WO1982002396A1

WO1982002396A1 - Improvement of properties of plastic containing mixture

Info

Publication number: WO1982002396A1
Application number: PCT/SE1981/000397
Authority: WO
Inventors: Ab Celloplast; Josef Kubat
Original assignee: Ab Celloplast
Priority date: 1981-01-05
Filing date: 1981-12-30
Publication date: 1982-07-22
Also published as: SE430342B; SE8300583D0; SE8300583L

Abstract

Plastic containing mixtures containing 0.1 - 30% by weight, calculated on the total weight of the mixture, of a substance improving the internal adhesion between the phase boundaries of the heterogeneous system, which substance is selected among aromatic mono-, di-, tri-, and tetracarboxylic acids, and their anhydrides and esters, which are solids with a melting point in excess of 30`C. By adding such substances, the property profile of the plastic containing mixtures is improved, which mixtures apart from one or more plastics also can contain one or more fillers or reinforcing agents.

Description

Improvement of properties of plastic containing mixtures

Normally, common polymers are not compatible. This may result in a number of unwanted effects with regard to the property profile when plastic containing mixtures are processed, as for instance when recycling the plastics fraction of domestic waste. The insufficient adhesion between the different phases of such a mixture results not only in anomalously low stiffness (modulus of elasticity) and tensile stress values, but also in unacceptably low breaking elongation values which, in turn, are related to a pronounced brittleness of products made of mixed plastics.

Apart from the already mentioned plastics fraction in household waste, consisting mainly of polyolefins/ polystyrene and polyvinylchloride, processing of mixed plastics occurs also in a number of other cases as, for instance, in recycling of plastics in connection with recovery of metals from cable waste, etc. In many cases, such plastics mixtures may also contain fillers, impurities such as cellulose fibres, textiles, and other constituents originating from the waste material itself, or added separately afterwards. In such cases, the insufficient adhesion between the different phases of such a system results in a further deterioration of the property profile. Needless to say, problems of this type also occur when using plastics mixtures based on virgin materials (plastic alloys, etc.).

It is known that the effect of an insufficient adhesion (wetting) can be eliminated only partly by a more intense mechanical treatment during the processing step before the final product is formed. In order to eliminate these disadvantages one has, instead, tried to use certain substances as additives, which substances have the ability to increase the adhesion between the various phases constituting the mixture. Such an adhesion may be brought about by chemical bonds and by a change in the surface energy distribution within the system.

Among the additives of the later type, one may mention chlorinated polyethylene, ethylene-vinylacetate polymer and various elastomers (see Reuse of Plastics from Solid Wastes, Ram, A. et al., Pol. Eng. Sci. 17, 1977, p. 274, and Chlorinated Polyethylene Modification of Blends Derived from Waste Plastics, Part 1: Mechanical Behaviour, Paul, D.R. et al., Pol. Eng, Sci. 13, 1973, p. 202). One of the disadvantages when using such compatibilizing additives are the relatively large quantities needed to attain technically interesting effects. Neither is the price of said substances sufficiently low in order to make their use common. Among other additives which have been suggested one may mention polyethyleneimine, neutralized acidic phosphoric esters of long-chain fatty alcohols, or coupling agents like titanates and silanes, as described in the Swedish patent 7901935-2 in connection with improving the properties of mixed systems containing a certain fraction of cellulose fibres,

The aim of the present invention is to eliminate certain disadvantages, associated with the low internal adhesion between different plastic materials, and between fillers or reinforcing agents for plastics, primarily of cellulose fibre type, through the use additives previously not used for this purpose. These additives are aromatic mono-, di-, tri- and tetracarboxylic acids and their anhydrides and esters, these substances being solids with a melting point in excess of 30ºC. Among additives suitable for the present purpose one thus may mention various isomers of phthalic acid, pyromellitic acid, trimellitic acid, alkyl- and arylterephthalates, such as dimethylterephthalate, and rosin acids, such as abietic acid.

A suitable amount of these substances to be added is from about 0.1 to about 30% by weight, an even more suitable amount being 0.5 to 15% by weight, preferably 1-10% by weight based on the whole mixture.

The effects which can be achieved by such additives are illustrated by the following examples, where the added amount relates to per cent by weight of the whole mixture,

A mixture of low density polyethylene (LDPE), plasticized PVC (50 pph DOP) and normal polystyrene was homogenized on a Buss-KoKneter PR 46 machine at 190°C together with 10% of dimethylterephthalate (DMTP). The homogenized mixture was injection moulded to test bars according to DIN 53455. When determining the mechanical parameters with a tensile testing machine (Instron 1192, strain rate 20 mm/min), the tensile strength (α _B) of the test bars was increased by 10% and the breaking elongation (ε_B) by 75% when compared with similarly prepared test bars not containing DMTP. The addition of 5% abietic acid to the same mixture resulted in an increase of α _B by 25% and that of ε_B by 50%,

When adding DMTP or abietic acid to binary mixtures of said plastics, homogenized and injection moulded as mentioned above, improvements in properties were obtained which to a higher degree than in the above example with the ternary mixture reflected the selectivity of the various additives. When adding 15% DMTP to the system PE-PS (50:50), a doubling of the modulus and a threefold increase of the tensile strength er thus were noted, while the breaking elongation fell from 8% to 3%. When using 10% abietic acid in the same system, the modulus increase was about 110%, while α_B was three times higher. The elongation of break fell from 100% to about 30%, the latter value being more than sufficient in technical applications.

In the system PS-plasticized PVC, a decrease of the modulus and α_B was noted when adding DMTP or abietic acid, while ε_B showed a dramatic increase. Thus, when adding 10% DMTP to such a mixture, an ε_B-value of about 30% was measured and with 5% abietic acid 100%, to be compared with the ε_B-value of the untreated mixture which was ε _B = 2%.

These examples illustrate the selectivity for various systems of the additives discussed in the present invention, in the first hand with the regard to the well-known balance between the modulus and α_B on one side, and ε_B on the other.

Also when modifying the property profile of plastics and plastic containing mixtures including cellulose fibres or wood flour remarkable effects were noted. As an example we mention a doubling of the modulus of an LDPE-35% wood flour mixture when adding 10% DMTP (the modulus increased from 600 to 1200 MPa). At the same time, α_B increased from 9 to 14 MPa. Phthalic acid added in an amount of 10% had a slightly smaller effect; the modulus thus increased from 600 to 900 MPa, while the tensile strength remained practically unchanged. Also in these cases, a decrease in ε _B , normally associated with higher modulus values, was observed. When using cellulose fibres (bleached or unbleached sulphate pulp) similar results were recorded. The homogenization of the mixtures used was performed in a Buss-KoKneter, as mentioned in the experiments described above; it was followed by injection moulding the tensile test bars.

Claims

1.A plastic containing mixture comprising in a heterogeneous system a mixture of one or more thermoplastic resins and optionally one or more fillers or reinforcing agents characterized in that it contains an addition of from 0.1 to 30 percent by weight, based on the total mixture, of an agent which improves the internal adhesion between the phase boundaries of the heterogeneous system, said agent being selected from aromatic mono-, di, tri-or tetracarboxylic acids and anhydrides and esters thereof which are solids having a melting point in excess of 30ºC.

2. A plastic containing mixture according to claim 1 characterized in that the plastic consists of the plastic fraction of domestic waste which essentially consists of polyolefins, PVC and polystyrene and a certain_ amount of cellulose fibre material as a filler.

3. A plastic containing mixture according to claim 1 or 2 characterized in that the adhesion promoting agent is dimethylterephthalate.

4. A plastic containing mixture according to claim 1 or 2 characterized in that the adhesion promoting agent is abietic acid.

5. A plastic containing mixture according to claim 1 or 2 characterized in that the adhesion promoting agent is phtalic acid.

6. A plastic containing mixture according to any of the preceeding claims characterized in that it contains ligno-cellulose material in an amount of from 1 to 90 percent by weight of the mixture.

7. An agent which promotes the internal adhesion of heterogeneous systems of plastic containing mixtures which comprise a mixture of one or more plastics and optionally one or more fillers or reinforcing agents characterized in that it is selected from aromatic mono-, di-, tri- or tetra-carboxylic acids and anhydrides or esters thereof which are solids having a melting point above 30ºC.

8. An adhesion promoting agent according to claim 7 characterized in that it is dimethyl terephthalate.

9. An adhesion promoting agent according to claim 7 characterized in that it is abietic acid.