ITMI951638A1 - LOW PERMEABILITY POLYOLEFIN COMPONENT - Google Patents

Abstract

A hollow polyolefin component is made available selected from pipes and pipe fittings for the transport of non-polar fluids, wherein at least the internal surface of said component is fluorinated to resist permeation by non-polar fluids. A method is also described for treating a hollow polyolefin component to reduce the permeation of the component by non-polar fluids, wherein said method comprises fluorination at least of the internal surface of the aforementioned component.

Description

DESCRIPTION of the patent for industrial invention

This invention relates to hollow polyolefin components selected from pipes and pipe accessories; moreover, the invention relates to a method for treating such components to reduce their permeability to non-polar fluids.

According to the present invention, a hollow polyolefin component is provided selected from pipes and pipe fittings that are used for the transport of non-polar fluids, said component having an internal surface and an external surface, and at least the internal surface of said component being fluorinated to resist permeation by non-polar fluids.

Typically the polyolefin material is polyethylene (PE) of suitable density, such as high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra high molecular weight polyethylene (UHMWPE) or their mixtures, polypropylene (PP), ethylene / propylene copolymers, or mixtures or mixtures of said polyolefins. In other words, the polyolefin can be selected from polyethylenes, polypropylenes, copolymers of ethylene and propylene and mixtures of said polyolefins.

The non-polar fluids for the transport of which the components of the invention are intended include hydrocarbons, in particular gasoline or gasoline, which hydrocarbons can exist in the form of liquids or vapors. By pipe accessories, in contrast to the term pipes, we mean elbows, T-portions, brackets, joints, crossings and, more generally, the types of pipe accessories that are used together with pipe sections to create a duct or a distribution system for fluids, such as for example those pipes and accessories that can be connected by means of electrofusion welding.

Conveniently, both the internal and external surfaces of the component are fluorinated, and each of said fluorinated surfaces can comprise a layer having a fluorine concentration (surface density) of 1 500 μg / cm <2>, preferably 10 - 100 μg / cm < 2> and typically 20 - 60 μg / cm <2>.

According to another aspect of the present invention, a method is made available for treating a hollow polyolefin component selected from pipes and pipe fittings having an internal surface and an external surface, to reduce the permeability of the component by non-polar fluids, where this method comprises the fluorination of at least one internal surface of the component.

The polyolefin of the component can be chosen from polyethylenes, polypropylenes, copolymers of ethylene and propylene and mixtures of said polyolefins, the fluorination intervening both for the internal surface and the external surface of the component, to provide the component with internal and external surfaces in which each comprises a fluorinated layer having a fluorine concentration of 1 - 500 μg / cm <2>.

Preferably, the fluorination takes place by exposing the component to be fluorinated to a fluorine-containing atmosphere, such as a fluorine-containing gas at a pressure of 1-500 kPa, preferably 5-150 kPa, for example 30-80 kPa, and at a temperature at above 0 ° C, and below the melting point of the component material, typically 20 - 100 ° C, for example 30 - 70 ° C. The fluorine-containing gas can be the same fluorine (F2), it can be a fluorinated noble gas such as XeF2, or it can be a fluorohalogen such as ClF3, BrF5, IF7 or the like. The fluorine-containing gas can form part of a mixture with other gases, such as sulfur oxides, nitrogen oxides or carbon oxides, halogens, interhalogens, nitrogen, oxygen, ozone or mixtures thereof, such as air. The proportion of the gas containing fluorine can constitute from 0.1 to 99.9% in terms of volume of said mixture, typically constituting 1-30% of its volume, for example 10 - 20%. Particularly preferred gas mixtures include those which contain 5-20% by volume of fluorinating gas such as F2 and 5-95% by volume of nitrogen such as N2.

In particular, fluorination may comprise exposing each surface of the component to be fluorinated to a fluorine-containing atmosphere comprising 1 to 30% by volume of fluorine and 5 to 95% by volume of nitrogen at a pressure equal to 5 - 150 kPa and at a temperature of 20 - 100 ° C. The duration for which the exposure takes place will be determined by the degree of surface fluorination required for the component. It is expected that routine experimentation will be employed, for each particular case, to determine an optimal or at least acceptable set of parameters, referring to compositions of fluorinating gases, and their pressures and temperatures, for a particular olefin, so to obtain desired values of surface fluorine content.

The fluorination will usually take place in a reactor comprising a vacuum chamber, said reactor being equipped with a gas supply and exhaust, a pressure control, a temperature control and a composition control of the gas mixtures. present there. The method will typically be conducted in a discontinuous manner.

The method may comprise, before exposing the component to the fluorination atmosphere, the degreasing step of at least the internal surface of the component and preferably both its internal and external surfaces.

Suitable degreasing agents which can be used to degrease the inner or outer surfaces of the component prior to fluorination can be selected from trichlorethylene, acetone, ethanol, methylethylketone and xylene. Instead of these, or in addition to these, water-soluble detergents can be used. Once again, routine experimentation will be used to determine which degreasing agents are compatible with the surfaces of the component, and are suitable for the present invention. One combination that the depositor found to be useful is to wash the aforementioned surfaces with a hot aqueous solution of TEEPOL, followed by wiping the washed surfaces with a soft paper towel moistened with pure ethanol. The depositor found that after such a degreasing operation the surfaces should be allowed to dry before being fluorinated.

Consequently, the degreasing operation can comprise the use of a degreasing liquid to remove the grease from the surface to be fluorinated, where the method includes the drying step of this surface after its degreasing, so that the fluorination of the aforesaid surface occurs in dry conditions.

The invention extends to a hollow polyolefin component selected from pipes and pipe fittings for the transport of non-polar fluids, when it is treated in accordance with the method described above.

The pipes and pipe fittings in question are expected to be used in the construction of pipes for the bulk transportation of non-polar fluids such as gasoline or gasoline in the form of liquid or vapor. Such pipes will typically consist of pipe sections, each having a length from 1 to 12 meters, an internal diameter of 25 - 500 mm and a wall thickness of 2.2 - 55 mm, where the polyolefin in question is a polyethylene with high density pigmented, normally black and containing the usual additives or modifying substances.

The invention will now be described, by means of non-limiting illustrative examples, with reference to the following tests conducted by the applicant. The gasoline used for the tests had an octane number of 93, with summer gradation from high altitude, with lead and without alcohol, obtained from a petrol station of Engen Petroleum Limited in the Gauteng province of South Africa.

Tests were conducted to compare the permeation properties with respect to the permeation of liquid gasoline, and the dimensional swelling of the non-fluorinated (control) HDPE pipe with those of a similar HDPE fabric that was fluorinated on the surface in accordance with this. invention.

Each sample was a GM-5010 based black pigmented HDPE tube (Type 4, Class 10, Outside diameter = 110mm, inside diameter = 89mm) supplied by Mega Pipe, a division of Mega Plastics. The total exposed length of each tube was 495mm and the GM-5010 HDPE material was obtained from Hoechst (South Africa) Proprietary Limited.

The following procedure was followed to fluorinate the internal and external surfaces according to the present invention:

First, the tube was degreased by (a) washing with a warm aqueous solution of TEEPOL detergent obtained from Shell Chemical Division (b) scrubbing the surfaces with a soft paper cloth moistened with pure ethanol.

After allowing the tube to dry under atmospheric pressure and temperature conditions for an approximate period of 24 hours, the tube was mounted in a 12.6 liter reactor which was then vacuum sealed. The reactor was subsequently evacuated down to an absolute pressure lower than 0.1 kPa, then loaded with a 100 kPa load of dry nitrogen gas at atmospheric pressure and once again evacuated at a pressure lower than 0.1 kPa. After that, a 10% mixture of F2 / N2 (i.e. a mixture of F2 / N2 comprising 10% by volume of F2) was charged into the reactor, which had been preheated to 50 ° C, at a absolute pressure sufficient to provide the appropriate stoichiometric amount of F2 in the reactor. The fluorination reaction was allowed to proceed for the time required at this temperature before evacuating the reactor and removing the tube. In this way, the tube was fluorinated to a desired surface concentration of, for example, 30, 60, 120 or 150 μg F / cm <2>. Reference was made to the term single treatment to indicate a treatment that provided a surface fluorine concentration equal to 30 μg F / cm <2>, to the term double treatment to indicate a treatment that provided a surface fluorine concentration equal to 60 μg F / cm <2>, at the end quadruple treatment to indicate a treatment that provided a surface fluorine concentration equal to 120 μg F / cm <2> and at the end quintuple treatment to indicate a treatment that provided a surface fluorine concentration equal to 150 μg F / cm <2>.

For the liquid gasoline permeation tests, each of the two pipe sections was sealed at both ends by threading each of the external ends by machine so as to be able to place aluminum screw-on caps on them. In addition, each end of the lengths of pipe has been machined up to a radius of 3 mm to facilitate a high pressure seal at the mating faces of the metal plug and the end of the pipe. Each of the two pipe sections (sealed with a cap at one end and preheated to 50 ° C) was filled to the brim with petrol, which was also preheated to 50 ° C. After that, the open ends were sealed and the complete units were placed in a constant temperature oven at 50 ± 1 ° C. Periodic mass loss measurements were subsequently taken for each sample.

In the following examples, the results which are illustrated in the attached drawings have been obtained, of which:

Figure 1 is a diagram, for HDPE pipes treated according to the invention, and for similar but untreated comparison pipes, in which the permeation is reported in mg / cm <2> as a function of the time expressed in days;

Figure 2 is a diagram, similar to Figure 1, for HDPE pipes treated differently according to the present invention;

Figure 3 is a diagram, similar to Figure 1, for additional treated and untreated HDPE pipes.

EXAMPLE 1

Two tubes of the type described above were subjected to a single fluorination treatment according to the treatment method described above to obtain a surface concentration of fluorine equal to 30 μg F / cm <2>, and the permeation of gasoline through them was tested with the test method described above, while comparing two control tubes that were identical but not fluorinated. The results are shown in Figure 1.

EXAMPLE 2

Example 1 was repeated with the exception that the permeation test of the control tubes was omitted, and in addition to the fact that the two fluorinated tubes were subjected to a single fluorination treatment, two more duplicate pairs of tubes have been tested after having been subjected respectively to a double treatment sufficient to obtain a surface concentration of fluorine equal to 60 μg F / cm <2>, and to a quadruple treatment sufficient to obtain a surface concentration of fluorine equal to 120 μg F / cm <2>. The results are shown in Figure 2.

EXAMPLE 3

Example 1 was repeated, except for the fact that a fivefold fluorination was carried out, sufficient to obtain a surface concentration of fluorine equal to 150 μg F / cm <2>. The results are shown in figure 3.

The results summarized in Figures 1-3 are listed in the following tables, Table 1 and Table 2. Table 1 lists the results of the average permeation of petrol (in mg of petrol / cm <2>) for a single fluorination treatment ( 36 minutes), for double treatments, for quadruple treatments and for controls on untreated elements, while table 2 shows the average results for quintuple treatments and for controls on untreated elements.

Table 1

TABLE. 2

As far as example 3 is concerned, it should be noted that, before exposing it to gasoline, the tube had an average external diameter of 110 mm. After 95 days, the dimensions of the diameter of the tubes of Example 3 were as indicated in Table 3 below.

TABLE 3

These results coincide with those that would have been expected given the permeation data listed above. In this regard, it should also be noted that relative tests conducted on Hoechst HDPE GM7650 have shown that it undergoes a linear dimensional increase of about 8% at 50 ° C when it is fully saturated with the gasoline in question, in a manner not unlike the table. 3, so that Hoechst HDPE GM5010 in tube quality is expected to behave in a similar way in this respect.

The data obtained by the applicant for a test period of 6 months (184 days), including examples 1 and 2, indicate that the permeation rates for control tubes and for tubes of the type treated as above with single fluorination treatments, double and quadruple, are as listed in table 4.

TABLE. 4

Table 4 lists average results, firstly, for the complete 184-day test period and, secondly, for the steady-state phase which is reached some time after the start of each test, when the internal of the HDPE pipe material became completely saturated with gasoline and fully dilated. The steady-state results appear, of course, to be worse than the average results for the entire period, but are more realistic as far as long-term permeation is concerned. In the case of example 3, for an even longer period of time than 272 days, the average permeation rate for a quintuple fluorination treatment was equal to 1.46x10 <-2> mg of gasoline / cm <2> / g, and the steady state rate was 2.09x10 <-2> mg of gasoline / cm <2> / g. These results were slightly worse than those obtained for the quadruple treated tubes in Table 4, although this is believed to result from a slight leak in the sealing mechanism used in Example 3. It should be further taken into account that several factors can affect permeation rates, such as:

temperature;

type or quality of the polyolefin;

degree of crystallinity of polyolefin

molecular nature (size, mass and / or shape of the permeating fluid)

wall thickness of the pipe;

solubility of the permeating fluid in the polyolefin; thickness of the fluorine-containing layer / surface density (μg F / cm <2>);

pressure drop across the pipe wall; and degree of plasticization of the polyolefin.

The depositor is not aware of performance standards regarding the permeability of the pipe for the transport of gasoline in pipelines. It should be noted, however, that the present invention decreases by a significant amount the gasoline permeability of HDPE pipes under test, as is clear from the results of the examples, to the extent that the tested pipes exceed certain performance standards. national and international requirements for low gasoline permeability in vehicle fuel tanks and fuel dispenser pipes. It should also be noted that the tests were carried out at 50 ° C, which is a very high and unfavorable ambient temperature. Substantially better results are expected at lower ambient or test temperatures, such as 30 ° C or less.

Claims (12)

CLAIMS 1. A hollow polyolefin component selected from pipes and pipe fittings that are used for the transport of non-polar fluids, said component having an internal surface and an external surface, and at least the internal surface of said component being fluorinated to resist the permeation by non-polar fluids. 2. A component according to claim 1, characterized in that the polyolefin is selected from polyethylenes, polypropylene, copolymers of ethylene and propylene and mixtures of said polyolefins. 3. A component according to claim 1 or 2, characterized in that both the inner and outer surface of the component itself are fluorinated. 4. A component according to any one of claims 1 to 3, characterized in that each of said fluorinated surfaces comprises a fluorine-containing layer having a fluorine concentration of 1 - 500 μg / cm <2>. 5. A method of treating a hollow polyolefin component selected from pipes and pipe fittings having an internal surface and an external surface, to reduce the permeation of the component by non-polar fluids, said method comprising the fluorination of at least the internal surface of the component. 6. A method according to claim 5, characterized in that the polyolefin of the component is selected from polyethylenes, polypropylene, copolymers of ethylene and propylene and mixtures of said polyolefins, the fluorination being both of the internal surface and of the external one of the component itself, to provide the aforementioned component with an internal and external surface each comprising a fluorinated layer with a fluorine concentration of 1 -500 μg / cm <2>. 7. A method according to claim 5 or 6, characterized in that the fluorination comprises exposing each surface of the component to be fluorinated to an atmosphere containing fluorine comprising from 1 to 30% fluorine by volume and from 5 to 95% of nitrogen in terms of volume, at a pressure of 5-150 kPa and at a temperature of 20-100 ° C. A method according to any one of claims 5 to 7, characterized in that it includes the step of degreasing at least the internal surface of the component, before exposing the component to the fluorination atmosphere. A method according to claim 8, characterized in that the degreasing comprises using a degreasing liquid to remove the grease from each surface to be fluorinated, the method comprising the step of drying each of said surfaces after degreasing, so such that the fluorination of said surface occurs in dry conditions. 10. A hollow polyolefin component selected from pipes and pipe fittings, if treated according to the method of any one of claims 5-9 or 12. A component according to any one of claims 1-4 or 10, substantially as described herein. A method according to any one of claims 5-9, substantially as described herein.