ZELLNER LINDA (SE)
JOHANSSON PETER (SE)
| US20080125532A1 | 2008-05-29 | |||
| US20100311886A1 | 2010-12-09 | |||
| US20130012631A1 | 2013-01-10 | |||
| CN103965594A | 2014-08-06 |
PUCHALSKI, M. ET AL.: "Investigation of the Influence of PLA Molecular Structure on the Crystalline Forms (alfa'and alfa) and Mechanical Properties of Wet Spinning Fibres", POLYMERS, vol. 9, no. 12, January 2017 (2017-01-01), pages 3, XP055562702, ISSN: 2073-4360
CAPA 6500, 6 August 2018 (2018-08-06), Retrieved from the Internet
HUANG, J. ET AL.: "Control of carbon nanotubes at the interface of a co-continuous immiscible polymer blend to fabricate conductive composites with ultralow percolation thresholds", CARBON, vol. 73, July 2014 (2014-07-01), pages 267 - 274, XP028836240, ISSN: 0008-6223
NAVARRO-BAENA, I. ET AL.: "Design of biodegradable blends based on PLA and PCL: From morphological, thermal and mechanical studies to shape memory behavior", POLYMER DEGRADATION AND STABILITY, vol. 132, October 2016 (2016-10-01), pages 97 - 108, XP029734326, ISSN: 0141-3910
| CLAIMS 1. A flame retarded, low smoke thermoplastic composition, wherein said composition is a physical blend comprising; a) 20 - 60 % by weight of polycaprolactone having an weight average molecular weight of at least 50.000, b) 20 - 50% by weight of polylactide having a weight average molecular weight of at least 100.000, c) 20 - 40% by weight of aluminium trihydrate having an average particle size in the range 0.2 pm and 20 pm. 2. A flame retarded, low smoke thermoplastic composition according to claim 1 , wherein the composition further comprises a compound selected from the group consisting of; octadecanoic acid, ethylene bis stearamide, polytetrafluoroethylene and calcium carbonate. 3. A flame retarded, low smoke thermoplastic composition according to claim 2, wherein the octadecanoic acid is present in the composition to an amount in the range 0.1 - 1.0% by weight of the total composition. 4. A flame retarded, low smoke thermoplastic composition according to claim 2, wherein the ethylene bis stearamide is present in the composition to amount in the range 0.1 - 1.0% by weight of the total composition. 5. A flame retarded, low smoke thermoplastic composition according to claim 2, wherein the polytetrafluoroethylene is present in the composition to an amount in the range 0.05 - 0.3% by weight of the total composition. 6. A flame retarded, low smoke thermoplastic composition according to claim 2, wherein the calcium carbonate is present to an amount in the range 0.5 - 5% by weight of the total composition. 7. A flame retarded, low smoke thermoplastic composition according to claim 1 , wherein the composition further comprises 10 - 20% by weight of polycaprolactone having an weight average molecular weight in the range 25.000 - 50.000. 8. A process for producing a flame retarded, low smoke thermoplastic composition, wherein the process comprises the steps; a) 40 - 70 parts by weight of polycaprolactone with an average weight molecular weight in the range 25.000 - 120.000 is compounded with 30 - 60 parts by weight of aluminium trihydrate, b) 55 - 70 parts by weight of the resulting compound of step a) is compounded with 30 - 45 parts by weight of polylactide having an average weight molecular weight of at least 100.000, and optionally, an additional 5 - 30 parts by weight of polycaprolactone with an average weight molecular weight in the range 50.000 - 120.000. 9. A process according to claim 8 wherein 0.05 - 0.3 parts by weight of polytetrafluoroethylene is added in step a) or step b). 10. A process according to claim 8, wherein 0.5 - 5 parts by weight of calcium carbonate is added in step a) or step b). |
The present invention refers to a flame retarded low smoke thermoplastic composition.
Most thermoplastic materials, with some exceptions, do present a fire hazard and many also produce large amounts of smoke when burning. Polyvinylchloride is a material that in itself is a halogen and therefore self-extinguish. However, when fuelled by other fire, hydrochloric acid is produced which is a great problem. In some applications polyvinylchloride need to be plasticized in order to obtain desired mechanical properties. The plasticizer itself will fuel a fire and render the composition fire hazardous.
Today many seek for thermoplastic materials that are at least partly from a renewable, non-fossil source. One such material is polylactide, also known as polylactic acid or PLA. This material is readily available in large quantities as a material from renewable sources such as for example though fermentation. This material is however rather brittle and needs to be plasticized in most practical uses. It is also rather flammable. One known composition is to produce a physical blend or compound between polycaprolactone and polylactide. Although the mechanical properties are vastly improved, the material is still flammable.
We have surprisingly found, through elaborate experimentation, a composition that fulfil several requirement on fire proof and low smoke thermoplastic materials and still be free from hazardous and undesired materials such as halogens and phosphates. The invention relates to a flame retarded, low smoke thermoplastic composition. The invention is characterised in that said composition is a physical blend comprising;
a) 20 - 60 % by weight of polycaprolactone having an weight average molecular weight of at least 50.000,
b) 20 - 50% by weight of polylactide having a weight average molecular weight of at least
100.000, c) 20 - 40% by weight of aluminium trihydrate having an average particle size in the range 0.2 pm and 20 pm.
In a preferred embodiment of the invention, the composition is a compounded blend comprising; a) 30 - 40 % by weight of polycaprolactone having an weight average molecular weight of at least 50.000,
b) 30 - 40% by weight of polylactide having a weight average molecular weight of at least
100.000,
c) 25 - 35% by weight of aluminium trihydrate having an average particle size in the range 5 pm and 15 pm.
In different embodiments of the invention, the composition further comprises a further compound selected from the group consisting of; octadecanoic acid, ethylene bis stearamide, polytetrafluoroethylene, calcium stearate, talcum and calcium carbonate. Octadecanoic acid, calcium stearate and ethylene bis stearamide is foremost used to improve processability such melt flow rate, flow and slip properties and may also further improve dispersion of the different components. Such further compound is in these cases added in amounts of 0.1 - 1.0% by weight of the total composition.
Polytetrafluoroethylene is typically added in thin goods materials such as films and foils and will reduce dripping. In such applications, it may show advantageous to add polytetrafluoroethylene to an amount in the range 0.05 - 0.3% by weight of the total composition.
Mechanical properties such a stiffness can be improved by adding 0.5 - 5% of calcium carbonate and/or talcum to the total composition.
In one special embodiment of the invention, the composition further comprises 10 - 20% by weight of polycaprolactone having a weight average molecular weight in the range 30.000 - 50.000. In this embodiment 25 - 35 % by weight of the 25.000 - 50.000 mw polycaprolactone is compounded with 65 - 75% by weight of aluminium trihydrate. This compound is then used a master batch to carry the aluminium trihydrate into the final composition comprising polycaprolactone with a weight average molecular weight above 50.000 and polylactide with a weight average molecular weight of above 100.000.
The invention also relates to a process for producing a flame retarded, low smoke
thermoplastic composition. The invention is characterised in that the process comprises the steps;
a) 40 - 70 parts by weight of polycaprolactone with an average weight molecular weight in the range 25.000 - 120.000 is compounded with 30 - 60 parts by weight of aluminium trihydrate,
b) 55 - 70 parts by weight of the resulting compound of step a) is compounded with 30 - 45 parts by weight of polylactide having an average weight molecular weight of at least 100.000, and optionally, an additional 5 - 30 parts by weight of polycaprolactone with an average weight molecular weight in the range 50.000 - 120.000.
It has shown during experimentation that polylactides are sensitive to humid conditions where they will break down though hydrolyzation, a process that will accelerate due to the by-products forming. It is believed that aluminium trihydrate could initiate such a hydrolyzation. It has accordingly been found that the useful life of a compound described in the present invention will be radically extended by introducing the aluminium trihydrate in the polycaprolactone. The hydrophobic caprolactone will provide a protective matrix once compounded with the polylactide. Dispersion of the aluminium hydrate in the final product will also be improved through the process described above. A good dispersion is essential, especially in sheet, film and foil products as it has a great impact on the fire resistance of the final product. In cases where the dispersion is inferior, more aluminium hydrate will have to be added to reach the same level of fire resistance. This will have an adverse effect on the mechanical properties of the final product.
According to one embodiment of the invention 0.05 - 0.3 parts by weight of
polytetrafluoroethylene is added in step a) or step b). This is useful in thinner materials like sheet, film and foil as it will reduce dripping when the foil is exposed to open flame. According to another embodiment of the invention 0.5 - 5 parts by weight of calcium carbonate is added in step a) or step b). This is useful when more rigid materials are required.
Embodiment examples
A set of samples comprising polycaprolactone, polylactide and different fire retardants where compounded in formulations as specified in table 1. A worst case was selected by making foils with 0.5 mm thickness. Test samples with the dimension 40 x 100 mm where arranged on a wire and then subjected to open flame from a gas burner for fifteen seconds in accordance with DIN 4102. The results of the experiments are presented in table 2.
Table 1
PLA = polylactide
PCL = polycaprolactone
ATH = aluminium trihydrate
UltraCarb = hydromagnesite & huntite
Exolit = phosphinate Table 2; results
Table 3; results, mechanical properties.
It shows that tensile strength and elongation at yield and at break is within acceptable parameters and that these further can be varied in order to meet customer requirements with maintained fire retardant properties as shown in table 2.