• Thermoplastic polymer (e.g. polypropylene PP) The main problems refer to a high viscosity, which leads to a difficult wetting while high temperatures can damage or destroy the fibers. Nevertheless a low price, reasonable processing temperatures and recyclability are reasons for a growing interest in thermoplastics and they are likely to replace the thermosets.

 

The manufacturing process mostly takes place in two steps, one for structuring the fiber arrangement and one for consolidating the structure. In the first step "hybrid fleeces" are produced by nonwovens technologies (e.g. carding/air laid and needlepunching). In a second step the hybrid fleece is heated mostly between two heated plates using certain compression. Sometimes a preheating either using hot air or radiation is combined. The heat is necessary to melt the thermoplastic material or to start the reaction of this thermosetting material, when a phenolic resin is used.

The main manufacturing processes presently used for the production of plant fiber composites are:

• Compression molding, applicable to resinated fiber mats, hybrid mats (PP/natural fibers), NMT (Natural fiber Mat reinforced Thermoplastic) comparable to GMT (Glass fiber Mat reinforced Thermoplastics)
• Structural Reaction Injection Molding (S-RIM)
• Injection Molding with short fiber reinforcement [5]

 

Compression molding is most used, in different variants: (I) using a pre-melted polymer, (2) using a fibrous polymer that is combined with the plant fibers into a hybrid mats before compression molding and (3) others use polymer powders that are introduced into the fiber mats before compression molding. Some typical productions lines are: Hermann Process (Laroche), Fibroline, etc.

 

3.3 Bulky wadding acoustical parts:

 

Air laid is the most appropriate technology to process such high loft products due to the following advantages: equilibrate MD/CD ration, suitability to process any type of automotive fibers (especially recycled fibers) and a thick, voluminous product can be produced with a high productivity. Machine manufacturers such Fehrer, Laroche, Fibroline, etc offer complete airlaid lines. Example of application: on the door panel.

 

4. Summary:

 

There is already a high penetration of nonwovens in automotive sector and the present paper only refers to the specific case of sound insulation. For each application there is still room for value added products and that will only further consolidate nonwovens' position.

 

When they have to choose between varieties of products, manufacturers consider following criteria: economics, durability, aesthetics, possibility, moldability, added benefits (e.g.: acoustics, flame retardant, recyclable, etc.), which are main driving forces of nonwovens in automotive industry worldwide. However, some studies [6] highlighted certain differences regarding the driving forces of different market (e.g. European and NAFTA), thus the penetration of nonwovens for some applications will be different: e.g. nonwovens are highly penetrated European headliner floor surface applications and weight save (gas reduction) pressure is higher in Europe while acoustic performances and cost save pressure are equally higher in Europe&NAFTA.

 

Recycling is at the moment a significant Europe driver not yet U.S. driver. EU regulations on the disposal of used cars are effective from I st July 2002. They focus on the re-use of textiles from used cars and on recycling materials in new cars. It requires that by the year of 2006 at least 85% of an automobile's weight to be recycled.

As the textile materials currently used in motor vehicles represent low quantities, one cannot expect them to become economically recycled because themselves consist of 2 to 5 fiber components blends and they are moreover combined with non-textile materials (metal, plastic materials) thus not very cost-effective to dissemble. Besides that, due to ageing and contamination, these textiles have, in many cases, no value with regard to recycling. In this respect, EU regulation offers the framework to solve these problems and open up a chance for the textile industry.