Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Patent
1980-03-06
1983-05-10
Ball, Michael W.
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
20415921, 264 22, 264109, C08G 202
Patent
active
043828477
DESCRIPTION:
BRIEF SUMMARY
It is well known that so-called ionising radiation, both mechanically produced radiation and that obtained from natural sources, can cause chemical and physical changes in polymeric material. Thus, some polymeric materials obtain an increase in their molecular weight and in their melting point subsequent to being exposed to such radiation, owing to the fact that new chemical bonds are formed in the material. Other polymers are influenced to a lesser extent or are decomposed into products of lower molecular weight, the mechanical properties of these polymers often being impaired at the same time.
The effect caused by the radiation can be influenced in some way, by exposing the polymer to said radiation in the presence of various additives, for example in a manner such that a material which has been decomposed can also be re-linked and the properties thereof improved thereby. Further, it has been found that the presence of air when irradiating the material also has a certain significance, since in many cases the oxygen accelerates the decomposition of the material.
It is also known that cellulose, cellulose derivatives and various natural cellulose composites, such as wood and vegetable fibres, belong to those polymeric materials most sensitive to radiation. If one excepts an insignificant positive effect at very small doses, i.e. .ltoreq.10 krad, the mechanical properties of these materials are greatly impaired with increasing doses of radiation. It is also known that the properties of a plurality of condensation polymers between formaldehyde and urea, melamine or different phenol types, are impaired by radiation.
The present invention is based on the surprising discovery that chipboard or particle board bonded with formaldehyde-urea-resin exhibits highly improved mechanical properties subsequent to exposing the board to radiation.
The invention relates to a method of manufacturing bonded products which may be comprised fully or partially of cellulose or cellulose derivative, e.g. saw dust, wood chips, paper or vegetable fibres, the adhesive used being a condensation resin between an aldehyde, e.g. formaldehyde, and urea, melamine or a phenol type, and its widest aspect is mainly characterised by the fact that the product is irradiated to at most 5 Mrad with ionising radiation, the material undergoing a certain degree of cross-linking and residual quantities of uncured adhesive substances being reduced simultaneously therewith. One Mrad corresponds to an amount of energy taken up in the material of 10 Joule/g or 10 Ws/g.
In order to improve the properties of the aforementioned products, it is also desirable to be able to increase the content of aldehyde in the adhesive. This cannot be done, however, without the surplus being removed in some way. The present invention constitutes a significant step forward in this respect, owing to the fact that, in addition to improving the mechanical properties of the products, the radiation also contributes to reducing the residual content of aldehyde in the material.
The invention can also be applied together with various additives containing those functional groups which experience has shown will improve the extent to which cross-linking takes place when the material is subjected to radiation. An example of such an additive is hydrocarbon with olefinic, acrylic or other comparable groups. It also lies within the scope of the invention to modify the adhesive substance itself, in a manner such that these groups are chemically bound to one or more of the components of the resin.
EXAMPLE 1
Five groups of four test plates of chipboard or particle board bonded with urea-formaldehyde-resin were irradiated with .sup.60 Co.gamma.-radiation in different dosages, and the surface hardness of the plates was determined at different locations by forcing a ball into the surface of the plates.
______________________________________ Dose (Mrad) Surface hardness (working units)
Blind-test 2.17 .+-. 0.13
0.10 2.41 .+-. 0.03
0.33 2.35 .+-. 0.06
1.0 2.31 .+-. 0.09
4.0 2.2
REFERENCES:
patent: 2668133 (1954-02-01), Brophy et al.
patent: 3140197 (1961-07-01), Heberlein et al.
patent: 3549509 (1970-12-01), Cosalina
Moslemi, "Particle Board", vol. 1, p. 91, 1974, Southern Illinois University Press.
Akesson Arne
Reitberger Torbjorn
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