GB2152938A

GB2152938A - Solvent treating polymers

Info

Publication number: GB2152938A
Application number: GB08501299A
Authority: GB
Inventors: Drahomir Vesely
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-01-18
Filing date: 1985-01-18
Publication date: 1985-08-14
Also published as: GB8501299D0; GB8401297D0

Abstract

An improved process for the production of a non-cellular thermoplastic polymeric material comprises: (i) contacting the non-cellular thermoplastic polymeric material with a swelling agent therefor; (ii) removing at least a portion of the swelling agent to provide a non-cellular thermoplastic polymeric material of reduced density and/or different micromorphology; and thereafter (iii) extruding the non-cellular thermoplastic polymeric material of reduced density and/or different micromorphology. In the Example PVC is treated with tetrahydrofuran and extruded as pipe stock.

Description

SPECIFICATION Solvent treating polymers This invention relates to improved processes for the production of non-cellular, extruded, thermoplastic polymers; and to thermoplastic polymers so produced. More particularly, this invention relates to improved processes for the production of noncellular, extruded, thermoplastic polymers, for example halo-substituted vinyl polymers such as poly(vinyl chloride) (PVC), utilising polymers of reduced density and/or different micro morphology, especially for extrusion in the form of pipe stock.

This invention is described with particular, but not exclusive, reference to PVC.

At the present time, a considerable tonnage of PVC is used for the manufacture of pipe stock. The grade of PVC principally used for such manufacture is a rigid vinyl of high molecular weight; and its processing is effected without the use of plasticiser. The resulting products, by reason of their chemical inertness, enjoy widespread use especially where the transported fluid would otherwise corrode (for example, saline aqueous media) or adhere to (for example, sour crude oil values) the interior of the pipe. However, the processing of such grades of PVC to form pipe stock involves substantial energy investment by reason of the high processing temperatures and pressures employed; moreover, the forming process results in same heterogeneity of product and degradation of the PVC leading to embrittlement.

This invention seeks to overcome, or at least ameliorate, the aforementioned disadvantages.

According, therefore, to one aspect of this invention there is provided an improved process for the production of a non-cellular, extruded, thermoplastic polymeric material, which process comprises: (i) contacting the non-cellular thermoplastic polymeric material with a swelling agent therefor; (ii) removing at least a portion of the swelling agent to provide a non-cellular thermoplastic polymeric material of reduced density and/or different micromorphology; and thereafter (iii) extruding the non-cellular thermoplastic polymeric material of reduced density and/or different micromorphology.

Indications that the micromorphology of the thermoplastic polymeric material is different are provided by our findings, in relation to PVC, that Tg is reduced even when the swelling agent is removed to the extent that it cannot be detected. In general, however, the swelling agent need be removed only to the extent that the amount remaining does not exceed the solubility of the swelling agent in the thermoplastic polymeric material at the extrusion temperature. Preferably, the extrusion is effected at a temperature below the boiling point, at the extrusion pressure, of the swelling agent.

By "non-cellular" is meant herein that the thermoplastic polymeric material is not foamed to an open or closed cellular structure by the presence of a pneumatogen.

It has been found that, by reducing the density and/or altering the micromorphology of the thermoplastic polymeric material in accordance with this invention, a lower extrusion temperature may be utilised in step (iii) to achieve a given degree of processing. This reduces the amount of degradation to which the material is subjected and increases the toughness of the resulting product.

The improved process of this invention is applicable to any thermoplastic polymeric material for which at least one swelling agent exists which, on its at least partial removal from the swollen thermoplastic polymeric material, results in a reduction in density and/or alteration of the micromorphology of that thermo-plastic polymeric material. Examples include polyolefins such as polyethylene, polypropylene and ethylene/propylene copolymers; polyacetals such as polyoxymethylene; and halogenated polyolefins: for example, polytetrafluoroethylene, halo-substituted vinylidene polymers such as poly(vinylidene dichloride) and poly(vinylidene difluoride), and halo-substituted vinyl polymers such as PVC, the process being of particular benefit to PVC stock.

The process of this invention is applicable to both thermo plastic homo-and co-polymeric materials; and to blends thereof.

Sweiling agents useful in the process of this invention desirably have both a solubility parameter, 8, which differs from that of the thermoplastic polymeric material by less than 5 cal i ml- and an interaction parameter, X, which is less than 1. In the case of PVC5 varies from 9.4 to 10.8.Useful swelling agents include anisole, benzyl alcohol, bromobenzene, I-bromonaphthalene, butyl acetate, y-butyrolactone, chlorobenzene, cyclohexanone, cyclohexene oxide, cyclopentanone, diamyl sebacate, 1,2-dibromoethane, di(2-butoxyethanol)phthalate, dibutyl phthalate, 0dichlorobenzene, 1,2-dichloroethane, diethyl phthalate, diethyl sebacate, dihexyl adipate, dihexyl phthalate, dihexyl sebacate, diisopropyl ketone, dimethylformamide, dimethyl sebacate, dimethyl sulfoxide, di-n-octyl succinate, di(2-ethylhexyl)phthalate, dioxane, ethyl acetoacetate, ethylene oxide, isophorone, mesityl oxide, methyl amyl ketone, methyl ethyl ketone, methyl isopropyl ketone, methyl n-propyl ketone, morpholine, nitrobenzene, 1-nitropropane, p-propiolactone, tetrahydrofuran, tetrahydrofurfuryl alcohol, tetrahydropyran, tributyl phosphate, tricresyl phosphate, triethyl phosphate, trimethylene oxide and xylene.

Mixtures of liquids can also show swelling agent properties: examples include acetone-carbon disulphide, acetone-perchloroethylene, mixtures of N,Ndisubstituted amides with cyclic ethers, aliphatic ketones, alkyl-substituted pyridines and aromatic hydrocarbons. Preferred swelling agents are cyclohexanone and tetrahydrofuran, especially tetrahydrofuran.

In the case of HDPE, trichloracetylene; aromatic hydrocarbons such as toluene and xylene; and cycloaliphatic hydrocarbons such as decalin may be used, with decalin being preferred.

In accordance with this invention, the swelling agent may be contacted in step (i) with the thermoplastic polymeric material over a wide range of temperatures, suitably O"C to 50"C, and pressures at which the swelling agent remains liquid. For example, tetrahydrofuran is found rapidly to swell PVC at ambient temperature and pressure. It is preferred that at least a portion of the swelling agent is removed in step (ii) by subjecting the swollen thermoplastic polymeric material to elevated temperature or reduced pressure and, preferably, both. Not all the swelling agent need be removed in step (ii): some may be removed at a later stage, for example during the forming step (iii).Swelling agent may also be removed during a pre-processing step; for example, by rolling it at a temperature above the glass transition temperature such as above 80"C for example 85" to 90"C.

The thermoplastic polymeric material should be contacted with the swelling agent so as to provide as low a density and/or as great a change in micromorphology as possible at the end of step (ii). For example, tetrahydrofuran is found to reduce the density of PVC to less than 1.39; for example 1.37 or less, such as 1.35 g cm3.

Extrusion in step (iii) can be effected by any conventional forming process such as extrusion and injection moulding, especially to form pipe stock.

In accordance with a further aspect of this invention, there is provided a thermoplastic material, especially PVC, extruded, desirably as pipe stock, in accordance with the aforementioned process.

The following Example illustrates the invention.

Example 100 g of PVC resin (as a suspension ex ICI Ltd) was blended with the following additives: 2 g of tribasic lead sulphate and 2 g of glyceryl monostearate in a high speed biender for 4.5 minutes. This blend was then added to 100 g of tetrahydrofuran which was extracted at 50"C for 6 hours.

The swollen PVC was then added to the hopper of an extruder and pipe was produced therefrom at 1 80 C.

The swollen PVC resin can also be pre-processed by rolling through a roller distance less than the size of the resin particles, i.e. about 10 ,am. The temperature of the rollers should be just above the Tg of PVC (85"C). This helps to remove the remaining solvent and also modify the processing properties, resulting in a tougher product.

Claims

1. An improved process for the production of a non-cellular thermoplastic polymeric material, which process comprises: (i) contacting the non-cellular thermoplastic polymeric material with a swelling agent therefor; (ii) removing at least a portion of the swelling agent to provide a non-cellular thermoplastic polymeric material of reduced density and/or different micromorphology; and thereafter (iii) extruding the non-cellular thermoplastic polymeric material of reduced density and/or different micro-morphology.

2. A process according to Claim 1 wherein the thermoplastic polymeric material comprises a polyolefin, a polyacetal or a halogenated polyolefin.

3. A process according to Claim 2 wherein the halogenated poly-olefin comprises PVC.

4. A process according to any preceding claim wherein the swelling agent comprises a liquid having both a solubility parameter, 8, which differs from that of the thermoplastic polymeric material by less than 5 cal; ml-t and an interaction parameters X, which is less than 1.

5. A process according to any preceding claim wherein the thermoplastic polymeric material comprises PVC and the swelling agent comprises tetrahydrofuran.

6. A process according to any preceding claim wherein in step (i) the contacting is effected at a temperature from O"C to 50"C.

7. A process according to any preceding claim wherein the thermoplastic material comprises PVC and at the end of step (ii) the density is less than 1.39.

8. A process according to any preceding claims wherein the extrusion forms pipe stock.

9. A thermoplastic material formed in accordance with the process of any preceding claim.

10. PVC formed in accordance with the process of any of Claims 1 to 8.

11. Pipe stock formed in accordance with the process of any of Claims 1 to 8.