Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1997-08-08
1999-07-13
Lusignan, Michael
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
1562755, 1562757, 427 211, 427223, 427261, 427322, 4273831, 4273935, 427536, B32B 3100
Patent
active
059221615
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of modifying or tailoring the surface of polymers and/or polymer-based materials to control surface and interface chemistry and molecular structure.
BACKGROUND OF THE INVENTION
Polymeric or polymer based surfaces are often difficult to wet and bond because of low surface energy, incompatibility, chemical inertness, or the presence of contaminants and weak boundary layers. The lack of adequate adhesion at the substrate/adherent and/or reinforcement/matrix interfaces often results in poor material performance and limits the possible applications of the polymeric materials. Effective surface treatments are frequently required to overcome one or more of the abovementioned difficulties in order to achieve controlled or maximised composite performance and controlled level of adhesion with adhesives, coatings, etc.
In practical applications, solid polymeric material surfaces may also be required to exhibit a specific level or gradient of wettability by organic and/or inorganic liquids or vapours of these liquids. Depending on specific end-applications, the liquid phase or condensate may require to form a uniform film on the wettable solid's surface, or alternatively it may be required to bead-up on an unwettable liquid-repellent surface. With regard to the wetting capability by water-based media, the former material is defined as hydrophilic, and the later as hydrophobic. It is also possible that in some instances, an intermediate level of wettability is desirable.
Another important area of application of polymeric materials is in the biomedical field. To design a useful biomedical material, it is important to consider both bulk and surface properties of the material. Historically, selection of a biomedical material for a particular application has been based upon bulk property specifications. However, there is increasing recognition that a biomedical material must exhibit a specific surface chemical behaviour in order to minimise interfacial problems with host tissues and fluids. Thus, it is often required that the surface of biopolymer be chemically modified so that surface and interface behaviour could be controlled.
Various surface treatment processes have been developed to achieve different specific requirements. These include chemical oxidation with the use of oxidising agents; surface chemical grafting and various physical-chemical methods such as corona discharge; flame treatment; plasma treatment; and UV irradiation. Simple oxidative treatments by flame treatment, corona discharge, or chemical oxidation generally lead to a noticeable increase in surface hydrophilicity, and bonding ability as a result of the occurrence of oxygenated groups such as carboxyl, hydroxyl and carbonyl on the modified polymer surfaces. Such modified surface is, however, not stable and the chemistry and/or increased hydrophilicity is not permanent. This may be due to the partial removal low molecular weight oxidised material by a polar solvent or water from the oxidised surface. Alternatively, or in addition, it may be due to the reorientation of the surface functional groups which rotate inwardly into the bulk of the polymer during the storage or the use of such treated materials. Plasma treatment and/or plasma polymerisation is known to significantly improve bonding ability of the treated polymers or to achieve desired level of wettability as a result of selective incorporation of different types of chemical species onto the polymer surface through the use of an appropriate treatment gas or a monomer under controlled process conditions. Similarly to the oxidised surface, however, the plasma treated polymer surface is not stable in storage because of rotation and migration of the generated surface functional groups into the bulk of the material and the occurrence of post-chemical reactions within the modified surfaces. An additional drawback with plasma treatment or plasma polymerisation resides in the expensive process apparatus required and the high cost associated
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Li Sheng
Stanislaw Gutowski Wojciech
Wu Dong Yang
Commonwealth Scientific and Industrial Research Organisation
Lusignan Michael
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