WO2001083194A1

WO2001083194A1 - Method for the extrusion of a fibre-filled polymer composition

Info

Publication number: WO2001083194A1
Application number: PCT/NL2001/000336
Authority: WO
Inventors: Hermanus Antonius Wallink; Petrus Henricus Maria Elemans; Markus Johannes Henricus Bulters; Gerrit Rekers; Jozef Johannes Franciscus Maria Kersemakers
Original assignee: Dsm N.V.
Priority date: 2000-05-03
Filing date: 2001-05-02
Publication date: 2001-11-08
Also published as: AU2001255104A1

Abstract

The invention relates to a method for extruding a polymer composition filled with brittle fibres, with the aid of an extruder to obtain a moulded article. The invention is characterised in that the brittle fibres have a length of 0.8-100 mm and in that the polymer composition is first of all preheated to a temperature of at least 80 °C, and preferably to close to the melting or softening temperature of the polymer, before the polymer composition is fed to the extruder and is extruded.

Description

METHOD FOR THE EXTRUSION OF A FIBRE-FILLED POLYMER

COMPOSITION

The invention relates to a method for extruding a polymer composition filled with brittle fibres, with the aid of an extruder to obtain a moulded article. The invention also relates to a moulded article thus obtained.

Extruding of a polymer composition filled with brittle fibres is already known in itself.

It has been found that when use is made of long, brittle fibres, that is to say fibres that can break under the influence of mechanical forces, such fibres actually break during the extrusion process. This has an adverse effect on the mechanical properties of the moulded article to be made from the polymer composition. This is true both for a method in which both the polymer of the polymer composition and the fibres are separately fed to the extruder, and also for a method in which a fibre-filled polymer composition is fed to the extruder to be processed into a moulded article. In a tensile test (according to ISO 527) brittle fibres generally have an elongation at break of less than 10%. Long fibres usually have a length of 0.8-100 mm.

The object of the invention therefore is to provide a method in which there is much less breakage of the brittle fibres during the extrusion, so that good mechanical properties of the extruded moulded article are obtained. In the prior art there have been attempts to find such a solution, which has resulted in proposals to adapt the screw configuration of the extruder, but so far this has not led to a satisfactory result.

The present invention relates to a method for extruding a polymer composition filled with brittle fibres, with the aid of an extruder to obtain a moulded article, which is characterised in that the brittle fibres have a length of 0.8-100 mm and that the polymer composition first of all is preheated to a temperature of at least 80°C before the polymer composition is fed to the extruder and is extruded. Preferably, this preheat-temperature is at least 100°C. This ensures that minimal mechanical loading of the brittle fibres suffices to reach the extrusion conditions in the extruder, in particular the extrusion temperature, so that fibre breakage during the extrusion is minimised, resulting in an extruded moulded article in which the fibre length corresponds much more to the original length of the fibres as they are fed to the extruder. In itself the installation to be used to heat up the fibre-filled polymer composition is not critical. If preheating takes place to a temperature below the softening temperature of the polymer composition, this preheating can be obtained by both mechanical and, preferably, non-mechanical processing of the polymer composition. If preheating is carried out to above the softening temperature, then heating by mechanical processing (an operation in which heating takes place by exerting shear forces) should be avoided. Use can be made of for example a hopper drier (a silo in which the material is heated up with a gas, such as air or nitrogen), or a drying stove.

When use is made of a semi-crystalline polymer in the polymer composition, the polymer composition is preferably heated up so that a temperature is reached that is 5-50°C, preferably 10-45°C, below the melting temperature of the polymer composition. The melting temperature is here understood to be the peak in the DSC thermogram (DSC = differential scanning calorimetry), measured at a heating-up rate of 10°C/minute. When use is made of an amorphous polymer in the polymer composition, the polymer composition is preferably heated up so that a temperature is reached that is 5-50°C, preferably 10-45°C, below the softening temperature of the polymer composition. This softening temperature is measured via DMTA (dynamic-mechanical thermal analysis; ASTM D5279). One skilled in the art is simply able to establish this heating-up temperature experimentally, the determining factor being the handling properties of the heated mass (the material should not yet stick, for example). Surprisingly, it has been found that such a heating-up temperature does not affect either the flow properties of the heated-up polymer composition or the processability during feeding to and processing in the extruder.

The invention is of special interest for that polymer composition in which the brittle fibres are glass fibres or carbon fibres. Such fibres are particularly sensitive to breakage under mechanical load. Fibres in which the effect of the invention is particularly evident are long fibres, which are fibres which usually have a length of 0.8-100 mm, preferably a length of 1-50 mm, more preferred a length of 2-25 mm.

The method according to the invention is also well suitable for the joint extrusion of a thermoplastic and the fibre-filled polymer composition, for example in a situation in which the polymer composition is fed to the extruder as a so-called "masterbatch". This can take place in different ways, at least if it is ensured that the preheated polymer composition is exposed to a minimal mechanical load also during the joint extrusion. This can be achieved by feeding the thermoplastic to the first section of the extruder and heating it up in the extruder until a melt is obtained, after which the preheated fibre-filled polymer composition is fed via a side feed inlet on the extruder. Another possibility is to heat up the thermoplastic in a separate heating unit and then feed it preheated, optionally as a melt (for example via a separate extruder), to the extruder, simultaneously with the preheated polymer composition.

Preferably the polymer composition and the thermoplastic are based on the same polymer or on polymers that are compatible, optionally with the aid of a compatibiliser.

The polymer in the polymer composition and in the thermoplastic is in principle chosen from the collection of (semi-)crystalline and amorphous polymers. In particular the polymer in the polymer composition is a polyolefin, a polyester or a nylon, both in the form of a homopolymer and in the form of a copolymer. One skilled in the art is familiar with such polymers.

The polymer composition is based in particular on a polyolefin; if, as described above, a thermoplastic is added to the fibre-filled polymer composition, the thermoplastic, too, is preferably a polyolefin. In both cases it is preferred for the polyolefin to be a polyethylene or a polypropylene. For polyethylene as well as for polypropylene this can be both homopolymer and (random) copolymer. The method according to the invention is of special interest when the brittle-fibre-filled polymer composition is fed to the extruder in the form of a granulate with the brittle fibres being essentially oriented in the longitudinal direction of the granulate and having the length or almost the length of the granulate. This then relates to both granulate in which almost every fibre is separately surrounded by polymer and to, which is preferred, a granulate in which a bundle of the brittle fibres is encapsulated in a polymeric coat, as well as to mixed forms of these. Mechanical processing of such a granulate according to the state-of-the-art results in a dramatic reduction in fibre length, resulting in unsatisfactory mechanical properties of the final moulded article. Another suitable embodiment of the invention is when use or reuse is made of (glass-) mat reinforced thermoplastics; this usually relates to the recycling of waste of such products. In such products, too, long, brittle fibres are present, mostly in the form of glass or carbon fibres.

Because the polymer composition has already been strongly heated up before it is fed to the extruder, the extruder can also be of a simple nature. This is understood to mean that in the extruder virtually no means need to be present that exert a strong mechanical load on the polymer composition: there should only be means to heat the preheated polymer composition to the extrusion temperature and means to achieve a good dispersion of the fibres in the extrudate, and thus in the moulded article. Where this specification uses the term "extruder", this is also intended to cover all other equipment used to mould a melted polymer composition; this includes moulding by means of injection moulding, extrusion/compression moulding and injection/compression moulding. The advantages of the method according to the invention are manifested in a strong decrease in fibre breakage and improved mechanical properties, including the impact strength (Izod, measured according to ISO 180/4A) and the puncture energy (measured according to ISO 6603). The puncture energy value (PEV) of an extruded moulded article on the basis of glassfibre-filled polypropylene and made using the method of the present invention, surprisingly has a value of at least 7.8 KJ/m, which is higher than in the state of the art. More generally, it has been found that the PEV of an extruded moulded article obtained according to the method according to the invention is at least 7.5% higher than the corresponding value for an extruded moulded article obtained without preheating of the polymer composition. More particular, said PEV is at least 15% higher.

Besides the above-described essential elements that should be present in the polymer composition and/or in the thermoplastic, all kinds of ingredients can be present in the polymer materials that influence the properties of the final composition and the moulded article to be made therefrom. Examples are the presence of anti-oxidants, fillers, colourants, UV stabilisers. This sort of ingredients are known to one skilled in the art and are often used by him.

The invention also relates to a moulded article obtainable with the method according to the invention. Moulded articles find application in the automotive industry, in building construction, etc. Examples are rigid and impact- resistant (structural) car components, such as splash-shields. The invention will be explained on the basis of the following Examples and comparative experiments, without this being intended to limit the invention.

Examples l-IV/comparative experiments A-D

Glass fibre-reinforced polypropylene granulate, Stamax(®) XP031 and Stamax (®) XP040 from DSM (30% glass; granulate length = 12 mm = glass fibre length; diameter of the glass fibre 20 and 25 μm, respectively; granulate diameter = 3 mm) was heated in a Kannegieser plasticizing unit (D = 90 mm, L/D = 26) to a temperature of 240°C with different cycle times; the exiting melt strip was extruded in hot condition in a Hoesch moulding unit at a moulding temperature of 50°C to form a square plate of 400 x 400 mm, with a thickness of 3.2 mm.

The plates were visually assessed for glass fibre dispersion with the aid of X-ray pictures. In addition the following mechanical properties were determined:

- Puncture energy (PEV): ISO 6603/2;

- Notched impact value (Izod): ISO 180/4A;

- Tensile strength (TS): ISO 527/1 B; - E-modulus (EM): ISO 527/1 B.

In the Examples l-IV the granulate was preheated to 140°C in a W 300 Somos Hopper preheater before it was added to the plasticizing unit; in the comparative experiments A-D the granulate was added directly to the plasticizing unit at a temperature of 20°C. The degree of dispersion of the glass fibres that was obtained was established visually, the measure of dispersion increasing from a rating of (0) to a rating of (10).

The results are shown in Tables I and II (Granulate A = Stamax® XP031 Granulate B = Stamax ® XP040). The Izod value presented in Table II is the value for the "parallel" Izod. Table 1

Influence of preheating on dispersion and plasticizing behaviour

The degree of dispersion directly affects the surface quality of moulded articles obtained: the better the degree of dispersion, the smoother the surface, and the lower the extent to which fibres are visible at the surface of the moulded article.

Table

Influence of preheating on mechanical properties

From Tables I and II it can be concluded that moulded articles made using a method according to the invention show better mechanical properties; this is true in particular for the PEV and the IZOD. This result is attributable to the strongly reduced breakage of the glass fibres during processing into moulded articles. This reduced breakage could also be observed in the X-ray pictures.

Claims

1. Method for extruding a polymer composition filled with brittle fibres, with the aid of an extruder to obtain a moulded article, characterised in that the brittle fibres have a length of 0.8-100 mm and that the polymer composition is first of all preheated to a temperature of at least 80°C before the polymer composition is fed to the extruder and is extruded.

2. Method according to claim 1 , characterised in that the preheating gives the polymer composition a temperature that is 5-50°C below the melting temperature or the softening temperature of the polymer in the polymer composition.

3. Method according to either of claims 1-2, characterised in that the brittle fibres are glass fibres or carbon fibres.

4. Method according to any one of claims 1-3, characterised in that in the extruder both a preheated or even melted thermoplastic as well as the preheated, brittle-fibre-filled polymer composition are mixed with each other and thereafter jointly extruded to form a moulded article.

5. Method according to claim 4, characterised in that the polymer composition and the thermoplastic are based on the same polymer or on polymers that are compatible with each other.

6. Method according to any one of claims 1-5, characterised in that the fibre-filled polymer composition is based on a polyolefin, on a polyester or on a nylon.

7. Method according to either of claims 5-6, characterised in that the polymer composition is based on a polyolefin.

8. Method according to either of claims 6-7, characterised in that the polyolefin is a polyethylene or a polypropylene.

9. Method according to any one of claims 1-8, characterised in that the brittle-fibre-filled polymer composition is fed to the extruder in the form of a granulate, with the brittle fibres being essentially oriented in the longitudinal direction of the granulate and having the length or almost the length of the granulate.

10. Method according to claim 9, characterised in that in the granulate a bundle of the brittle fibres is encapsulated in a polymeric coat.

11. Method according to any one of claims 1-10, characterised in that the fibres have a length of 1-50 mm.

12. Extruded moulded article obtainable via a method according to any one of claims 1-11.

13. Extruded moulded article on the basis of a polypropylene and reinforced with glass fibres, characterised in that the moulded article has a PEV of at least 7.8 KJ/m.