Composite material and process for production thereof

Details Composite material and process for production thereof Composite material and process for production thereof

1998-04-10

2003-06-17

Kelly, Cynthia H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S500000, C428S523000, C427S301000, C427S385500, C525S050000, C525S070000

Reexamination Certificate

active

06579596

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite material and to a method for producing it. Specifically, the present invention relates to a composite material produced by forming graft polymers nonuniformly on a substrate and also to a method for producing this composite material. More specifically, the present invention relates to a biodegradable composite material capable of exhibiting an excellent biodegradability together with other functions and also to a method for producing this biodegradable composite material.
2. Description of the Related Art
Because of the disposal problems of discarded goods such as synthetic plastics, a biodegradable resin, which is degraded by the action of microorganisms in soil, is drawing attention. Presently, known biodegradable resins include aliphatic polyesters and the like which are prepared by a chemical synthesis or a biosynthesis, resins utilizing naturally occurring polymers such as starch, cellulose, and the like, and chemically synthesized polymers such as polyvinyl alcohol, polyether, and the like. These materials are described in, e.g., Yoshiharu Doi, “Biodegradable Polymeric Materials” (Kogyo Chosakai Publishing Co., Ltd.).
Despite remarkable progress in biodegradable resin technologies, the use of biodegradable resins centers on wrappers and containers which are discarded after a single use, and the amount of use the biodegradable resins is also restricted by their high cost. Henceforth, biodegradable resins will expand their field of application as a highly functional material in addition to the wrappers and containers now in use. However, conventional biodegradable resins are mostly developed from the standpoint of degradability and, hence, the restrictions imposed on designing retard the development of biodegradable resins as functional materials.
Meanwhile, materials, which effectively utilize naturally occurring polymeric materials, are highlighted because of problems such as the depletion of petroleum resources and the release of CO
2
into atmosphere and, hence, one of the contemplated applications of naturally occurring resins is their use as a biodegradable resin. However, the attempt to impart functions to the naturally occurring polymeric materials is associated with problems. For example, one of the problems is that chemical modification impairs the excellent biodegradability inherent in the naturally occurring polymeric materials. Another problem is that it is difficult to obtain materials having a high level of functions comparable to those of synthetic polymers by a mere chemical modification of the substituent groups of the naturally occurring polymeric materials. As an embodiment of a naturally occurring polymeric material rendered more highly functional, a material which comprises a naturally occurring polymeric material having grafted thereto other polymeric material has been developed (J. Fibers and Textiles Soc. Japan, 102, Vol. 47, No.2, 1991). However, little is reported of the studies about the biodegradability of such a material.
A variety of graft polymerization methods are known as an effective means for modifying a material or a material surface. Examples of these methods include (1) a method wherein active sites are created either inside a material or on the surface of the material by utilizing the reaction between either radioactive rays, a redox initiator, or an ion-based initiator and the material or by utilizing the chain transfer of a radical initiator and thereafter a polymerizable unsaturated compound (hereinafter referred to as “a polymerizable monomer” on occasion) is polymerized by the active sites (described in, e.g., Adv. Polym. Sci., Vol. 4, p.111, 1965), (2) a method wherein polymerizable unsaturated bonds are introduced into a material and a polymerizable monomer is polymerized by the unsaturated bonds (described in, e.g., J. Polymer Sci., Part-A, 3, p.1031, 1965 and Japanese Patent Application Publication (JP-B) No. 5-5,845), and (3) a method wherein a structure which acts as an initiator is introduced into a material and a polymerizable monomer is polymerized by the structure (described in, e.g., Tappi, March, 56, p.97, 1973 and Japanese Patent Application Laid-Open (JP-A) No. 6-287,243).
Among these methods, method (1) is preferably employed, and a system utilizing an initiator in particular is widely employed.
As a graft polymerization initiator (hereinafter referred to simply as “an in initiator” on occasion), a redox initiator is industrially employed, and conventionally known examples of the redox-based initiator include ammonium cerium(IV) nitrate, Fenton's reagent (an H
2
O
2
/Fe system and the like), and a manganese-based system. According to graft polymerization using these initiators, the polymerization is generally performed in water or in a solvent system mixed with water. Details of these graft polymerization technologies illustrative of an example of a graft polymerization onto a hydrophilic polymer are described in, e.g., Fusayoshi Masuda, “Highly Water-absorbing Polymer, Polymeric New Materials, One Point-4”, Polymer Soc. Japan. Ed. and “J. Appl. Polymer Sci., 19, p.1257, 1975”.
According to conventional graft polymerization, the amount of the polymer grafted (generally referred to as a grafting ratio) onto a target material or the surface of a substrate to be grafted is controlled by the selection of an initiator, the type or structure of the initiation site, the concentration of the initiator, the concentration of a polymerizable monomer, and a solvent.
However, in a system according to a conventional method for graft polymerization, in particular a system using a redox initiator, it is difficult to control the molecular weight of the graft polymer and the grafting ratio, and it is also difficult to control the high-order structures, such as the morphology and the areal density, of the graft polymer which is formed on a substrate. That is, although it is possible to change the number of polymerizable monomers, which become the graft polymers, bonded to a unit area on the substrate surface by changing, for example, the concentration of the initiator, it has been impossible to make nonuniform the bonding density of the graft polymers on the surface of a substrate, for example, to obtain a surface structure comprising a region (domain) which has a plurality of graft polymers bonded and a non-grafted domain. Despite an attempt to obtain the above-described high-order structure by a method comprising partially masking the surface of a substrate and then performing a graft polymerization onto only the non-masked region (JP-B No. 62-7,931), this method is not practical because of limitations such as complexity of process and, in addition, this method cannot be applied to polyhedral substrates such as fibers and particles.
The high-order structural modification of the substrate surface as described above is useful as a means of modifying the surface physical properties, such as steric space, electrical potential, and free energy, in various applications, but conventional methods for this purpose are not satisfactory because the degree of freedom in controlling the high-order structure is low.
For the purpose of obtaining a so-called functional surface combining a plurality of functions on the substrate surface, a method hitherto employed consists of utilizing as a copolymer a graft polymer itself which is grafted onto a substrate. The problem of this method is that the modification of surface properties achieved by this method is only of microscopic order, and, therefore, the modification of surface properties by this method cannot provide the functions to match those which can only be achieved by some degree of macroscopic assembly of graft polymers.
A still further problem of the conventional method for graft polymerization has been that graft polymerization performed in an aqueous solvent produces a large amount of a polymer product not grafted onto the target material (this polymer is hereinafter referred to as “a

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