Use of recycled plastics for preparing high performance composite railroad ties

A method of maintaining proper distance between railroad rails is disclosed. The method utilizes railroad ties manufactured from a composite of polystyrene and polyolefin components, preferably obtained from recycled plastics. The composite exhibits a dual phase morphology wherein the two phases, polystyrene and polyolefin, intertwine and remain continuous throughout the material.

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We claim:

1. In a method of maintaining spacing between railroad rails by attachment of said rails to at least one railroad tie, the improvement wherein:

said at least one railroad tie is formed from a plastic composite material comprising 20-50 wt % of a polystyrene component forming a first phase and 50-80 wt % of a polyolefin component forming a second phase,

wherein said polystyrene component contains at least 90 wt % polystyrene and said polyolefin component contains at least 75 wt % high density polyethylene, and

wherein said first phase and said second phase each form three dimensional networks that are integrated with one another within said composite material.

2. A method according to claim 1, wherein said composite comprises 25-45 wt % of said polystyrene component.

3. A method according to claim 1, wherein said composite comprises 30-40 wt % of said polystyrene component.

4. A method according to claim 1, wherein said polyolefin component contains at least 80 wt % high density polyethylene.

5. A method according to claim 1, wherein said polyolefin component contains at least 90 wt % high density polyethylene.

6. A method according to claim 1, wherein said polyolefin component comprises recycled polyolefin plastics.

7. A method according to claim 5, wherein said polystyrene component comprises recycled polystyrene plastics.

8. A method according to claim 1, wherein said polystyrene component comprises recycled polystyrene plastics.

9. A method according to claim 1, wherein said plastic composite material comprises 35 wt % of said polystyrene component.

10. A method according to claim 1, wherein said plastic composite material exhibits a compression modulus of at least 172,000 psi.

11. A method according to claim 1, wherein said plastic composite material exhibits a compression modulus of at least 200,000 psi.

12. A method according to claim 1, wherein said plastic composite exhibits a compression strength of at least 3000 psi.

13. A method according to claim 1, wherein said plastic composite exhibits a compression strength of at least 3500 psi.

14. A method according to claim 1, wherein said plastic composite material exhibits a compression yield stress of at least 3000 psi.

15. A method according to claim 1, wherein said plastic composite material exhibits a compression yield stress of at least 3500 psi.

16. A method according to claim 1, wherein said composite material has a coefficient of thermal expansion of less than about 6.5.times.10.sup.-5 in/in-.degree. F.

17. A method according to claim 1, wherein said composite material has a coefficient of thermal expansion of less than about 6.0.times.10.sup.-5 in/in- .degree.F.

18. A method according to claim 1, wherein said polyolefin component contains up to 25 wt % of polyvinyl chloride; middle, low and/or low linear polyethylene; polypropylene; polystyrene; polyethylene terephthalate; polyolefin copolymers; and mixtures thereof.

19. A method according to claim 1, wherein said polystyrene component contains expanded polystyrene.

20. A method according to claim 1, wherein said polystyrene component contains foamed polystyrene.

21. A method according to claim 1, wherein said at least one railroad tie is formed by:

introducing resin into an extruder, said resin comprising 20-50 wt % of a polystyrene component and 50-80 wt % of a polyolefin component, wherein the polystyrene component contains at least 90 wt % polystyrene and the polyolefin componentcontains at least 75 wt % high density polyethylene;

heating the resin within the extruder to convert the resin into a molten state;

extruding the molten material through a cooled die having at least one orifice in the shape of the cross-section of a railroad tie, wherein during passage through the cooled die an outer solid skin forms on the extruded material, said outer solidskin having a thickness sufficient to maintain the shape of the material through subsequent stages;

conveying the extruded material through subsequent cooling stages whereby the material is sufficiently cooled to permit cutting; and

cutting the extruded material into desired lengths to form composite railroad ties.

22. In a method of providing a weight bearing support surface for railroad rails by attachment of said rails to at least one railroad tie, the improvement wherein:

said at least one railroad tie is formed from a plastic composite material comprising 20-50 wt % of a polystyrene component forming a first phase and 50-80 wt % of a polyolefin component forming a second phase,

wherein said polystyrene component contains at least 90wt % polystyrene and said polyolefin component contains at least 75 wt. % high density polyethylene, and

wherein said first phase and said second phase each form three dimensional networks that are integrated with one another within said composite material.

23. A method according to claim 22, wherein said at least one railroad tie is formed by:

introducing resin into an extruder, said resin comprising 20-50 wt % of a polystyrene component and 50-80 wt % of a polyolefin component, wherein the polystyrene component contains at least 90 wt % polystyrene and the polyolefin componentcontains at least 75 wt % high density polyethylene;

heating the resin within the extruder to convert the resin into a molten state;

extruding the molten material through a cooled die having at least one orifice in the shape of the cross-section of a railroad tie, wherein during passage through the cooled die an outer solid skin forms on the extruded material, said outer solidskin having a thickness sufficient to maintain the shape of the material through subsequent stages;

conveying the extruded material through subsequent cooling stages whereby the material is sufficiently cooled to permit cutting; and

cutting the extruded material into desired lengths to form composite railroad ties.

24. In a method of maintaining spacing between railroad rails by attachment of said rails to at least one railroad tie, the improvement wherein:

said at least one railroad tie is formed by extruding a plastic melt blend containing a polystyrene component forming a first phase and a polyolefin component forming a second phase,

wherein, within said plastic melt blend, the ratio of the viscosity of the polystyrene component to the viscosity of the polyolefin component is approximately equal to the ratio of the volume of the polystyrene component to the volume of thepolyolefin component, and

wherein said first phase and said second phase each form three dimensional networks that are integrated with one another within said composite material.