Composition for application in rotomolding processes and use of the composition

Abstract

The present invention relates to a composition for application in rotomolding processes comprising a blend of linear low density polyethylene (LLDPE) in concentrations from 20 to 40% by weight and melt flow index from 1 to 4 g/10 min; high density polyethylene (HDPE) in concentrations from 20 to 40% by weight and melt flow index from 5 to 9 g/10 min; low density polyethylene (LDPE) in concentrations from 0 to 20% by weight and melt flow index from 6 to 10 g/10 min; and linear low density polyethylene (LLDPE) in concentrations from 20 to 40% by weight and melt flow index from 3 to 7 g/10 min. A composition comprising feedstock of renewable origin, as well as its use is also disclosed.

Claims

1. A composition for application in rotomolding processes, comprising: a first linear low density polyethylene (LLDPE) in concentrations from 20 to 40% by weight and melt flow index from 1 to 4 g/10 min; high density polyethylene (HDPE) in concentrations from 20 to 40% by weight and melt flow index from 5 to 9 g/10 min; low density polyethylene (LDPE) in concentrations from 0.5 to 20% by weight and melt flow index from 6 to 10 g/10 min; and a second linear low density polyethylene (LLDPE) different from the first LLDPE in concentrations from 20 to 40% by weight and melt flow index from 3 to 7 g/10 min; wherein the melt flow index (I.sub.216) is measured according to ASTM D1238.

2. The composition according to claim 1, characterized in that the first LLDPE in concentrations from 20 to 40% by weight and melt flow index from 1 to 4 g/10 min; HDPE in concentrations from 20 to 40% by weight and melt flow index from 5 to 9 g/10 min, and LDPE in concentrations from 0.5 to 20% by weight and melt flow index from 6 to 10 g/10 min derive from renewable natural source.

3. The composition according to claim 2, characterized in that the renewable natural source polyethylene is produced from natural feedstock selected from: starch, cellulose and hemicellulose contained in lignocellulosic materials, impure glycerol, residues containing lactose and/or lactates, and sugars.

4. The composition according to claim 1, characterized in that the LDPE is present in concentrations from 0.5 to 15% by weight.

5. A process of producing parts of general use or reservoir, the process comprising molding the composition as defined in claim 1.

6. The process according to claim 5, being of producing parts of general use, characterized in that the LDPE is present in concentrations between 0.5 and 15% by weight.

7. The process according to claim 5, characterized in that articles of general use are selected from kayaks, toys, marine, agricultural and automotive parts, furniture and decorative articles.

8. The process according to claim 5, being of producing a reservoir, characterized in that the LDPE is present in concentrations between 0.5 and 15% by weight.

9. The process according to claim 8, characterized in that the LDPE is present in concentrations between 0.5 and 2% by weight.

10. The process according to claim 8, characterized in that the reservoir is a tank.

11. The process according to claim 10, characterized in that the reservoir is a water tank.

12. The process according to claim 5, characterized in that it is a rotomolding process.

Description

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

(1) The present invention describes a composition comprising a blend of polyethylenes for use in rotomolding processes.

(2) The polyethylene blend used comprises polymers with different concentrations and flow rates, and can customize the physical and mechanical properties of the article produced according to the need.

(3) The composition for application in rotomolding processes comprises linear low density polyethylene (LLDPE) in concentrations from 20 to 40% by weight and melt flow index from 1 to 4 g/10 min; high density polyethylene (HDPE) in concentrations from 20 to 40% by weight and melt flow index from 5 to 9 g/10 min; low density polyethylene (LDPE) in concentrations from 0 to 20% by weight and melt flow index from 6 to 10 g/10 min; and linear low density polyethylene (LLDPE) in concentrations from 20 to 40% by weight and melt flow index from 3 to 7 g/10 min.

(4) In an embodiment of the present invention, LLDPE in concentrations from 20 to 40% by weight and melt flow index from 1 to 4 g/10 min; HDPE in concentrations from 20 to 40% by weight and melt flow index from 5 to 9 g/10 min e LDPE in concentrations from 0 to 20% by weight and melt flow index from 6 to 10 g/10 min are from renewable natural sources.

(5) To this regard, the developed composition comprising at least 50% of polyethylene resins of renewable origin is capable of meeting the specific technical requirements for rotomolded parts such as surface finish and impact strength and at the same time provide the final product with appropriate physical and aesthetic properties.

(6) Polyethylene from renewable natural source of the present invention is produced from natural feedstock, such as, for example, starch, such as corn; cellulose and hemicellulose contained in lignocellulosic materials such as leaves and bagasse, impure glycerol, such as in the saponification residue or biodiesel production processes, residues containing lactose and/or lactates, such as whey, and preferably from sugars, such as sugarcane.

(7) Polyethylene from renewable natural source maintains the same properties, performance and versatility of applications of polyethylenes of fossil origin, besides being sustainable and ecologically correct. As an example, renewable polyethylene has reduced greenhouse gas emissions—every ton of renewable polyethylene produced captures and fixes CO.sub.2 from the atmosphere, helping to reduce greenhouse gas emissions.

(8) Furthermore, polyethylene from renewable natural source is recyclable in the same recycling chain as traditional polyethylene from fossil-source. Renewable polyethylene is not biodegradable, and therefore CO.sub.2 captured by the product remains fixed throughout the life cycle of the plastic.

(9) Still, because it has the same technical properties, appearance and versatility of application of polyethylene from fossil-source, the replacement of fossil-source polyethylene with renewable polyethylene does not require investment in new machines for its application. That is, it is possible to obtain a product with similar performance to that of fossil origin which is advantageously produced from feedstock from renewable sources.

(10) The composition prepared in accordance with the present invention can be used to produce parts of general use and reservoirs. The term “general use” indicates any applications which may be produced from a blend of polyethylenes in rotomolding processes other than reservoirs, such as kayaks, toys, marine, agricultural and automotive parts, furniture and decorative articles.

(11) Furthermore, by means of rotomolding using the present polyethylene composition, reservoirs can be produced, that is, large tanks. Preferably, the reservoir is a water tank.

(12) In rotomolding processes for producing articles in general, the composition of the present invention ideally comprises from 0.5 to 15% by weight of LDPE.

(13) In processes for reservoir production, the composition of the present invention may be free of LDPE.

(14) In another embodiment, in reservoir production processes, the composition of the present invention comprises from 0.5 to 15% by weight, preferably from 0.5 to 2% by weight of LDPE.

(15) In a rotomolding process, the polymeric material is added in the rotomold mold. After the feeding, the mold is closed with the aid of clamps or screws, and then it is taken to a furnace in biaxial rotation movement. The synergistic effect between the heat received from the furnace and the biaxial movement results in uniform heating of the material inside the mold. When the softening temperature of the polymer is reached inside the mold, it begins to adhere to the surface of the mold. The material remains in the furnace for a period sufficient for the parts to be completely molded.

(16) Still in motion, the mold is withdrawn from the chamber and the cooling process begins, which may occur at ambient temperature, forced air jet and/or water spray or even more complex systems such as cooling sleeves enclosing the mold. The cooling process also has great influence on the mechanical properties of the molded part. If cooling is slow for materials such as polyethylene, there will be sufficient time for crystal growth, resulting in high rigidity parts, however with low impact strength. Conversely, quenching will cause abrupt temperature differences in the part wall, resulting in variations in the structure of the material with different levels of polymer shrinkage, which may result in warpage of the part. Cooling time depends on the following factors: Ambient temperature; Thickness of the part; Material and thickness of the mold; Air volume and speed; Mold surface characteristics; Water temperature and flow; Rate of withdrawal of air and water from the cooling station.

(17) After the mold and the part are cooled, the biaxial rotation movement ceases and the mold is driven to a demolding station. The demolding process of the polyethylene can start at a temperature of 60° C. After the part is extracted, the mold is loaded again with material and the cycle resumes.

EXAMPLES

Example 1

(18) By way of example, the composition of the present invention for the production of articles of general use comprises:

(19) TABLE-US-00001 Melt flow index Compound (g/10 min) Ratio in the blend (%) LLDPE 2.3 25 HDPE 7.0 35 LDPE 8.3 10 LLDPE 5.0 30

Example 2

(20) Still, the same composition can be prepared from renewable natural sources, obtaining results similar to polyethylene of fossil origin. In this case, the composition comprises:

(21) TABLE-US-00002 Melt flow index Compound (g/10 min) Ratio in the blend (%) Renewable % LLDPE 2.3 25 87 HDPE 7.0 35 94 LDPE 8.3 10 95 LLDPE 5.0 30 0

Example 3

(22) In addition, an example of the composition prepared according to the present invention for producing reservoirs comprises:

(23) TABLE-US-00003 Melt flow index Compound (g/10 min) Ratio in the blend (%) LLDPE 2.3 35 HDPE 7.0 25 LLDPE 5.0 40

Example 4

(24) Likewise, the composition prepared from renewable natural sources for the production of reservoirs comprises:

(25) TABLE-US-00004 Melt flow index Compound (g/10 min) Ratio in the blend (%) Renewable % LLDPE 2.3 35 87 HDPE 7.0 25 94 LLDPE 5.0 40 0

(26) In order to demonstrate that the blends of polyethylenes of renewable natural origin of the present invention exhibit very similar values of melt flow index and density of polyethylenes of fossil origin, flow rate tests were performed according to ASTM D 1238 and density according to ASTM D 792.

(27) The results for the general use composition, according to Example 2, are given below:

(28) TABLE-US-00005 Values of the present Typical Unities invention values MFI (190° C./2.16 kg) g/10 min 4.3 4.5 DE g/cm.sup.3 0.939 0.938

(29) As for the composition prepared for use in reservoirs according to Example 4, the results are as follows:

(30) TABLE-US-00006 Values of the present Typical Unities invention values MFI (190° C./2.16 kg) g/10 min 3.9 4.0 DE g/cm.sup.3 0.938 0.939

(31) While the present invention has been widely described, it is obvious to those skilled in the art that various changes and modifications may be performed to improve the design without such changes being outside the scope of the invention.