PL229859B1 - Polyolefine-based composites - Google Patents

Abstract

The subject of the application are composites containing: 50 - 90 parts by weight of ethylene and / or propylene homopolymers and / or copolymers of the mentioned olefins with one or two monomers from the C2 - C8 olefin group, 10 - 50 parts by weight of plant filler (wood flour or other fragmented trees conifers, e.g. needles or bark or energy willow) modified with liquefied amorphous, low molecular weight polyolefin microwax, 0 - 1 part by weight of UV stabilizers and / or thermal stabilizers.

Description

Description of the invention

The subject of the invention are polyolefin-based composites serving as construction materials, primarily in construction and in the automotive industry.

In the last few decades, composites obtained with the use of renewable plant materials play a fundamental role in replacing conventional polymers and polymer composites in various types of applications. This is due to, inter alia, rising prices and depletion of global resources of petrochemical raw material (oil), from which commercial large-industrial polymers are obtained. The basic benefits resulting from the development of composites with plant fillers result from their relatively low price and practically unlimited availability (renewable nature). Composites containing ingredients of plant origin usually show good performance properties, hence they have been widely used, among others, as construction materials in construction and automotive. What's more, the production of finished products from this type of materials allows the use of known and used processing technologies. The growing demand for polymer composites with plant fillers is also associated with the popularization of pro-ecological solutions aimed at minimizing the problems associated with the disposal of polymer waste. Partial replacement of the polymer matrix with plant filler thus contributes to obtaining materials with the desired functional properties with a significant reduction in raw material costs and maintaining the typical methods used in the processing of polymer materials, and at the same time does not cause problems in their disposal and recycling of products made of them after their service life. (Penczek S. et al., Polimery, 2013, 58 (11-12) 833-958, Nagarajan V. et al., ACS Sustainable Chemistry and Engineering 2013, 1 (3), 325-333, Georgopoulos, S. Th . et al., Polymer Degradation and Stability 2005, 90 (2 SPEC. ISS.), 303-312, Błędzki AK et al., Fibers and Textiles in Eastern Europe 2005, 96 (6 B), 15-22, Faruk O. et al., Macromolecular Materials and Engineering 2014, 299, 9-26, DOI: 10: 1002).

The most commonly used plant raw materials in the production of polymer composites are kenaf, sisal, jute, linen, hemp, wood flour, ram, bamboo, cotton or coconut fibers (Faruk O. et al., Progress in Polymer Science 2012, 37, 1552-1596, Nagarajan V. et al., ACS Sustainable Chemistry and Engineering 2013, 1 (3), 325-333). The availability of these raw materials largely depends on the geographic location and climatic zone. Hence, on the Polish, European and American market, wood flour plays an essential role in the development of polymer composites with plant fillers. Polymer-wood composites are usually made by extrusion; in which it is recommended to use up to about 40% by weight of the filler, and by the injection method, in which the content of wood flour is up to about 50-60% by weight. These processes are usually preceded by mixing ingredients in various types of mixers (Kuciel S. et al., Possibility of using plastic waste, Fotobit, Kraków 2001). The amount of filler used, in the range of 10-90% by weight, has a very significant influence on the properties of the produced composites (Kuciel S. et al. Chemik 2007, 4, 27, Zajchowski S. et al. Polimery 2009, 54, 674). However, with an increase in the proportion of plant filler in relation to the thermoplastic polymer matrix, the processing properties of such material deteriorate significantly; the melt flow index decreases, which results in an increase in resistance and an increase in energy consumption. Moreover, due to the fact that the filler has a different hydrophobic character than the hydrophobic matrix, it is important to use an effective method of modifying the mixed components of the composite, or more often, adding coupling agents (compatibilizers). There are many methods of surface modification of plant fillers, both chemical [Li X., Tabil L, Panigrahi S., J. Polym. Environ. 2007; 15: 25-33], for example mercerization or acetylation, as well as physical, such as plasma treatment [Thomsen AB., Thygesen A., Bohn V., et al. IND Crop Prod 2006; 24: 113-118].

In turn, the compatibilizers used to improve interfacial adhesion are, for example, silane coupling agents, polyisocyanates, anhydrides, triazine derivatives or organosilanes [Shenton mj, Stevens GC., J. Phys. D., 2001; 34: 2761-2768].

The role of the compatibilizing agent can also be performed by synthetic waxes, for example polyolefin waxes, especially those containing hydrophilic functional groups. Nhlapo et al. Published in the Journal of Applied Polymer Science, 2012, 123, 3627-3634 describes the use of functionalized paraffin waxes in low density polyethylene based composites with sisal fibers. In turn, in the publication of Korach Ł, Czaja K., Stokłosa J., (Przemysł Chemiczny 2012, 91,

PL 229 859 B1

2471-2475) describes the use of functionalized polyethylene waxes as compatibilizers of high-filling polymer-wood composites.

The most commonly used polyolefin waxes are polyethylene waxes, i.e. ethylene oligomers with an average molecular weight of up to 10,000 g / mol. Wax obtained by direct synthesis from monomer, or as a by-product in the production of polyethylene or thermal degradation of polyethylene, is used in many areas of the economy. Examples of areas of application of polyolefin wax are the production of pigments, films, composites, polymer blends, candles, printing inks, fertilizers, and is also used in woodworking or used by the electrical and cable industry [Marszałek G., Majczak R., Polyethylene waxes- preparation, modification and application, Polymers, 57, No. 9, 2012; Urbaniak W., Wasiak W., Fall J., Waxes - products of thermal degradation of waste plastics - obtaining, capabilities, and application, Archives of Waste Management and Environmental Protection, vol. 6, 71-78, 2007; Marszałek G., Zieliński J., Ciesińska W., Obtaining polyethylene waxes in the process of high and low pressure ethylene polymerization, Przemysł Chemiczny, 90/6, 2011].

The patent description CA 676 073 claims a method of obtaining high-crystalline, olefinic polymer blends with the participation of microcrystalline waxes with a melting point of 55-105 ° C.

CA 807217 claims a method for obtaining amorphous polypropylene compositions with paraffinic and / or microcrystalline waxes.

Jianli Li et al in Solar Energy Materials & Solar Cells, 2009, 93, 1761-1767 describes the use of microencapsulated paraffin in polymer-wood composites.

In turn, the publication Xian J. and Lawrence T. Drzal published in Composites: Part A, 2011, 42, 1840-1849 describes the use of paraffin wax in nanocomposites based on high-density polyethylene, and in the publication Mngomezulu ME et al. Published in Polymer Composites, 2011 , 1155-1163 describes the use of paraffin waxes as additives to phase-change materials based on high-density polyethylene with the addition of wood flour.

In the patent literature, you can find a lot of information on the use of polyolefin wax in polymer composites filled with various raw materials of plant origin.

The patent specification GB 1026495 claims a method of obtaining foamed plastics based on thermoplastic materials with the participation of blowing agents and microcrystalline polyethylene wax.

The patent description CN 103509226 claims a method of obtaining polymer-wood composites consisting of 30-35 parts by weight of high-density polyethylene, 20-25 parts by weight of PA66 perennial, 30-35 parts by weight of straw powder and other additives, including 3-5 parts by weight of polyethylene wax.

The patent description CN 103205132 claims a method of obtaining polymer composites with the use of bamboo flour and other additives, including polyethylene wax.

The patent description CN 103146214 claims a method of obtaining flame-retardant polymer-wood composites based on polyethylene, containing wood flour and other improvers / stabilizing agents, including polyethylene wax.

The patent description CN 103122112 claims a method of obtaining polymer-wood composites based on polyvinyl chloride containing, inter alia, 0.2-1 parts by weight of polyethylene wax.

The above-described applications relate to hydrophobic polyolefin waxes and their functionalized derivatives - solid, partially crystalline materials. Their synthesis is usually accompanied by the formation of a by-product, liquid or semi-liquid, amorphous, lower molecular weight product called microwax.

Only the master's thesis by Magdalena Sitko "The use of waste polyethylene microvax for the production of useful products (Silesian University of Technology, 2013) describes the use of such a raw material, which is a mixture of mainly linear hydrocarbons, with a chain length of 6 to 40 carbon atoms and a high content of double bonds, especially terminals as a substrate for the preparation of primary alkanesulfonates - potential surfactants.

The review of literature and patent data shows that the use of synthetic, amorphous, low molecular weight (molar mass up to about 500 g / mol, number of atoms) is unknown so far.

Of carbon to 40), liquid or semi-liquid micro-waxes of various viscosities, usually a waste product in the production of polymer waxes, as an additive improving the miscibility and processability of the polyolefin matrix with plant filler in polymer composites, therefore the method of obtaining such composites is not known. .

The object of the invention were composites based on high-crystalline polyolefins with a significant proportion of plant fillers and with the addition of amorphous low-molecular polyolefin microwaxes, characterized by favorable performance properties, in particular processing and mechanical properties, such as melt flow index, impact strength and relative elongation at break.

It turned out that composites containing homopolymers of ethylene and / or propylene and / or copolymers of the olefins mentioned and copolymers of these olefins with one or two monomers from the C2-C8 group of olefins, and containing a plant filler modified with a liquid, amorphous, low-molecular polyolefin microvax. processing and mechanical properties, such as melt index, Charpy impact strength, and elongation at break.

The composites of the invention include:

• 50-90 parts by weight of propylene homopolymers and / or homopolymers of ethylene and / or copolymers of the olefins mentioned and copolymers of these olefins with one or two monomers from the C2-C8 group of olefins, • 10-50 parts by weight of vegetable filler modified with a liquefied amorphous, low-molecular polyolefin microvax • 0-1 parts by weight of UV stabilizers and / or heat stabilizers.

Preferably, the composites contain wood flour and / or comminuted waste tree fragments and / or energy willow flour as plant filler.

It is advantageous if the composites contain the plant filler in the form of fine particles up to 1 mm in size.

The composites preferably contain a microwax in a ratio of 1: 6 to the amount of plant filler.

Composites based on polyolefins contain polyolefin microwax, which is a waste product obtained during the process of thermal decomposition of polyolefins. This raw material may be a promising additive for applications in polymer composites containing a significant proportion of plant fillers, replacing the previously used solid, partially crystalline, higher molecular paraffin waxes.

Composites based on polyolefins with the participation of flour from plant raw materials and amorphous, liquid micro-wax show an improvement in processing properties and selected mechanical properties, especially with a 30% share by weight of filler in the composite.

An increase in the value of the melt flow index (MFR), impact toughness, and an improvement in the elongation at static tensile were found as compared to other polymer composites and composites containing analogous, partially crystalline solid waxes.

Examples

The mass flow rate of the obtained plastics (MFR) is determined using a Zwick weight plastometer according to the PN-EN ISO 1133: 2006 standard. Tensile strength properties (tensile strength and relative elongation at break) are determined using an Instron testing machine according to PN-EN ISO 527: 1998. The impact strength (impact resistance) is tested by the Charpy method using a pendulum hammer according to ISO 13802.

Example 1 - comparative

Composite includes:

• 70 parts by weight of high-density polyethylene under the trade name Hostalen GC 7260 (density 0.96 g / cm ³ , MFR = 8.18 g / 10 minutes (190 ° C, 2.16 kg), notched Charpy impact strength 8.39 kJ / m ² , tensile strength 29.3 MPa, relative elongation at break 136.7%), 30 parts by weight of energy willow meal previously dried in a laboratory dryer at 80 ° C for 12 hours.

PL 229 859 B1

The composite has a melt index of 4.44 g / 10 minutes, and a Charpy impact strength of 3.2 kJ / m ² . The tensile strength of the composite is 31.6 MPa, and the relative elongation at break is 3.2%.

The composite with 30% by weight of plant filler shows deterioration of processing and strength properties as compared to polyethylene without the filler. There is a decrease in the value of the melt flow index, as well as the elongation at break and impact strength, which may be caused by the limited miscibility (compatibility) between the hydrophobic filler and the hydrophobic polyethylene.

Example 2 - comparative

Composite includes:

• 65 parts by weight of polyethylene under the trade name Hostalen GC 7260, • 30 parts by weight of energy willow meal previously dried in a laboratory dryer at 80 ° C for 12 hours, • 5 parts by weight (weight ratio of filler to wax is 1: 6) of wax high-density polyethylene with the trade name C120 / 800 (viscosity 750 mPas at 140 ° C, dropping point 122 ° C).

The composite has a melt flow rate of 5.03 g / 10 minutes, and an impact strength of 2.97 kJ / m ² . The tensile strength of the composite is 27.2 MPa, and the relative elongation at break is 2.1%.

The presence of polyethylene wax with a 5% weight proportion of the composite (1: 6 weight ratio of wax to filler) results in a partial improvement in processing properties compared to the corresponding properties of the composite without the addition of wax. There is a 13% increase in the value of the melt index. However, the values of impact strength, tensile strength and elongation at break value deteriorate.

P r z k ł a d 3

Composite includes:

• 65 parts by weight of polyethylene under the trade name Hostalen GC 7260, • 35 parts by weight of energy willow meal dried in a laboratory dryer at 80 ° C for 12 hours and modified with a liquid and heated to 55 ° C high-density polyethylene micro-wax (viscosity 14 mPas in temperature 60 ° C, solidification point 45 ° C) in a weight ratio of micro-wax - plant filler as 1: 6.

The composite has a melt flow index of 5.47 g / 10 minutes, and an impact strength of 4.41 kJ / m ² . The tensile strength of the composite is 26.2 MPa, and the relative elongation at break is 5.4%.

The use of polyethylene micro-wax at a weight ratio to vegetable filler of 1: 6 results in a significant improvement in processing properties, impact strength and relative elongation without significant deterioration of the tensile strength of the obtained composite compared to the corresponding properties of the composite without the addition of wax. There is a 23% increase in the value of the melt flow index, a 38% increase in the value of the impact toughness and a 69% increase in the value of the relative elongation at break. On the other hand, compared to the composite with the addition of commercial wax, there is a 9% increase in the value of the melt flow index, a 49% increase in the impact toughness value and a 157% increase in the value of the relative elongation at break. The tensile strength values are similar.

Example 4 - comparative

Composite includes:

• 60 parts by weight of polyethylene under the trade name Hostalen GC 7260, • 30 parts by weight of energy willow flour previously dried in a laboratory dryer at 80 ° C for 12 hours and 10 parts by weight correspond to (weight ratio filler - wax is 1: 3). high-density polyethylene wax under the trade name C120 / 800 (viscosity 750 mPas at 140 ° C, drop point 122 ° C).

The composite has a melt flow index of 4.79 g / 10 minutes, and an impact strength of 4.22 kJ / m ² . The tensile strength of the composite is 23.5 MPa, and the relative elongation at break is 4.4%.

PL 229 859 B1

The presence of polyethylene wax with a weight proportion of 10% (wax-filler weight ratio 1: 3) improves processing and strength properties compared to the corresponding properties of the composite without the addition of wax. There is an 8% increase in the value of the melt flow index, a 32% increase in the value of the impact toughness and a 37% increase in the value of the relative elongation at break. However, the tensile strength value (34%) deteriorated.

P r z o l a d 5

Composite includes:

• 60 parts by weight of polyethylene under the trade name Hostalen GC 7260, • 30 parts by weight of energy willow meal dried in a laboratory dryer at 80 ° C for 12 hours and then modified with high-density polyethylene microwax, heated to 55 ° C (viscosity 14 mPas at 60 ° C, solidification point 45 ° C) in a weight ratio of microwax to vegetable filler of 1: 3 (corresponding to 10 parts by weight of microvax in the composite).

The composite has a melt flow index of 5.89 g / 10 minutes, and an impact strength of 2.53 kJ / m ² . The tensile strength of the composite is 27.7 MPa, and the relative elongation at break is 3%.

The presence of polyethylene microwax with a weight ratio to the plant filler of 1: 3 causes a significant improvement in processing properties compared to the corresponding properties of the composite without the addition of wax as well as with the addition of commercial polymer wax. There is a 33% and 23% increase in the melt index, respectively. However, the addition of polyethylene micro-wax deteriorates the impact toughness both in relation to the composite without wax and with the addition of polymer wax by 21% and 40%, respectively. The tensile strength value compared to a wax-free composite drops by 12% without affecting the elongation at break value. On the other hand, compared to the composite with the addition of a suitable wax, it increases by 18%, but with a simultaneous decrease in the value of the relative elongation at break by 32%.

Example 6 - comparative

Composite includes:

50 parts by weight of polyethylene under the trade name Hostalen GC 7260, 50 parts by weight of energy willow meal previously dried in a laboratory dryer at 80 ° C for 12 hours.

The composite has a melt flow index of 2.44 g / 10 minutes, and an impact strength of 3.01 kJ / m ² . The tensile strength of the composite is 29.3 MPa, and the relative elongation at break is 1.5%.

The composite with 50% by weight of energy willow flour shows a deterioration in processing and strength properties as compared to polyethylene without a filler. The values of the melt flow index as well as the relative elongation at break and impact toughness decrease, which may be caused by the limited miscibility of the filler with polyethylene.

Example 7 - comparative

Composite includes:

• 45 parts by weight of polyethylene under the trade name Hostalen GC 7260, • 50 parts by weight of energy willow meal previously dried in a laboratory dryer at 80 ° C for 12 hours, • 5 parts by weight (weight ratio: filler - wax is 1:10) of wax high-density polyethylene with the trade name C120 / 800 (viscosity 750 mPas at 140 ° C, dropping point 122 ° C).

The composite has a melt flow index of 2.27 g / 10 minutes, and an impact strength of 2.18 kJ / m ² . The tensile strength of the composite is 25.4 MPa. a relative elongation at break 0.51%.

The presence of polyethylene wax at 5 parts by weight in the composite (weight ratio wax - filler 1:10) causes deterioration of all assessed properties, including processing properties, compared to the corresponding properties of the composite without the addition of wax.

P r z k ł a d 8

Composite includes:

• 45 parts by weight of polyethylene with the trade name Hostalen GC 7260,

50 parts by weight of energy willow meal, previously dried in a laboratory dryer at 80 ° C for 12 hours and modified with liquid, heated to 55 ° C, high-density polyethylene microwax (viscosity 14 mPas at 60 ° C, solidification point 45 ° C) in a weight ratio of micro wax - filler 1:10 (10 parts by weight of filler in the composite).

The composite has a melt flow rate of 1.63 g / 10 minutes, and an impact strength of 3.2 kJ / m ² . The tensile strength of the composite is 20 MPa, and the relative elongation at break is 0.6%.

The presence of polyethylene microwax at a weight ratio to the vegetable filler of 1:10 (10% by weight in the composite) improves the material's impact resistance and elongation at break, but deteriorates the melt flow index and tensile strength of the obtained composite compared to the corresponding properties of the composite with such the same amount of wax. There is a 47% increase in impact strength, an 18% increase in elongation at break value, with a 28% decrease in melt index and a 21% tensile strength value compared to the properties of the corresponding wax-containing composite.

Example 9 - comparative

Composite includes:

• 69.9 parts by weight of polypropylene with the trade name Moplen HP400R (MFR = 21.29 g / 10 minutes (230 ° C, 2.16 kg), Charpy notched impact strength 4.36 kJ / m ² , tensile strength 31.4 MPa, elongation at break 680%), • 30 parts by weight of wood flour (Lignocel C-120) previously dried in a laboratory dryer at 80 ° C for 12 hours, • 0.1 parts by weight of a thermal and UV stabilizer under the trade name Irganox 1010 Composite has a melt flow index of 7.63 g / 10 minutes, and a Charpy impact strength of 2.07 kJ / m ² . The tensile strength of the composite is 34.2 MPa, and the relative elongation at break is 4.6%.

The composite with 30% by weight of commercial wood flour showed a deterioration in processing and strength properties compared to polypropylene without filler. There is a decrease in the value of the melt flow index and the relative elongation at break and impact toughness, which may be caused by the limited miscibility of the plant filler with polypropylene.

P r z k ł a d 10

Composite includes:

• 64.9 parts by weight of polypropylene with the trade name Moplen HP400R, • 30 parts by weight of wood flour, previously dried in a laboratory dryer at 80 ° C for 12 hours, then modified with high-density polyethylene micro-wax heated to 55 ° C (viscosity 14 mPas at 60 ° C, solidification point 45 ° C) with a plant filler weight ratio to microwax of 1: 6 (which corresponds to 5 parts by weight of a microwax in the composite), • 0.1 parts by weight of a thermal and UV stabilizer with the trade name Irganox 1010. The composite is characterized by has a melt flow index of 12.60 g / 10 minutes, and an impact strength of 3.12 kJ / m ² . The tensile strength of the composite is 27.7 MPa, and the relative elongation at break is 7.6%.

The presence of polyethylene micro-wax with a weight ratio of microwax to vegetable filler of 1: 6 (the proportion of microwax in the composite 5 parts by weight), results in a significant improvement in processing properties, impact strength and relative elongation without significant deterioration of the tensile strength of the obtained composite compared to the corresponding properties of the composite without the addition polymer micwax. There is a 65% increase in the value of the melt flow index, a 51% increase in the value of the impact toughness and a 65% increase in the value of the elongation at break, respectively.

P r x l a d 11

Composite includes:

• 64.9 parts by weight of polypropylene with the trade name Moplen HP400R, • 30 parts by weight of wood flour, previously dried in a laboratory dryer at 80 ° C for 12 hours, and then modified with a heated to 40 ° C polypropylene microwax (viscosity 1.5 mPas in temperature 60 ° C, temperature

Solidification of 15 ° C) with a weight ratio of filler to microwax of 1: 6, which corresponds to 5 parts by weight of a microwax in the composite, 0.1 parts by weight of a heat and UV stabilizer with the trade name Irganox 1010.

The composite has a melt index of 9.44 g / 10 minutes, and impact strength

3.11 kJ / m ² . The tensile strength of the composite is 28.3 MPa, and the relative elongation at break is 7%.

The presence of polyethylene microwax at a weight ratio of microwax - vegetable filler of 1: 6 causes a significant improvement in processing properties, impact strength and relative elongation without significant deterioration of the tensile strength of the obtained composite compared to the corresponding properties of the composite without the addition of polymer microwax. There is a 23% increase in the value of the melt flow index, a 50% increase in the value of the impact toughness and a 52% increase in the value of the relative elongation at break, respectively.

Example 12 - comparative

Composite includes:

• 69.9 parts by weight of a propylene-ethylene copolymer with the trade name Moplen EP540P (MFR = 15 g / 10 minutes (230 ° C, 2.16 kg), Charpy notched impact strength 7 kJ / m ² , tensile strength 28 , 5 MPa, relative elongation at break 290%), • 30 parts by weight of wood flour (Lignocel C-120) previously dried in a laboratory dryer at 80 ° C for 12 hours,

0.1 parts by weight of a thermal and UV stabilizer under the trade name Irganox 1010. The composite has a melt flow index of 12.4 g / 10 minutes, and a Charpy impact strength of 4.08 kJ / m ² . The tensile strength of the composite is 30.8 MPa, and the relative elongation at break is 0.56%.

E xample 13 The composite contains:

• 64.9 parts by weight of a propylene-ethylene copolymer under the trade name Moplen EP540P, • 30 parts by weight of wood flour previously dried in a laboratory oven at 80 ° C for 12 hours and then modified with a heated to 45 ° C polypropylene microvax (viscosity 1.5 mPas at a temperature of 60 ° C, solidification point 15 ° C) with a plant filler weight ratio to microwax of 1: 6 (which corresponds to 5 parts by weight of a microwax in the composite), • 0.1 parts by weight of a thermal and UV stabilizer with the trade name Irganox 1010 The composite has a melt flow rate of 13.9 g / 10 minutes and toughness

5.11 kJ / m ² . The tensile strength of the composite is 28.4 MPa, and the relative elongation at break is 0.88%.

The presence of polyethylene micro-wax for modification of wood flour with a weight ratio of micro-wax to plant filler of 1: 6 (which corresponds to 5 parts by weight of microwax in the composite) results in a significant improvement in the processing properties of the material compared to the corresponding properties of the composite without the addition of the micro-wax. There is a 12% increase in the value of the melt flow index, a 25% increase in the toughness value and a 57% increase in the value of the relative elongation at break.

Claims (4)

1. Composites based on polyolefins, characterized in that they contain: • 50-90 parts by weight of propylene homopolymers and / or homopolymers of ethylene and / or copolymers of the olefins mentioned and copolymers of these olefins with one or two monomers from the C2-C8 group of olefins, • 10-50 parts by weight of vegetable filler modified with a liquefied amorphous, low-molecular polyolefin microvax • 0-1 parts by weight of UV stabilizers and / or heat stabilizers. 2. Composites according to claim A plant according to claim 1, characterized in that it comprises wood flour and / or comminuted waste tree fragments and / or energy willow flour as plant filler. PL 229 859 B1 3. Composites according to p. 2. The method of claim 1, characterized in that they contain the plant filler in the form of crushed particles with dimensions of up to 1 mm. 4. Composites according to Claim 2. A method according to claim 1, characterized in that they contain microwax in a proportion of 1: 6 to the amount of plant filler.