Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1992-07-09
1994-06-14
Zitomer, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
428220, 435262, 523124, 523126, 523128, 524 9, 524 13, 524 27, 524 72, C08L 9700, C08L 9702
Patent
active
053210654
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a degradable plastic film including lignin as active vegetable filler.
BACKGROUND OF THE INVENTION
Photodegradable plastic films have also been known are known and more recently so-called biodegradable plastic films. The photodegradable plastic films are are obtained by introducing photoactive additives into a basic material which can be a polyolefin, for example. Generally, these additives are form by molecules containing oxygen and/or heavy metals the role of which is to initiate the formation of free radicals under the action of ultraviolet (UV) radiation; these radicals cause a rupture of the chains of the polymer and therefore make the polymer fragile, by making it weak and therefore mechanically degradable.
However, the use of certain additives which are strongly oxidizing causes the degradation to start immediately after the manufacture of the films, which has for consequence to reduce the storage capacity either of the master mixtures or of the films.
It should be noted that in agricultural uses of photodegradable films, portions of the films which are buried in the ground are protected from UV radiation and therefore not altered and not mechanically degradable, which has for its consequence to increase the scraps.
With respect to the biodegradable plastic films, they are obtained by the introduction of a so-called biodegradable organic filler such as starch which, consumed by the microorganisms, will make in turn the film fragile and therefore more easily degradable under the influence of the UV radiation.
The addition of starch as a consumable filler for microorganisms has consequences both concerning the fabrication of the film and in its mechanical properties; actually: starch is partially decomposed as soon as a temperature of 180.degree. C. is reached during the extrusion operation used in making the film; starch is not compatible with the polymers and therefore embrittles the films. Finally, the granulometry of the industrially available starch does not permit making films of small thickness. Yet, the thickness is an element of the cost price of the film, but also a parameter which governs the degradation speed of the film.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a new plastic film, for example based on ethylene copolymer (generally polyolefins) in which there has been introduced lignin which behaves as an organic biodegradable additive and which is consumed by the microorganisms, without reducing the other characteristics of the product, in particular its mechanical properties. Lignin which is in the form of a powder can result from the processes presently known and used for the manufacture of paper pulps, such as a process as follows known under the following definitions: lignin contaminated by chemical products such as sulphonates, soda, bisulphite . . ., and being in the form of pulverulent powder (with a grain diameter of about 1 to 5 microns), which permits making homogeneous films of a small thickness of about 20.+-.5 microns.
Lignin is a polymeric vegetable material made of methoxylated and hydroxylated cores forming a three-dimensional structure. It is a by-product obtained in the manufacture of paper pulp. The vegetable origin of lignin classifies it in the category of renewable products and, since it does not spoil the earth natural resources, lignin can be considered as an ecoproduct.
Due to the excellent compatibility of lignin with the ethylenic copolymers, the weight contents of lignin in the thermo-plastic polymer of the degradable plastic film, can be as high as 75% but will be preferably adjusted between 3 and 25%, which implies the use of master mixtures.
The combination of the photodegradable, biodegradable and oxidizing properties of lignin can be advantageously used here for obtaining a degradable film. Actually, lignin which is a vegetable material, biodegradable by mushrooms (micromycetes) and bacteria, contributes under certain conditions to the embrittlement of the plastic film.
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Bono Pierre
Lambert Claude
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