RU2481951C1 - Method of making polymer tape from secondary polyethylene terephtalate - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to production of polymer tape from secondary polyethylene terephtalate suitable for use as edge tape in making seamless 3D geoweb, etc. In compliance with this invention, amorphous crystalline wastes of polyethylene terephtalate are mixed with 0.1-1.0 wt % of 1,3-phenylene-bis(2-oxazoline). Produced mix is extruded at residual pressure, preferably, 8.0-8.5 kPa and extrusion temperature distributed among the zones: I-III zones - 250-260°C, IV-X zones - 255-265°C, XI main zone - 200-210°C. Produced strand is cooled, pelletised and dried at 150±2°C to residual humidity of not over 0.02% and pellets are extruded at: I zones - 245-255°C, II, III zones 265-275°C, IV zone - 255-265°C, V main zone - 240-250°C with subsequent tape forming by calendaring at three-roll calendar cooled by running water circulated inside the rolls.

EFFECT: better mechanical properties.

3 cl, 1 tbl, 1 ex

Description

The invention relates to the production of a polymer tape from secondary polyethylene terephthalate (VPETF), suitable for use as a border tape as a basis for the production of a seamless volumetric geogrid, etc.

It is known that during the extrusion of PET waste, the latter is destroyed. The decrease in the molecular weight of the polymer is due to the presence of moisture in the waste, which causes hydrolysis of the polymer during extrusion, which cannot be completely removed by drying, and an increase in the content of end groups (mainly carboxyl and hydroxyl) in the secondary raw material compared to the primary material.

Known methods for producing granular PET from recycled materials, aimed at increasing the thermal stability of secondary PET, improving the resistance of the secondary material to depolymerization during exposure to the material at elevated temperatures developed during the extrusion of PET during its processing, by increasing its molecular weight. They provide for the extrusion of a mixture of PET waste at a temperature of 260-320 ° C in the presence of functional additives:

- anhydrides of organic dicarboxylic acids, for example maleic, phthalic, methyltetrahydrophthalic, succinic, etc. (ed. certificate of the USSR 567309, C08J 11/06, publ. 1993);

- phenyl ethers of (di- and triphenyl) inorganic acids, for example diphenyl carbonate, triphenyl ether orthophosphoric acid, and esters of polybasic inorganic acids and substituted phenol-tricresylphosphite, triethylphenylphosphite, tri-ortho-chlorophenylphosphite, tri-p-triphenyl n-octyl phenyl phosphate (ed. certificate of the USSR 567309, C08J 11/06, publ. 1993);

- diphenyl esters of dicarboxylic acids, in particular 4,4-diphenyl oxide dicarboxylic acid and adipic acid (ed. certificate of the USSR 603650, C08J 11/04, publ. 1978).

The granular secondary PET obtained in accordance with the considered technical solutions from PET-waste fibers and films can be used both as an additive to the feedstock in the production of fibers and films, and as an independent material. In the named auth. testimonial. in each case, waste from one specific production is used and the technology for producing granules provides for mandatory drying.

The process of solid-phase polymerization (TFP) of PET waste in relation to the manufacture of secondary PET based polymer tapes was actively developed by the United States Illinois Tool Works Inc. from 1997 to 2000 and is protected by a block of patents, including in Russia:

The first of these is US patent 5886058, filed February 3, 1997, No. 794538, as well as the subsequent three patents of this block, pertain to direct DFT of a heterogeneous mixture obtained by co-grinding a mixture collected from primary or secondary PET waste, including many heterogeneous components such as flakes and lumps and having a wide range of characteristic viscosity [η], mainly from 0.60 to 0.80 dl / g with a difference in these values of at least 0.2. As a result of DFT, a heterogeneous material was obtained having an average value [η] of at least 0.85. Subsequently, it is subjected to pressure rolling and subsequent extrusion into a material with [η] of at least 0.90 dl / g, but in the range from 0.90 to 1.5 dl / g.

In the following patents of the company US 6284808 and US 6288131, filed simultaneously October 13, 1998, the authors improve the previous development to increase efficiency and reduce the time of the production process due to:

- removal of PET waste from an inhomogeneous mixture, including substantially crystalline segments of flakes and substantially non-crystalline segments (lumps) of the latter, capable of rapid crystallization during the process with the generation of a significant amount of crystallization heat, which increases the temperature of the process and impairs the fluidity of the mixture;

- clarification of differences in the values of the intrinsic viscosity of the collected starting material: they should be at least 0.05 dl / g, better than 0.10 dl / g and can be in the range of 0.10-0.30 dl / g.

Patent US 6376563, filed December 26, 2000, actually sums up the results of previous publications, excluding some previously made clarifications (enlarged claims) and focusing on the production of polymer tapes. Ultimately protected:

- the process of forming a mixed PET material suitable for further processing, including collecting PET materials with a wide range of [η] values (0.60-0.80 dl / g), co-grinding into a heterogeneous mixture with the removal of substantially non-crystalline segments, due to which prevents the generation of heat of crystallization in the process of further increasing the value [η];

- a process for the production of PET material comprising the above steps and, optionally, the stage where the resulting heterogeneous mixed PET material including only substantially crystalline segments is subjected to a DFT process to produce a heterogeneous material having an increased average value [η] of at least 0 90 dl / g, in the range of 0.90 to 1.5 dl / g;

- the process of forming a PET material suitable for the production of polymer tapes with high characteristics, including the extrusion process to obtain the tape.

The patent specification describes suitable industrial equipment (“destoner”, for example, Forsberg G-4 Sorter or Forsberg P-6R Vacuum Destoner) for removing substantially non-crystalline segments to convert the remaining mixture into fully crystalline material or segments. Such a mixture, excluding undesirable heat of crystallization, can increase [η] in a relatively short time, prevent the tendency of the material to stick together, agglomerate and clog the equipment.

In the description section “Detailed Description of the Preferred Embodiment”, it is noted that after the flakes are passed through the feed hopper and hopper structures of the first and second stages of the DFT process, the product is removed from the hopper of the second step of the DFT and directly goes hot to the feed hopper of the extruder, from which the tape with high characteristics should be made. The supply of the hot product directly from the second stage of the DFT to the tape-producing extruder is economically viable, because conserves a significant amount of heat of the polymer material and, accordingly, reduces the energy requirement per mass of extrudable polymer.

All Patents Pending by Illinois Tool Works Inc. based on the use of material collected from one or more sources, including former and unused PET, which may contain various impurities, mainly PVC, so they all include techniques aimed at removing these impurities and by-products, for example, HCl formed during the process of destruction of PVC, incl. separation of impurities in the flotation apparatus, the treatment cycle of the inhomogeneous mixture with nitrogen in the absence of oxygen, combined with the phase of thermal transfer. When describing the prior art, the authors did not consider these features, because as initial waste, the authors used secondary PET bottle supplied by Clean City LLC and Expert LLC, which does not contain PVC impurities.

Formally, each of these patents can be taken as a prototype, because in technical essence, they are equally close to the proposed solution. The common features are those related to the purpose of the objects, the use of PET waste with a wide initial [η] interval and the manufacture of the tape by extrusion as the initial heterogeneous mixture.

Nevertheless, the solution for the patent US 5886058, because it is this development that has been patented in Russia - patent RU 2151154, C08J 11/04, 5/08; C08G 63/183, C08L 67/02, claimed 02.02.1998, priority US 03.02.1997, publ. 06/20/2000. In it, as the main object (among other objects), a method for producing a polymer tape from recycled PET is claimed, which consists in collecting PET waste, including a heterogeneous mixture of PET waste containing minor amounts of other impurities (mainly PVC) in the form of flakes (crumbs) and lumps with an initial characteristic viscosity (within a wide range of molecular weight distribution) in the range from 0.60 dl / g to 0.80 dl / g, co-grinding the mixture, molding it into a heterogeneous mixture, drying at a temperature of 270-352 ° F (132.22-177.78 ° C), unloading through compression rollers and removing browned PVC particles to obtain a product that is subjected to two-stage polymerization, followed by extrusion and the formation of the tape.

The method provides a tape with high tensile strength and weldability, achieved, as the authors indicate, "not due to the narrow range of characteristic viscosity of the manufactured product, but due to the average final characteristic viscosity of at least 0.80 dl / g" (p. 10 formulas), 0.90 dl / g (p. 12 of the formula) and from 0.90 to 1.5 dl / g (p. 11 of the formula). At the same time, the product obtained as a result of the second stage of DFT, i.e. having an average intrinsic viscosity of 0.95 dl / g, but in the range of 0.7-1.5 dl / g.

The specific values of the operational characteristics are not given in the patent, however, the need to perform DFT, which is the basis of the process, carried out in two stages (Stage I - heating the chips in the absence of oxygen in the presence of nitrogen until the temperature reaches ~ 420-470 ° F or 215.56-221, 11 ° C; removing the heated mixture from the hopper and directing it to another hopper; stage II - temperature ~ 380-425 ° F or 193.38-218.33 ° C - the treatment cycle of the crumb with nitrogen in the absence of oxygen for about 4 hours) , makes the process of obtaining the tape long, complex and energy intensive.

It should be noted that the description of the invention does not contain specific examples of the process technology, and only one graph (figure 3) presents not the results obtained but the “expected results”.

Among the main operational characteristics of the tape used in the manufacture of blanks for the production of volumetric seamless geogrids used to equip crush-resistant lawns and ecological parking lots are tensile strength and elongation at break.

The technical problem of the invention is to develop a process for producing a tape based on secondary PET with increased tensile strength and elongation, suitable, in particular, for the manufacture of products such as border tape and seamless geogrid, which do not require particularly high operational characteristics.

This object is achieved by the fact that in the method of producing a polymer tape from secondary polyethylene terephthalate containing a heterogeneous mixture of polyethylene terephthalate waste with an initial characteristic viscosity in the range of 0.60-0.80 dl / g, melt extrusion and tape formation, amorphous crystalline polyethylene terephthalate waste is used as the initial waste. which are mixed with 0.1-1.0 wt.% 1,3-phenylene bis (2-oxazoline) (TSF), the mixture is extruded into a strand under vacuum, the resulting strand is cooled, granulated, dried When a temperature of 150 ± 2 ° C and residual humidity not more than 0.02%, and extruded pellets, followed by formation of tape calendering.

In this case, the extrusion of a mixture of amorphous-crystalline wastes of polyethylene terephthalate with 1,3-phenylene bis (2-oxazoline) is carried out at a residual pressure of 8.0-8.5 kPa and at a temperature in the zones: I-III zone 250-260 ° С, IV-X zone is 255-265 ° С, XI head zone is 200-210 ° С, and the temperature regime of granule extrusion into zones is: I zone 245-255 ° С, II, III zone 265-275 ° С, IV zone 255- 265 ° C, V head zone 240-250 ° C.

Calendering is preferably carried out on a three-roll calender cooled by running water circulating inside the rolls.

Secondary PET bottle is used as the starting material for the production of the tape, characterized by the following indicators: characteristic viscosity 0.6-0.8 dl / g, melting point - 247 ° C, mass fraction of water 0.46%, bulk density - 300 kg / m ³ , the content of COOH groups - 4.7 mg KOH / g, impurities of PVC and polyolefins are absent.

Material testing was carried out in accordance with the documentation below:

GOST 21553-76. “Plastics. Methods for determining the melting temperature ";

ISO 1628-5 “Plastics. Determination of viscosity number and limit viscosity number. Part 5. Homopolymers and copolymers of saturated polyesters ";

GOST 18249-72 "Plastics. Method for determining the viscosity of dilute polymer solutions ";

GOST 11262-80. “Plastics. Tensile Test Method. "

The invention is illustrated by examples 1-3.

Example 1

In the first stage of extrusion, a secondary polyethylene terephthalate bottle with the characteristics described above is mixed without preliminary drying with 0.5 wt.% 1,3-phenylene bis (2-oxazoline), loaded into an extruder hopper (Labtech Scientific type LTE-20-40 Labtech Engineering Company LTD), which is equipped with a vacuum degassing system. The twin-screw batcher mix is fed into the extruder with a screw diameter of 20 mm, a ratio of the length L and the diameter D of the screws 40.

Technological mode of extrusion.

The temperature regime of extrusion in the zones: I-III zone 250-260 ° C, IV-X zone 255-265 ° C, XI head zone 200-210 ° C.

Screw speed 200 rpm.

Dispenser screw rotation speed 40 rpm.

The residual pressure is 8.0-8.5 kPa.

The strand emerging from the extruder head is cooled in a bath of cold water (water temperature 10-50 ° C, preferably 15-40 ° C) and fed to the granulator. The obtained granules are dried in a vacuum oven at a temperature of 150 ± 2 ° C to a residual moisture content of not more than 0.02% and sent to the second stage of extrusion into the extruder hopper, and from it into a single-screw extruder with a screw diameter of 33 mm, ratio L / D 30 equipped with a flat-slit head through which the polymer melt is pressed onto a three-roll calender. The temperature of the water circulating inside the rolls is 15-20 ° C. The resulting tape at a speed of 2 m / min is wound on a drum.

Technological mode of extrusion of the tape.

The temperature regime of extrusion: I zone 245-255 ° С, II, III zone 265-275 ° С, IV zone 255-265 ° С, V head zone 240-250 ° С.

Screw rotation speed 100 rpm;

The frequency of rotation of the rolls is 42 m / min.

The tapes of examples 2, 3 were obtained using a technology similar to example 1, but using boundary quantities of TSF (the upper limit is 1.0% and the lower limit is 0.1%).

The characteristics of the obtained tapes are presented in the table, which for comparison shows the characteristics of the tape obtained from primary polyethylene terephthalate without the addition of TSF.

Table Characteristics of the tape (thickness 1.5 mm) TSF content, wt. % PET (control) one 2 3 0.5 0.1 1,0 0 Characteristic viscosity, dl / g 0.85 0.73 0.85 0.77 Temperature melting ° C 246 246 246 245 Residual crystallinity,% fifteen twenty fifteen 26 Yield strength tensile, MPa 53 45 54 42 Relative elongation in tension,% 377 350 380 348

From the information presented in the table it follows that for a 1.5 mm thick VPETF tape, the residual crystallinity is 15% versus 26% for a tape of the same thickness from primary PET; in this case, the tensile strength increases by 26%; (53 MPa versus 42 MPa), the relative elongation in tension - by 8% (377% against 348%).

The presence of crystallinity increases the risk of destruction of the film [Production of packaging from PET. David Brooks, Jefer Giles, St. Petersburg, Profession, 2006, p.199], in connection with which the decrease in residual crystallinity is of particular importance. According to the invention, for a calendered film, the residual crystallinity is reduced from 26% to 15%, i.e. there is an improvement of 58%.

PET is highly hygroscopic in nature and absorbs moisture very quickly to a saturation level; raw materials are usually dried very thoroughly before processing. Increased crystallinity should lead to a decrease in the amount of water present, and there is a proportional relationship between the absorption of water and the volume of the amorphous fraction [Production of packaging from PET. David Brooks, Jefer Giles, St. Petersburg, Profession, 2006, pp. 93-94]. Since an amorphous-crystalline polymer is used as the initial VPETF, in which the water content will be increased, the possibility of the extrusion process at the first stage without preliminary drying seems to be an unobvious effect.

The intrinsic viscosity value for the resulting tape is 0.85 dl / g, i.e. exceeds this indicator for the tape from primary PET by 25%, which also confirms the non-obviousness of the development.

Regarding the use of TSF in combination with PET, it is known that TSF is used:

- for lengthening the chain of polyesters, in particular PET (Journal of Applied Polymer Science, 32, 1986, 5193-5202; Polym. Prepr., 1998, 29 (1), 567-570);

- as thermal stabilizers, incl. while improving mechanical properties (US 3959215, publ. 1976; adding to the granules of PET before spinning fibers);

- as crosslinking agents (JP 63248852 A, publ. 1988);

- as agents that improve processability (JP 63118360, publ. 1988; JP 62230844 A, publ. 1987; JP 0258557 A, JP 0258558, JP 0258561, publ. 1990);

- as agents that improve the compatibility of thermoplastics used in the preparation of molding compositions (US 5378765, publ. 1995);

- in a continuous process for reactive combination of polymers, including the interaction of bisoxazoline with one or more of the first polymer in a ratio of 1: 2 to 1: 6 with the formation of a polymer reactive at elevated temperatures, followed by the addition of the latter to the second polymer (one or more). Moreover, the reactive polymer includes at least 5 wt.% Chemically unbound bisoxazoline (US 7847031, publ. 2010).

The authors did not identify sources in which the TSF would be used in the processing of PET bottle waste into a high-quality product suitable for the production of polymer tapes from it, nor the information on the influence of the TSF on the crystallization process of VPETF waste. The studies conducted by the authors showed that the introduction of TSF additives in an amount of 0.1-1.0 wt.% By 25% reduces residual crystallinity.

Claims (3)

1. A method of obtaining a polymer tape from a secondary polyethylene terephthalate containing a heterogeneous mixture of polyethylene terephthalate waste with an initial characteristic viscosity in the range of 0.60-0.80 dl / g, melt extrusion and tape formation, characterized in that amorphous waste is used as the initial waste. crystalline polyethylene terephthalate, which is mixed with 0.1-1.0 wt.% 1,3-phenylene bis (2-oxazoline), the mixture is extruded into a strand under vacuum, the resulting strand is cooled, granulated, dried at a temperature of (150 ± 2) ° C d residual moisture content of not more than 0.02%, and extruded pellets, followed by formation of tape calendering. 2. The method according to claim 1, characterized in that the extrusion of a mixture of amorphous-crystalline wastes of polyethylene terephthalate with 1,3-phenylene bis (2-oxazoline) is carried out at a residual pressure of 8.0-8.5 kPa and temperature in zones: I -III zone 250-260 ° C, IV-X zone 255-265 ° C, XI head zone 200-210 ° C, and the temperature regime of extrusion of granules in the zones is: I zone 245-255 ° C, II, III zone 265 -275 ° С, IV zone 255-265 ° С, V head zone 240-250 ° С. 3. The method according to any one of claims 1 and 2, characterized in that the calendering is carried out on a three-roll calender cooled by running water circulating inside the rolls.