about 26% of the surface of the sheet.

The results are collected in Tables IX and X:

TABLE DC

TABLE X

The values for the absorption coefficient for the fiber fluff structure of the invention in Table DC are higher for low frequencies than those for the glass fiber fleece of the prior art in Table X. For automotive applications, heat shields with improved acoustic absorption at low frequencies and with low weight are highly desirable.

Claims

CLAIMSWhat is claimed is:

1. A thermal and/or acoustic insulation fiber fluff comprising: i) at least from about 15 weight % to about 50 weight %, relative to the total weight of the fiber fluff, of a fibrillated fiber, and ii) at least from about 50 weight % to about 85 weight %, relative to the total weight of the fiber fluff structure, of a coarse non fibrillating fiber, said fiber fluff structure having a loftiness ranging from about 50 cm³/m² to about 500 cm³/m² and a bulk density ranging from about 1.5 kg/m³ to about 30 kg/m³.

2. The fluff of claim 1 , wherein the fibrillated fiber is a para-aramid pulp.

3. The fluff of claim 1 or 2, wherein the coarse non fibrillating fiber is a meta- aramid crimped fiber.

4. The fluff of any preceding claim, consisting of: i) from about 20 to about 30% by weight of para-aramid pulp, relative to the total weight of the fluff structure; and ii) from about 70 to about 80% by weight of meta-aramid crimped fibers, relative to the total weight of the fluff structure.

5. The fluff of any preceding claim, wherein the bulk density ranges from about 3 kg/m³ to about 15 kg/m³.

6. A thermal and/or acoustic insulation system comprising: a) a fiber fluff according to any claim 1 to 5; and b) a support structure.

7. The system of claim 6, wherein the support structure includes one or more materials selected from metal sheets, metal foils, films, fabrics, nonwovens, ceramics, paper, board, wood, plastic, membranes and combinations thereof.

8. The system of claim 6 or 7, wherein the support structure comprises three layers two of which form the external layers of the system and one of which is an intermediate layer within the system, the fiber fluff being sandwiched between one of the external layers and the intermediate layer.

9. Thermal and/or acoustic insulation system comprising, in the following sequence:

A) a layer Ll of an aluminum sheet perforated with holes, wherein the holes represent 10 to 30%, by surface, relative to the surface of Ll, Ll having a thickness ranging from about 0.1 mm to about 0.5 mm; B) a layer L2 of an aluminum foil having a thickness ranging from about 10 μm to about 30 μm;

C) a layer L3 of a fiber fluff according to any claim 1 to 5, L3 having a thickness ranging from about 5 mm to about 40 mm; and

D) a layer L4 of an aluminum sheet having a thickness ranging from about 0.1 mm to about 1 mm.

10. A process for making a fiber fluff of any claim 1 to 6, comprising' the following steps: a) preparing, without mixing of any sort, a blend having a volume Vi and comprising i) from about 15 weight % to about 50 weight %, relative to the total weight of the blend, of a fibrillatable fiber and ii) from about 50 weight % to about 85 weight %, relative to the total weight of the blend, of a coarse non fibrillating fiber; b) measuring the volume Vi of the blend obtained under a); and c) expanding the blend obtained under a) by mixing it until a final volume of the blend Vf of at least twice Vi is achieved, to obtain the fluff structure of any claim 1 to 6.

11. The process of claim 10, wherein the blend obtained under a) is expanded under step c) so that Vf is at least four times Vi.

12. The process of claim 10 or 11 , wherein the blend obtained under a) is expanded under step c) by dry mixing.

13. A process for making a thermal and/or acoustic insulation system of any claim 6 to 8 comprising the following steps: a) preparing a fluff structure according to the process of any claim 10 to

12; b) combining the fluff structure obtained under a) to a support structure to obtain the thermal and/or acoustic insulation system according to any claim 6 to 12.

14. Process of claim 13, wherein step b) comprises: i) depositing a layer of the fluff structure obtained under a) on a porous band via air transportation; ii) pumping from the layer obtained under i) an appropriate design of fluff structure with a vacuum robot; iii) depositing the design of fluff structure on the support structure via the vacuum robot; iv) fixing the design of fluff structure to the support structure.