COMPOSITIONS OF THERMOPLASTIC POLYMER AND SMELT

Abstract: A composition of smelt and a thermoplastic polymer, and uses thereof, are disclosed. Smelt is a by-product of the pulp and paper industry.

Description: COMPOSITIONS OF THERMOPLASTIC POLYMER AND SMELT The present invention relates to polymer compositions, and in particular to compositions of thermoplastic polymer with a by-product of a pulp and paper mill that is known in the trade as smelt. Smelt may also be referred to in the trade as "top ash", "precipitator ash" or "recovery boiler residues", all of which are referred to herein as smelt. One of the by-products of a pulp and paper mill is a mixture of inorganic chemicals that are primarily salts of sodium. The by-product is known as smelt, as discussed above, and is regarded as an environmentally hazardous mixture of inorganic chemicals. Typical examples of such chemicals are sodium carbonate, sodium sulphide, sodium sulphate and sodium chloride. Salts of potassium and/or magnesium may also be present. The by-product, that is smelt, is typically disposed of in a landfill and environmentally more acceptable methods of disposal of smelt would be worthwhile. In a landfill, or in other locations, smelt will come in contact with moisture. Such moisture results in chemical reactions, such as the alkaline hydrolysis of the sodium and potassium carbonate and sodium sulphide. The latter is frequently accompanied by the generation of gaseous hydrogen sulphide. Chemical substances that are alkaline in nature, when mixed into at least some polymers, tend to adversely affect the physical properties of the polymer. In particular, depending on the type of polymer, alkaline substances have a tendency to cause degradation of the polymer. Polymer compositions of plastics with smelt as a filler, a foaming agent or other component, have now been found, and such compositions have useful properties. Accordingly, the present invention provides a composition of polymer and smelt, especially a composition of thermoplastic polymer and smelt. In preferred embodiments of the composition of the present invention, the smelt acts as a filler, a foaming agent and/or as a stabilizer for the polymer. In another embodiment, the polymer is a thermoplastic polymer. In further embodiments of the invention, the polymer is selected from polyolefin, polyamide, polyurethane, polyester, polycarbonate, acrylic polymers and elastomers. In a still further embodiment, the composition additionally contains a mono- or polyfunctional organic acid. The present invention relates to the use of smelt in polymer compositions. As used herein, "smelt" refers to an incinerated pulping and bleaching liquor from the pulp and paper industry, that has been concentrated by thermal evaporation followed by recovery boiler combustion. In particular, the liquor is from so-called Chemi-Thermo-Mechanical Pulp (CTMP) and peroxide bleaching. The smelt collected as solid plaques at the bottom of the recovery boiler (which plaques are ground prior to incroporation in a thermoplastic polymer composition) tends to be grey/pink in colour when dry and grey/blue in colour in the presence of water. The precipitator ash, or top ash, collected at the top of the boiler is a very fine, white color powder, generally having a particle size less than 100 mesh. In examples of smelt, the composition may be as follows: sodium carbonate 30 - 99 percent by weight, potassium carbonate .01 - 10 percent by weight, sodium sulphate 0.5 - 30 percent, sodium sulphide 0.01 - 20 percent by weight, sodium chloride 0 - 5 percent by weight and water-insoluble chemicals, including silicates, oxides or organic material 0 - 40 percent by weight, with the balance typically being other chemicals, including magnesium compounds. However, it will be understood that the composition of smelt from a particular pulp and paper mill will vary and further variations may be expected from one mill to another, especially where the mills are operated by different companies or utilize different procedures. The polymer of the polymer composition is a thermoplastic polymer. Examples of such polymers include polymers or copolymers of olefin monomers including ethylene, propylene, vinyl chloride, styrene, butylene, isobutylene, and vinyl acetate. Other polyolefins may be used. In addition, the thermoplastic polymer may be a copolymer of acrylic monomers such as acrylic acid, and ionomers thereof, including sodium acrylate and acrylic esters, for example, methyl and ethyl acrylate, methyl or ethyl methacrylate, and ethylene/acrylic acid (EAA) copolymers. Copolymers of acrylic monomers with olefins and vinyl monomers arc also included, for example, ethylene-acrylic acid copolymer, ethylene- methyl acrylate copolymer, acrylonitrile-butadiene-styrene polymers. Elastomeric copolymers or terpolymers of olefins may be used, such as ethylene-propylene elastomer, ethylene-propylene-diene (for example, butadiene) elastomer, for example, EPDM polymers. In addition the thermplastic polymer may be a polycondensation product such as polyamides, polyurethanes, polyesters and polycarbonates. Examples of polyurethanes are condensation products of polyisocyanates and a hydroxyl-containing material, including polymers of hexamethylene diisocyanate and 1 ,4-butanediol. Examples of polyamides are polymers of lactams and amino carboxylic acids and polymers of dicarboxylic acids and diamines, including nylon 6, nylon 11 , nylon 12, nylon 6,6, nylon 6,10, nylon 12, 12 and the like. Examples of polyesters are polymers of dicarboxylic acids and dihydroxy compounds including polyethylene terephthalate and polybutylene terephthalate. The polymer composition may contain one polymer or a mixture of two or more polymers as the final application requires. The polymers are of a molecular weight that is typical of polymers that are used in melt processing apparatus. The amount of smelt that may be incorporated into the polymer may be varied over a wide range. For instance, the amount of smelt may be up to 90 percent by weight of the polymer. The upper limit on the amount of smelt in the polymer is primarily governed by the ability to incorporate the smelt into the polymer in melt processing apparatus. For example, the amount of smelt may be in the range of 1 - 90 percent by weight, and in preferred embodiments is in the range of 10 - 75 percent by weight and especially in the range of 25 - 60 percent by weight. Other additives may in incorporated into the polymer in addition to the smelt. For instance, the polymer may contain up to about 50 percent, preferably up to 36 percent and especially up to about 25 percent by weight of other additives such as organic acids as well as plastifiers, stabilizers, pigments, and fillers or colorants. The organic acids may be mono or polyfunctional organic acids having one, two or three carboxylic acid functional groups. Examples of such organic acids include oxalic acid, tartaric acid, citric acid, malic acid, maleic acid, malonic acid and succinic acid. When the smelt is used for foaming, acid has to be added to the compound. This amount of acid depends on the type of the acid and can be up to 50 percent by weight. As noted above, smelt is a by-product of the pulp and paper industry, and is regarded as being primarily a mixture of inorganic chemicals. Typical chemicals found in smelt include sodium carbonate, potassium carbonate, sodium sulphate, sodium sulphide, sodium chloride as well as other water-insoluble chemicals for example, silicates and oxides. Smelt may also include organic carbon compounds. Due to its particular chemical composition, the smelt powder is believed to be useful as a filler without having any inconvenience generated by the alkaline character of it. Moreover, the presence of the sulfide anion provides a stabilizing effect to many polymers, in the same manner as different hydrides do. In addition, the carbonate content of the smelt mixed together in plastics with a solid organic acid acts as a foaming agent by generating carbon dioxide during thermal processing. In an embodiment of the invention, the composition of smelt is as follows: sodium carbonate 63 - 91 percent by weight, potassium carbonate 1 - 5 percent by weight, sodium sulphate 4 - 10 percent by weight, sodium sulphide 0.01 - 12 percent by weight, sodium chloride 0.09 - 2 percent by weight and water insoluble chemicals 3.9 - 8 percent by weight. In another embodiment, smelt has a composition of sodium carbonate 41 - 99 percent by weight, potassium carbonate 0.01 - 3 percent by weight, sodium sulphate 0.98 - 20 percent by weight, sodium sulphide 0.01 - 14 percent by weight, sodium chloride 0 - 2 percent by weight and water insoluble chemicals 0 - 20 percent by weight. An approximate composition of another example of smelt is by weight, sodium carbonate 75 - 85 percent, sodium sulphate 4 -8 percent, sodium sulphide 8 - 12 percent, sodium chloride 0.5 - 2 percent and water-insoluble matter 5 - 10 percent. Any remaining amounts are typically other chemicals. Smelt may have a wide range of particle sizes, for example, in the range of 0.0005 mm to 1.00 mm, preferably in the range of 0.001 - 0.01 mm. Smelt may be incorporated into the thermoplastic polymer by techniques known in the art for incorporating filler or other materials into thermoplastic polymers. In particular, the thermoplastic polymer and the smelt may be fed to an extruder that is operated at temperatures above the melting point of the thermpolastic polymer. The smelt is compounded into the polymer using such equipment. Alternatively, smelt may be compounded into the thermoplastic polymer so as to form a concentrate of the smelt within the polymer. The concentrate may then be fed to further processing equipment, blended with additional polymer and extruded in order to fabricate an article. Premixing operations may also be used for example, using internal mixing apparatus, examples of which are Banbury and Moriyama mixers. So-called salt and pepper blends may be used. It is understood that the thermoplastic polymer used to form such a concentrate need not be the same thermoplastic polymer as used to form the article, although the two thermoplastics should be compatible. Compatibilizers may be used, if necessary. In another embodiment, the smelt may be compounded into the thermoplastic polymer and fabricated directly into an article without forming a concentrate or forming a compounded composition of polymer and concentrate which is subsequently fabricated into an article. Compositions of smelt and thermoplastic polymer may be fabricated into articles in a wide variety of melt processing equipment used for the processing of thermoplastic polymers. Such equipment includes extruders, compounding equipment, moulding equipment, sheet forming equipment and film blowing equipment. The smelt may be used as a filler for the thermoplastic polymer. Alternatively, the smelt may be used as a foaming agent for the thermoplastic polymer. In the latter embodiment, acidic components may be blended with the smelt in order to generate gas for the foaming of the polymer. Typical acidic components have been described above. Articles from the compositions of polymers and smelt may be used as, for example, plastic wood, for example, plastic lumber, skids, malting, bumpers, livestock flooring, garbage bags, fencing parts, or in marine applications, for example, bumper dock decks, traffic cones and the like. The present invention is illustrated by the following examples. EXAMPLE I The following compositions were prepared: Percent by Weight A Polypropylene 100.0 B Polypropylene 80.0 Smelt 20.0 C Polypropylene 79.5 Smelt 20.0 lrganox™ 1010 0.5 D Polypropylene 79.0 Smelt 20.0 Tartaric Acid 1.0 E Polyethylene 100.0 F Polyethylene 80.0 Smelt 20.0 G. Polyethylene 79.5 Smelt 20.0 lrganox™ 1010 0.5 H Polyethylene 79.0 Smelt 20.0 Tartaric Acid 1.0 1 Polyethylene 80.0 Calcium Carbonate SuperFlex™ 200 20.0 J Polyethylene 80.0 Talc 20.0 The polypropylene was homopolymer polypropylene obtained from Amoco Corporation under the code FO2186. The polyethylene was DOWLEX™ linear low density polyethylene obtained from The Dow Chemical Company under the code 25355N. The smelt used was a Precipitator ash of the following composition: Percent by Wt. Sodium carbonate 74.30 Sodium sulphate 9.60 Sodium sulfide 2.90 Sodium chloride 0.08 Water insolubles 10.00 Other components (oxides, silicates, 3.12 magnesium and potassium salts) Samples of tensile bars were moulded on moulding apparatus using standard injection moulding procedures and temperatures appropriate to the polymer. The samples thus obtained were maintained at a constant temperature, and tensile strength and elongation measurements were performed on the samples over a period of days, using the procedures of ASTM D-638. The results obtained are given in Tables 1-4. TABLE 1 Polypropylene/Smelt molded bars aged at 130°C Composition Tensile Strength (psi) Elongation ( percent) Day 0 Day 20 Day 0 Day 20 A 6400 6380 7.0 7.0 B 4900 5800 8.0 5.5 C 5350 6000 6.0 5.0 D 5600 5900 8.0 4.0 TABLE 2 Polypropylene/Smelt molded bars aαed at 130°C Composition Tensile Strength (psi) Elongation ( percent) Day O Day 20 Day 0 Day 20 E 4000 1520 180.00 1.0 F 3550 2200 11.0 2.0 G 3700 4600 11.0 6.0 H 3700 4600 12.0 5.5 TABLE 3 Polvpropylene/Smelt molded bars aαed at 105°C and 23°C Composition Tensile Strength (psi) Elongation ( percent) Temperature (°C) Day O Day 40 Day O Day 40 B 5550 5160 6.3 6.4 105°C B 5580 5496 6.6 6.4 23°C TABLE 4 Polyethylene based Smelt. Calcium Carbonate and Talc compounds aged at 130°C Composition Tensile Strength (psi) Elongation ( percent) Day O Day 20 Day O Day 20 F 3550 2200 11.0 2.0 I 3800 2100 85.0 1.0 J 4300 4900 7.0 4.0 Table 1 shows that thermo-oxidative stability of the polypropylene/smelt compounds, both unstabilized (B) and stabilized (C,D), is high. It is comparable with the stability of the polypropylene (A) itself. Table 2 shows the thermo-oxidative stability of the polyethylene/smelt compound. Polyethylene (E) degraded completely in 20 days at 130°C while the smelt containing compounds did not. A stabilizer/antioxidant further improves the stability of the smelt-filled polyethylene (compare G and H versus F). Table 3 shows that polypropylene/smelt composites do not degrade in forty days at 105°C. Their properties after forty days of accelerated aging are the same as the properties of the same composites kept at room temperatures. Table 4 shows that the polyethylene/calcium carbonate composition degrades completely in 20 days at 130°C, while the polyethylene/smelt and the polyethylene/talc composites show greater thermo-oxidative stability. For the compositions F, I, J, it is to be noted that no stabilizers/antioxidants were used. EXAMPLE II The following formulations were prepared: Percent by Weight K ENGAGE ® 8200 12.5 Precipitator ash 39 Citric acid 35.2 Oil 13.3 ENGAGE © 8200 13 Precipitator ash 40 Citric acid 29 Oil 17 Stearic acid 1 The precipitator ash was dried and ground for an average particle size of 5 micrometers and was compounded by using a pilot scale internal mixer. The obtained compounds were ground, and 2 percent of each of them were mixed into virgin ENGAGE ® 8200 granules. ENGAGE ® 8200 is an ethylene/1 -octene copolymer having a rheologically significant amount of long chain branching, a melt index of about 5 g/10 minutes as measured using ASTM D 1238 (condition 190/2.16), a melt flow ration, 1 10 /1 2 of about 7.1 as measured using ASTM D 1238 (conditions 190/2.16 and 190/10, respectively), and a density of about 0.87 gm/cubic centimeter as measured using ASTM D 792. ENGAGE ® 8200 is made by and a trademark of DuPont Dow Elastomers LLC and is made by processes such as those described in United States Patents 5,272,236, 5,278,272, and 5,665,800, the disclosures of each of which is incorporated herein by reference. The resultant compositions/mixtures were injection molded by using a pilot scale injection molder; porous bars were obtained as a result of the foaming action. The porous bars were 22 percent (formulation K) and 19 percent less dense compared to a bar obtained using virgin (pure) ENGAGE ® 8200. The cut surfaces of the foamed bars presented fine pores and a uniform foam distribution. The results of tests and experiments presented in Example I show that different polymer- smelt compositions have good mechanical (tensile/elongation) properties, have good thermo-oxidative stability and are readily processable. The results of tests and experiments presented in Example II show that a fine smelt powder in combination with an organic acid foams the polymer during regular thermal processing and generates uniform, fine pores.

Claims: 1. A composition of smelt and a thermoplastic polymer. 2. A thermoplastic polymer containing smelt as a filler. 3. A thermoplastic polymer containing smelt as a foaming agent. 4. A thermoplastic polymer containing smelt as a stabilizer. 5 The composition of Claim 1 in which the composition of the smelt is as follows: sodium carbonate 30 - 99 percent by weight, potassium carbonate .01 - 10 percent by weight, sodium sulphate 0.5 - 30 percent by weight, sodium sulphide 0.01 - 20 percent by weight, sodium chloride 0 - 5 percent by weight and water-insoluble chemicals, 0 - 40 percent by weight. 6. The composition of Claim 1 in which the composition of the smelt is as follows: sodium carbonate 63 - 91 percent by weight, potassium carbonate 1 - 5 percent by weight, sodium sulphate 4 - 10 percent by weight, sodium sulphide 0.01 - 12 percent by weight, sodium chloride 0.09 - 2 percent by weight and water insoluble chemicals 3.9 - 8 percent by weight. 7. The composition of Claim 1 in which the composition of the smelt is as follows: sodium carbonate 41 - 99 percent by weight, potassium carbonate 0.01 - 3 percent by weight, sodium sulphate 0.98 - 20 percent by weight, sodium sulphide 0.01 - 14 percent by weight, sodium chloride 0 - 2 percent by weight and water insoluble chemicals 0 - 20 percent by weight. 8. A composition of any one of Claim 1 - 7 in which the smelt has a particle size of 0.0005 mm to 1.00 mm. 9. A composition of any one of Claims 1 - 7 in which the smelt has a particle size of 0.001 to 0.010 mm. 10. A composition of a thermoplastic polymer and up to 90 percent by weight of smelt. 11. The composition of Claim 10 in which there is up to 80 percent of smelt. 12. The composition of any one of Claims 1 - 11 in which the thermoplastic polymer is a polyolefin. 13. The composition of any one of Claims 1 - 11 in which the thermoplastic polymer is polyethylene, polypropylene or a copolymer of ethylene and propylene. 14. The composition of any one of Claims 1 - 11 in which the thermoplastic polymer is polyvinyl chloride. 15. The composition of any one of Claims 1 - 11 in which the thermoplastic polymer is selected from polyamide, polyurethane, polyester, polycarbonate, acrylic polymers and elastomers. 16. The composition of any one of Claims 1 - 11 in which the thermoplastic polymer is an ethylene/vinyl acetate copolymer or ethylene/acrylic acid copolymer. 17. The composition of any one of Claims 1 - 11 in which the thermoplastic polymer is an ethylene/propylene copolymer rubber or ethylene/propylene/diene copolymer elastomer. 18. The composition of any one of Claims 1 - 11 in which the thermoplastic polymer is an acrylonitrile/butadiene/styrene polymer. 19. The composition of any one of Claims 1 - 18 in which the composition further contains an organic acid, plastifier, stabilizer, additional filler, pigment and/or colorant. 20. The composition of any one of Claims 1 - 18 in which the composition further contains up to 50 percent by weight of a mono or polyfunctional organic acid. 21. The composition of any one of Claims 1-18 in which the composition contains up to 36 percent by weight of a mono- or polyfunctional organic acid. 22. The composition of Claim 19 in which the acid is selected from oxalic acid, tartaric acid, citric acid, malic acid, maleic acid, malonic acid and succinic acid. 23. A composition of thermoplastic polymer and smelt formed into an article using an extruder, compounder, moulding equipment, sheet blowing equipment or film blowing equipment. 24. Articles made from a composition of any one of Claims 1 - 24. 25. A method of forming an article, comprising forming said article from a composition of any one of Claims 1 - 24.

Inventors: MORTIMER JACQUES, TIVADAR LADISLAU A, MORTIMER, JACQUES, TIVADAR, LADISLAU, A.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1998
Main classification: C08K11
IPC codes: C08K3