Integral polyethylene terephthalate grids, the method of manufacture, and uses thereof
An integral polymer grid with a plurality of interconnected, oriented polyethylene terephthalate strands and an array of openings therein is made from a polyethylene terephthalate sheet-like starting material having holes or depressions therein that form the openings when the sheet-like material is uniaxially or biaxially stretched. The grid has a higher tensile strength to weight ratio and a higher creep reduced strength to weight ratio than corresponding ratios associated with a grid made from a non-polyethylene terephthalate starting material.
1. A polymer mesh structure comprising a substantially uniplanar integral geogrid having a plurality of highly oriented strands interconnected by partially oriented junctions forming an array of openings in said geogrid, said integral geogrid formed of polyethylene terephthalate and having (a) a tensile strength per unit of cross-sectional area of from approximately 63N/mm 2 to approximately 384N/mm 2 and (b) a creep strain at 60% loading which starts out at about 0.75% and does not exceed about 1.00% after 10,000 hours loading.
2. The polymer mesh structure according to claim 1 , wherein the highly oriented polyethylene terephthalate strands have been uniaxially or biaxially stretched.
3. The polymer mesh structure according to claim 1 , wherein the polyethylene terephthalate is a homopolymer or a copolymer.
4. The polymer mesh. structure according to claim 1 , wherein the polyethylene terephthalate is selected from the group consisting of amorphous polyethylene terephthalate, crystalline polyethylene terephthalate, and polyethylene terephthalate glycol.
5. The polymer mesh structure according to claim 1 , wherein the plurality of highly oriented polyethylene terephthalate strands includes oriented transverse strands and oriented longitudinal strands interconnected by partially oriented polyethylene terephthalate junctions.
6. The polymer mesh structure according to claim 1 , wherein the integral geogrid is configured for structural or construction reinforcement purposes.
7. The polymer mesh structure according to claim 1 , wherein the plurality of highly oriented polyethylene terephthalate strands are aligned in a longitudinal array by unilateral stretching and each aligned pair of the highly oriented strands are interconnected by a partially oriented polyethylene terephthalate junction aligned in a transverse bar.
8. The polymer mesh structure according to claim 1 , wherein the polyethylene terephthalate has a creep strain at 70% loading which starts out at about 0.75% and does not exceed about 1.50% after 10,000 hours loading.
9. A starting material for making an integral polymer geogrid comprising a homogeneous polyethylene terephthalate substantially uniplanar material having holes or depressions therein that provide highly oriented polyethylene terephthalate strands interconnected by partially oriented junctions forming an array of grid openings, when the substantially uniplanar material is uniaxially or biaxially stretched,
said integral polymer geogrid having (a) a tensile strength to weight ratio of from approximately 63N/mm 2 to approximately 384N/mm 2 and (b) a creep strain at 60% loading which starts out at about 0.75% and does not exceed about 1.00% after 10,000 hours loading.
10. The starting material according to claim 9 , wherein the polyethylene terephthalate is crystalline polyethylene terephthalate.
11. The starting material according to claim 9 , wherein the substantially uniplanar starting material has an initial thickness of at least 1.4 mm.
12. The starting material according to claim 11 , wherein the substantially uniplanar starting material has an initial thickness of at least 3 mm.
13. The starting material according to claim 12 , wherein the stretched substantially uniplanar starting material exhibits a substantially linear relationship between a stretch ratio and a specific tensile strength.
14. The starting material according to claim 9 , wherein the polyethylene terephthalate has a creep strain at 70% loading which starts out at about 0.75% and does not exceed about 1.50% after 10,000 hours loading.
15. A soil construction comprising a mass of particulate material strengthened by embedding therein a polymer mesh structure as claimed in claim 1 .
16. A method of strengthening a mass of particulate material, comprising embedding in the mass of particulate material a polymer mesh structure as claimed in claim 1 .
17. A method of making a polymer mesh structure, comprising orienting a substantially uniplanar homogeneous polyethylene terephthalate starting material having holes or depressions therein into an integral geogrid having a plurality of highly oriented. polyethylene terephthalate strands interconnected by partially oriented junctions to configure the holes or depressions as mesh openings,
said integral geogrid having (a) a tensile strength per unit of cross-sectional area of from approximately 63N/mm 2 to approximately 384N/mm 2 and (b) a creep strain at 60% loading which starts out at about 0.75% and does not exceed about 1.00% after 10,000 hours loading.
18. The method according to claim 17 , wherein the substantially uniplanar polyethylene terephthalate starting material is oriented by uniaxial or biaxial stretching.
19. The method according to claim 17 , wherein the polyethylene terephthalate is crystalline polyethylene terephthalate.
20. The method according to claim 19 , wherein the substantially uniplanar polyethylene terephthalate starting material has an initial thickness of at least 3 mm.
21. The method according to claim 17 , further comprising a step of manipulating a variable associated with the polyethylene terephthalate to improve resistance of the integral geocrid geogrid to hydrolysis, the variable being selected from the group consisting of carboxyl end group, molecular weight, crystallinity, orientation, surface area, temperature, pH, and cation presence.
22. The method according to claim 17 , wherein the polyethylene terephthalate has a creep strain at 70% loading which starts out at about 0.75% and does not exceed about 1.50% after 10,000 hours loading.
23. A method of providing a stabilized soil construction, comprising:
uniazially uniaxially or biaxially stretching a crystalline polyethylene terephthalate substantially uniplanar starting material having holes or depressions therein to form an integral geogrid having a plurality of highly oriented polyethylene terephthalate strands interconnected by partially oriented junctions which define a plurality of grid openings,
said integral polymer geogrid having (a) a tensile strength per unit of cross-sectional area of from approximately 63N/mm 2 to approximately 384N/mm 2 and (b) a creep strain at 60% loading which starts out at about 0.75% and does not exceed about 1.00% after 10,000 hours loading; and
embedding the integral geogrid in a mass of particulate material.
24. The method according to claim 23 , wherein the polyethylene terephthalate has a creep strain at 70% loading which starts out at about 0.75% and does not exceed about 1.50% after 10,000 hours loading.
25. A substantially uniplanar integral geogrid formed by uniaxially or biaxially stretching and orienting a substantially uniplanar sheet-like material having an array of perforations or indentations, said substantially uniplanar integral geogrid comprising:
a plurality of interconnected, oriented strands and partially oriented junctions having an array of openings therebetween, with the substantially uniplanar sheet-like material and the substantially uniplanar integral geogrid being made of polyethylene terephthalate.
26. The substantially uniplanar integral geogrid according to claim 25, wherein the polyethylene terephthalate substantially uniplanar sheet-like material is biaxially stretched and oriented to form the polyethylene terephthalate substantially uniplanar integral geogrid having molecularly oriented longitudinal strands and molecularly oriented transverse strands interconnected by the partially oriented junctions which define generally square or rectangular grid openings.
27. The substantially uniplanar integral geogrid according to claim 25, wherein the polyethylene terephthalate is a homopolymer or a copolymer.
28. The substantially uniplanar integral geogrid according to claim 25, wherein the polyethylene terephthalate is selected from the group consisting of amorphous polyethylene terephthalate, crystalline polyethylene terephthalate, and polyethylene terephthalate glycol.
29. The substantially uniplanar integral geogrid according to claim 25, wherein the polyethylene terephthalate substantially uniplanar sheet-like material is uniaxially stretched and oriented to form a generally square or rectangular grid of substantially parallel oriented strands and a set of substantially parallel bars generally at right angles to the strands, wherein an end of each of the strands is oriented into adjacent ones of said parallel bars.
30. The substantially uniplanar integral geogrid according to claim 25, wherein the polyethylene terephthalate substantially uniplanar sheet-like material has an initial thickness of at least about 1.4 mm.
31. The substantially uniplanar integral geogrid according to claim 25, wherein the polyethylene terephthalate strands include substantially transversely oriented strands interconnected by substantially longitudinally oriented strands.
32. A starting material for making a substantially uniplanar integral geogrid, said starting material comprising:
a substantially uniplanar sheet-like material having holes or depressions therein that provides a plurality of interconnected, oriented strands and partially oriented junctions having an array of openings therebetween when the substantially uniplanar sheet-like material is uniaxially or biaxially stretched, with the substantially uniplanar sheet-like material being made of polyethylene terephthalate.
33. The starting material according to claim 32, wherein the stretched polyethylene terephthalate substantially uniplanar sheet-like material exhibits a substantially linear relationship between a stretch ratio and a specific tensile strength.
34. A method of making a substantially uniplanar integral geogrid, said method comprising:
stretching and orienting a substantially uniplanar sheet-like material having holes or depressions therein to provide a plurality of interconnected, oriented strands and partially oriented junctions, and to configure the holes or depressions as geogrid openings, with the substantially uniplanar sheet-like material and the substantially uniplanar integral geogrid being made of polyethylene terephthalate.
35. The method according to claim 34, wherein the polyethylene terephthalate substantially uniplanar sheet-like starting material is oriented by uniaxial or biaxial stretching.
36. The method according to claim 34, wherein the polyethylene terephthalate is crystalline polyethylene terephthalate.