CA1170390A

CA1170390A - Article for protecting metal substrates from corrosion

Info

Publication number: CA1170390A
Application number: CA000364263A
Authority: CA
Inventors: George Pieslak; Kathleen A. Erbes-Mrsny; Elena C. Fritchle
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1979-11-09
Filing date: 1980-11-07
Publication date: 1984-07-03
Also published as: GB2062654A; DE3071515D1; US4287034A; AU529726B2; AU6416080A; JPS5682866A; EP0028927B1; GB2062654B; EP0028927A1

Abstract

A B S T R A C T

Metal substrates such as pipes and pipelines are often protected from corrosion by providing the substrate with a protective cover that is bonded to the substrate by means of a sealant. In addition, a cathodic potential may be applied to the substrate to prevent loss of ions from the substrate due to electrochemical reactions. This can, however, lead to disbonding of the cover by a phenomenon known as "cathodic disbonding".
Cathodic disbonding may be reduced according to the in-vention by incorporation in the sealant at least 0.01%, preferably at least 0.1% by weight of an organic, non-phenolic polyhydroxy compound, for example a mono- or polysaccharide, a synthetic hydroxy-containing polymer or a polyhydric alcohol. The sealant may be provided as a pre-coated layer on a cover for the substrate, preferably on a dimensionally heat-recoverable cover.

Description

- 2 - MPO709 This invention relates to articles for protecting pipes from corrosion and to adhesive compositions used therein.

To protect pipes and pipelines formed from steel or other metals from corrosion, a protective coating is usually applied. The protective coating may be, for example, a polymeric sheet, tape or sleeve of, for example, a poly-ethylene, bonded to the surface of the pipe. Various adhesives and mastics may be used to bond the coating to the pipe. However, accidental perforations in the coating often occur during installation and use of the pipe or pipeline and expose areas of the pipe to the environment.

Corrosion of a steel or iron pipe when exposed to the environment is due to electrochemical reactions in which the pipe loses iron ions to water in the environment and a localized anodic region is created on the pipe. To prevent the development of these anodic regions and the attendant corrosion of the pipe, an electric current can be imposed along the length of the pipe. The pipe is connected to a negative electrical potential, thus causing the pipe to act as a cathode. In this way, further loss of iron ions is prevented. It is known that adhesive compositions used to bond a protective coating to a pipe are often adversely affected by this imposed electrical current. The result of this is a weakening of the adhesive bond between the coating and the steel pipe causing the coating to separate from the pipe exposing more of the surface of the pipe to the corros-ive conditions in the environment. This phenomenon is referred to in the art as "cathodic disbonding".

`` 1170390 According to one aspect of the present invention there is provided an article of a heat shrinkable material having coated on at least a part of the surface thereof an adhesive composition comprising an adhesive component and an aliphatic or alicyclic polyhydroxy eompound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms in an amount sufficient to impart improved resistance to cathodie disbondment to the adhesive composition, said adhesive component being a hot melt adhesive or a mastie.
Aeeording to another aspeet of the present invention there is provided a pipe having bonded to the surfaee thereof a polymeric eoating, said coating being bonded to said pipe with an adhesive composition comprising an adhesive eomponent and from about 0.01 to about 30 pereent by weight, based on the total weight of the adhesive eomposition, of an aliphatie or alicyclic polyhydroxy eompound in which hydroxyl groups are bonded to at least 50 pereent of the earbon atoms, said adhesive eomponent being a hot melt adhesive or a mastie.
Aeeording to a further aspeet of the present invention there is pro-vided a metal pipe whieh is eonneeted in an eleetrie eireuit sueh that said pipe forms a cathode; said pipe having bonded to the surfaee thereof a poly-merie eoating with an intermediate layer of an adhesive eomprising an adhesive component and from about 0.01 to about 30 percent by weight, based on the total weight of the eomposition of an aliphatic or alicyclic polyhydroxy eompound in whieh hydroxyl groups are bonded to at least 50 pereent of the earbon atoms, said adhesive eomponent being a hot melt adhesive or a mastie.
Aeeording to a further aspeet of the present invention there is pro-vided an adhesive eomposition eomprising an ethylene-ethyl aerylate or ethylene-vinyl aeetate eopolymer hot melt adhesive and from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive eomposition, of an aliphatie or alieyclie polyhydroxy eompound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms.

.', .
According to another aspect of the present invention there is provided a method of improving the resistance to cathodic disbondment of an adhesive which comprises incorporatinq into a hot melt adhesive or a mastic from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive composition, of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms.
. According to a further aspect of the present invention there is pro-vided a method of protecting a metal substrate from corrosion which comprises impressing an electrical current through said substrate such that said substrate . 10forms a cathode, and bonding to the surface of said substrate a protective coating by means of an adhesive composition comprising an adhesive component and from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive composition, of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least about 50 percent of the carbon atoms, said adhesive component being a hot melt adhesive or a mastic.
In the method and the arrangement according to the invention the adhesive composition or sealant may be applied to the substrate prior to appli-cation of the protective cover, although preferably the sealant and protective cover are provided as a single article as defined above.

- 3a -.
The polyhydroxy compound present in the sealant may be one that has one or more aromatic moieties in addition to aliphatic and or alicyclic moieties, but, if so, the hydroxy groups should be aliphatic and or alicyclic hydroxy groups, i.e. not bonded directly to the aromatic ring or rings.
Preferably the polyhydroxy compound is an aliphatic or ali-cyclic polyhydroxy compound, i.e. it contains no aromatic moieties. The polyhydroxy compound preferably has at least one hydroxy ground bonded to at Least half, especially at least 60%, and most especially at least 75% of its aliphatic or alicyclic carbon atoms.

Polyhydroxy compounds which can be used include, for example, monosaccharides, polysaccharides, hydroxy contain-ing synthetic polymers and polyhydric alcohols.

Polysaccharides that can be used include starches and cellulose and derivatives thereof, such as, amylose, amylo-pecti ~ cellulose acetate, cellulose nitrate, hydroxyethyl cellulose, ethyl hydroxyehtyl cellulose, hydroxypropyl cellulose, and the like. Monosaccharides which can be used include fructose, mannose, maltose, sucrose, glucose, ribose, raffinose, mannitol, sorbitol and similar sugars.
Derivatives such as lower alkyl derivatives of the mono-saccharides and mixtures of monosaccharides can be used.
Hydroxy containing polymers which can be used include polyvinyl alcohol, and various hydrolyzed polymers contain-ing aliphatic carbon atoms, preferably with hydroxyl groups on at least 50% of the carbon atoms. Aliphatic polyhydric alcohols include glycol, glycerol, pentaerythritol and the like.

" 1 170390 The sealant preferably contains at least 0.1% of the polyhydroxy com-pound by weight, but preferably not more than 30% and especially not more than 10~ of the polyhydroxy compound by weight, based on the total weight of the sealant. The preferred range for the content of the polyhydroxy compound is from 0.1 to 5% by weight. More than one polyhydroxy compound may be present in the sealant, and, if so, the numerical values for the content of polyhydroxy compound refer to the total content of all the polyhydroxy compounds.
The sealant is an adhesive, and can, in general, be any adhesive that is used to bond corrosion protection coatings to metal pipes or other substrates, particularly those used to bond a coating to a pipeline which will carry an impressed current to protect the pipeline from corrosion. Such adhesives include hot-melt adhesives for example those based on thermoplastic polyamides, polyolefins, polyesters, polyurethanes, polysulfides and the like. Mastics can also be used, for example low molecular weight polyisobutylene based mastic compositions. Particularly preferred adhesives are hot-melt adhesives contain-ing polyethylene and ethylene copolymers, for example, copolymers of ethylene with vinyl acetate, maleic anhydride, acrylic acid, methacrylic acid or an alkyl acrylate, for example ethyl acrylate. The most preferred adhesives are those based on ethylene-ethyl acrylate and ethylene-vinyl acetate.
Another embodiment provides a hot melt adhesive composition based on an ethylene-ethyl acrylate copolymer or an ethylene-vinyl acetate copolymer, which contains at least 0.01 percent by weight, based on the total weight of the adhesive, of a polysaccharide containing at least four monosaccharide units or a hydroxy-containing synthetic polymer, preferably polyvinyl alcohol.

i C - 5 -- ~ - MPO709 The sealant may also contain the usual additives such as tackifiers, fillers, waxes, rubber~ and stabilizers.
Tackifiers that are used include phenol-formaldehyde resins, hydrocarbon resins, vinyl toluene-alpha-methyl styrene copolymers, polyterpenes, phenol-terpene resins, dibasic acid modified esters, polymerized rosin esters, modified esters and rosins, aromatic hydrocarbon resins, and coumar and coumar-indene resins. Other tackifiers that can be included are well known. Fillers that can be used include pigments and reinforcing agents such as carbon blacks.
. , Waxes which are usually added to hot melt adhesives are crystalline waxes, such as, low molecular weight poly-ethylene, oxidized polyethylene waxes, ethylene-vinyl acetate copolymer wax, ethylene-acrylic acid copolymer wax, ethylene-acrylic acid copolymer wax ethylene-maleic an-hydride copolymer wax, atactic polypropylene, and the like.
~igh temperature properties may be improved by incorporation of high, low or medium density polyethylene, linear low density polyethylene or high temperature waxes. Rubbers which can be used include natural and synthetic rubbers, particularly ethylene-propylene rubbers, èthylene-propylene-diene rubbers, butyl rubbers, and thermoplastic elastomers such as those based on styrene-butadiene-styrene or styrene-isoprene-styrene linear or radial block co-polymers. Stabilizers which can be used include antiox-idants, such as phenolic antioxidants, hindered amine antioxidants, and the like.

The polyhydroxy compound can be blended with the other components to form a homogeneous sealant composition by conventional methods. Such methods include use of a two conventional methods. Such methods include use of a two roll mill, a Banbury mixer or a Brabender mixer. Temper-atures during the mixing or blending procedure should be from about 66C (150F) to about 149C (300F), preferably from about 121C (250F) to about 149C (300F). When possible, it is preferred to blend the components at a temperature above the melting point of the polyhydroxy compound to ensure uniform dispersion of the polyhydroxy compound in the adhesive composition.

Incorporation of an organic, n~n-phenolic polyhydroxy compound in the sealant has the advantage that certain properties of the sealant may be significantly improved.
For example, it has been found that the resistance to cathodic disbonding of various adhesives and mastics used with metals in corrosion protection applications can be improved.

The article according to the invention may for example, be in the form of a sheet, tape or sleeve coated on at least a portion of one surface thereof with an adhesives compos-ition, and is preferably dimensionally-recoverable.
Dimensionally recoverable articles are articles, the dimen-sional configuration of which may be made substantially to change when subjected to the appropriate treatment. Of particular interest are heat-recoverable articles, the dimensional configuration of which may be made substantially to change when subjected to heat treatment. ~eat-recoverable articles may be produced by deforming an orig-inal heat-stable configuration to a dimensionally heat-unstable configuration,~in which case the article will assume, or tend to assume, the orignal heat-stable con-figuration on the application of heat alone. Examples of i 1 7()3 30 heat-recoverable articles may be found in US Patent Specification No. 2,027,962 and UK Patent Specification ~o. 990,235.

When in the form of a sheet or tape, the article is usually coated on over one entire surfa oe. The sheet or tape is pla oe d on the substrate to be protected with the adhesive coated surfa oe placed in contact with the substrate and then heated to bond the article to the substrat The substrate can be any metal sub-strate sought to be protected fram corrosion but in practi oe the substrate is usually a metal pipe and in particular an iron or steel pipe. The sheet or tape is wrapped around the pipe and heated to heat shrink the sheet or tape into the pipe and bond it to the pipe with the adhesive.

When the heat shrinkable article is in the form of a sleeve it is coated with adhesive on the interior surface thereof. T~le sleeve can be a tube of continuous circumeren oe or a tube which is longitudinally split. The tube is positioned around the pipe and heated to shrink the sleeve onto the pipe and melt and adhesive to bond the sleeve to the pipe.

If a longitudinally split sleeve is used, the longitudinal edges must be held to-gether in some manner, usually with a channel, during the heat shrinking step.

The protective cover is preferably formed fram a polyolefin for example poly-ethylene or polypropylene. Other polymers such as polyvinyl chloride and poly-meric blends thereof can also be used. Particularly preferred is cross-linked polyethylene.

1 1703~0 The articles and adhesive compositions ~f this invention can be used for other purposes besides protection of metal substrates. The presence of the polyhydroxy compound in the sealant can, in some cases, improve the adhesion properties with various substrates, including other metals, as well as steel and iron, and polymeric substrates such as articles of polyethylene, polypropylene, polyvinyl chloride and the like. In the pipe protection context it has been found that a patch of polymeric sheet material coated with the adhesive composition can be used to repair.damage to the protective coating on the pipe.

The following examples illustrate the invention. In these examples adhesive compositions were prepared containing an adhesive component and a polyhydroxy compound. The ad-hesives were tested for resistance to cathodic disbondment by using the adhesive to bond a heat shrinkable sleeve of polyethylene to a steel pipe. The polyethylene coated pipe was then tested by the method of ASTM G-42-75 to determlne the resistance of the adhesive to cathodic disbonding.

Adhesive compositions were prepared by thoroughly mixing the ingredients in a two-mill roll at a mixing temperature of 121 to 14gC (250 to 3Q0F~.

An adhesive component was prepared by blending 45 parts of an ethylene-ethyl acrylate copolymer containing 18% ethyl acrylate, 31.5 pa_ts of an ethylene-acrylic acid copolymer 1 1703~

wax having an acid number of 40, 5 parts of a phenol-formaldehyde resin tackifier, 8 parts of an ethylene-propylene-1,4-hexadiene terpolymer ~ubber, 10 parts of carbon black and 0.5 parts of 1,2-dihydro-2,2,4-trimethyl quinoline. To the adhesive component was added a poly-hydroxy compound as designated below for each example:

EXAMPLE AMOUNT ~OL U~D~O~Y COM~OUND

l ~Control) - None 2 10 parts Polyvinyl alcohol

3 10 parts Anhydrous glucose

4 10 parts Pentaerythritol 2 parts Mannitol 6 5 parts Sorbitol The adhesive compositions were tested for their resistance to cathodic disbonding by the following test procedure. The results are shown in the Table.

The cathodic disbonding resistance of an adhesive can be tested by the test method fGund in ASTM G-42-75, method A.

The adhesive composition to be tested was pressed into slabs, 152~4mm x 152.4mm x 0.635mm (6 inches x 6 inches x O . 023 inch), in a hot press between two "Teflon ~ poly-tetrafluoroethylene, coated plates.
~ tr~dema~

~ MPO709 The surface of a steel pipe, 305mm (12 ~nches) long and 51mm (2 inches) in diameter was grit blasted and degreased with solvent and preheated to 121 to 177C (250 - 350F) with a torch. The sample adhesive slab, trimmed to 152.4mm x 101.6mm x 0.635mm (6 inches x 4 inches x 0.025 inch), was placed on the preheated pipe and a heat shrinkable sleeve of cross-linked polyethylene was placed over it and heated to shrink the sleeve over the adhesive and pipe. One end of the pipe was then sealed with a heat shrinkable cap.
, A hole (holiday) was drilled through the polyethylene coating and adhesive in the middle of the length ~~ pipe to expose the metal surface of the pipe at that point. The pipe was then immersed in an electrolyte solution comprising water and one weight per cent of each of sodium chloride, sodium sulphate, and sodium carbonate. A potential of -1.5 volts was applied to the pipe thus making the pipe a cathode in the electrolyte solution which also contains a sacri-ficial anode. The sample and electrolyte solution were maintained at a tempeature of 80C for five days. The pipe was then removed and the area around the holiday inspected to determine the extent of disbonding, i.e., the area over which the adhesive bond between the polyethylene coating and the pipe was weakened permitting the polyethylene coating and adhesive to be peeled away. The approximate radius of the disbonded area was measured in millimetres (mm) and re-corded.

l 170390 An adhesive composition containing the followins ingredients was prepared and tested as in Examples 1 - 6. This adhesive composition contained 45 parts of an ethylene-ethyl acrylate copolymer containing 18% ethyl acrylate, 32 parts of poly-ethylene microcrystalline wax, 5 parts of phenol-formalde-hyde resin tackifier, 8 parts of ethylene-propylene-1, 4-hexadiene terpolymer rubber, 8 parts of carbon black and 1 part of 1,2-dihydro-2,2, 4-trimethyl quinoline and 5 parts of anhydrous glucose. The results are given in the Table.

An adhesive containing the following ingredients was pre-pared and tested as in Examples 1 - 6. This adhesive contained 35 parts of an ethylene-ethyl acrylate copolymer containing 18% ethyl acrylated, 25 parts of a low molecular weight thermoplastic polyamide resin, 25 parts of an ethylene-maleic anhydride copolymer wax having an acid number of 16, 10 parts of an ethylene-propylene-1, 4-hexadiene terpolymer rubber, 2 parts of carbon black and 2 parts of 1,2-dihydro-2,2,4-trimethyl quinoline.

To the adhesive prepared in Example 8, 10 parts of polyvinyl alcohol was added and incorporated into the adhesive. The adhesives of Examples 8 and 9 were tested as above. The resul's are shown in the Table.

TABLE

EXAMPLE POLYHYDROXY AMOUNT OF POLYHYDROXY CATHODIC
COMPOUNDCOMPOUND (PARTS) DISBONDING
RADIUS

1 None - Complete Disbonding 2 Polyvinyl alcohol 10 9mm 3 Glucose 10 7mm 4 Pentaerythritol 10 7mm Mannitol 2 1Omm 6 Sorbitol 5 5mm 7* Glucose 5 8mm 8 None - Complete - Disbonding 9 Polyvinyl alcohol 10 16mm *This adhesive was also tested as above but at 95C. The cathodic disbonding radius was 15mm.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An article of a heat shrinkable material having coated on at least a part of the surface thereof an adhesive composition comprising an adhesive component and an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms in an amount sufficient to impart improved resistance to cathodic disbondment to the adhesive composition, said adhesive component being a hot melt adhesive or a mastic.

2. An article in accordance with claim 1 wherein said article is a sheet.

3. An article in accordance with claim 1 wherein said article is a tape.

4. An article in accordance with claim 1 wherein said article is a sleeve.

5. An article in accordance with claim 1 wherein said heat shrinkable material is a polymeric material.

6. An article in accordance with claim 5 wherein said polymeric material is polyethylene.

7. An article in accordance with claim 5 wherein said polymeric material is cross-linked polyethylene.

8. An article in accordance with claim 1 wherein said adhesive component is a hot melt adhesive.

9. An article in accordance with claim 8 wherein said hot melt adhesive comprises an ethylene-ethyl acrylate copolymer hot melt adhesive.

10. An article in accordance with claim 8 wherein said hot melt adhesive comprises an ethylene-vinyl acetate copolymer hot melt adhesive.

11. An article in accordance with claim 1 wherein said polyhydroxy com-pound is glucose.

12. An article in accordance with claim 1 wherein said polyhydroxy com-pound is sorbitol.

13. An article in accordance with claim 1 wherein said polyhydroxy com-pound is mannitol.

14. An article in accordance with claim 1 wherein said polyhydroxy com-pound is polyvinyl alcohol.

15. An article in accordance with claim 1 wherein said polyhydroxy com-pound is pentaerythritol.

16. A pipe having bonded to the surface thereof a polymeric coating, said coating being bonded to said pipe with an adhesive composition comprising an adhesive component and from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive composition, of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms, said adhesive component being a hot melt adhesive or a mastic.

17. A pipe in accordance with claim 16 wherein said pipe is of steel.

18. A pipe in accordance with claim 16 wherein said polymeric coating is polyethylene.

19. A pipe in accordance with claim 18 wherein said polymeric coating is cross-linked polyethylene.

20. A pipe in accordance with claim 16 wherein said adhesive component is a hot melt adhesive.

21. A pipe in accordance with claim 20 wherein said hot melt adhesive is an ethylene-ethyl acrylate copolymer hot melt adhesive.

22. A pipe in accordance with claim 20 wherein said hot melt adhesive comprises an ethylene-vinyl acetate copolymer hot melt adhesive.

23. A pipe in accordance with claim 16 wherein said polyhydroxy compound is glucose.

24. A pipe in accordance with claim 16 wherein said polyhydroxy compound is sorbitol.

25. A pipe in accordance with claim 16 wherein said polyhydroxy compound is mannitol.

26. A pipe in accordance with claim 16 wherein said polyhydroxy compound is polyvinyl alcohol.

27. A pipe in accordance with claim 16 wherein said polyhydroxy compound is pentaerythritol.

28. A metal pipe which is connected in an electric circuit such that said pipe forms a cathode; said pipe having bonded to the surface thereof a poly-meric coating with an intermediate layer of an adhesive comprising an adhesive component and from about 0.01 to about 30 percent by weight, based on the total weight of the composition of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms, said adhesive component being a hot melt adhesive or a mastic.

29. A pipe in accordance with claim 28 wherein said pipe is of steel.

30. A pipe in accordance with claim 28 wherein said polymeric coating is polyethylene.

31. A pipe in accordance with claim 30 wherein said polymeric coating is cross-linked polyethylene.

32. A pipe in accordance with claim 28 wherein said adhesive component is a hot melt adhesive.

33. A pipe in accordance with claim 32 wherein said hot melt adhesive is an ethylene-ethyl acrylate copolymer hot melt adhesive.

34. A pipe in accordance with claim 32 wherein said hot melt adhesive comprises an ethylene-vinyl acetate copolymer hot melt adhesive.

35. A pipe in accordance with claim 28 wherein said polyhydroxy compound is glucose.

36. A pipe in accordance with claim 28 wherein said polyhydroxy compound is sorbitol.

37. A pipe in accordance with claim 28 wherein said polyhydroxy compound is mannitol.

38. A pipe in accordance with claim 28 wherein said polyhydroxy compound is polyvinyl alcohol.

39. A pipe in accordance with claim 28 wherein said polyhydroxy compound is pentaerythritol.

40. An adhesive composition comprising an ethylene-ethyl acrylate copoly-mer hot melt adhesive and from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive composition, of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms.

41. An adhesive composition in accordance with claim 40 wherein said polyhydroxy compound is glucose.

42. An adhesive composition in accordance with claim 40 wherein said polyhydroxy compound is sorbitol.

43. An adhesive composition in accordance with claim 40 wherein said polyhydroxy compound is mannitol.

44. An adhesive composition in accordance with claim 40 wherein said polyhydroxy compound is polyvinyl alcohol.

45. An adhesive composition in accordance with claim 40 wherein said polyhydroxy compound is pentaerythritol.

46. An adhesive composition comprising an ethylene-vinyl acetate copolymer hot melt adhesive and from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive composition, of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms.

47. An adhesive composition in accordance with claim 46 wherein said polyhydroxy compound is glucose.

48. An adhesive composition in accordance with claim 46 wherein said polyhydroxy compound is sorbitol.

49. An adhesive composition in accordance with claim 46 wherein said polyhydroxy compound is mannitol.

50. An adhesive composition in accordance with claim 46 wherein said poly-hydroxy compound is polyvinyl alcohol.

51. An adhesive composition in accordance with claim 46 wherein said poly-hydroxy compound is pentaerythritol.

52. A method of improving the resistance to cathodic disbondment of an adhesive which comprises incorporating into a hot melt adhesive or a mastic from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive composition, of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms.

53. A method in accordance with claim 52 wherein said adhesive is a hot melt adhesive.

54. A method in accordance with claim 53 wherein said hot melt adhesive is an ethylene-ethyl acrylate copolymer hot melt adhesive.

55. A method in accordance with claim 53 wherein said hot melt adhesive is an ethylene-vinyl acetate copolymer hot melt adhesive.

56. A method in accordance with claim 52 wherein said polyhydroxy compound is glucose.

57. A method in accordance with claim 52 wherein said polyhydroxy compound is sorbitol.

58. A method in accordance with claim 52 wherein said polyhydroxy compound is mannitol.

59. A method in accordance with claim 52 wherein said polyhydroxy compound is polyvinyl alcohol.

60. A method in accordance with claim 52 wherein said polyhydroxy compound is pentaerythritol.

61. A method of protecting a metal substrate from corrosion which com-prises impressing an electrical current through said substrate such that said substrate forms a cathode, and bonding to the surface of said substrate a protective coating by means of an adhesive composition comprising an adhesive component and from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive composition, of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least about 50 percent of the carbon atoms, said adhesive component being a hot melt adhesive or a mastic.

62. A method in accordance with claim 61 wherein said protective coating is a polymeric material.

63. A method in accordance with claim 62 wherein said polymeric material is polyethylene.

64. A method in accordance with claim 62 wherein said polymeric material is cross-linked polyethylene.

65. A method in accordance with claim 61 wherein said adhesive is a hot melt adhesive.

66. A method in accordance with claim 61 wherein said hot melt adhesive is an ethylene-ethyl acrylate copolymer hot melt adhesive.

67. A method in accordance with claim 61 wherein said hot melt adhesive is an ethylene-vinyl acetate copolymer hot melt adhesive.

68. A method in accordance with claim 61 wherein said polyhydroxy com-pound is glucose.

69. A method in accordance with claim 61 wherein said polyhydroxy com-pound is sorbitol.

70. A method in accordance with claim 61 wherein said polyhydroxy com-pound is mannitol.

71. A method in accordance with claim 61 wherein said polyhydroxy com-pound is polyvinyl alcohol.

72. A method in accordance with claim 61 wherein said polyhydroxy compound is pentaerythritol.

73. An adhesive composition comprising an ethylene-ethyl acrylate or ethylene-vinyl acetate copolymer hot melt adhesive and from about 0.01 to about 30 percent by weight, based on the total weight of the adhesive composition, of an aliphatic or alicyclic polyhydroxy compound in which hydroxyl groups are bonded to at least 50 percent of the carbon atoms.