WO2012095861A1

WO2012095861A1 - Method for preparing recycled polyethylene terephthalate

Info

Publication number: WO2012095861A1
Application number: PCT/IN2012/000014
Authority: WO
Inventors: Srinivasacharya Ramacharya Ayodhya; Chetan Vijay Limaye; Kuldip Suryaprakash UPADHYE; Shivamurthy Padadayya JADIMATH; Vikas Kadu Bhangale
Original assignee: Reliance Industries Limited
Priority date: 2011-01-13
Filing date: 2012-01-05
Publication date: 2012-07-19

Abstract

The present invention relates to an improved method for recycling flakes of polyethylene terephthalate or copolyesters thereof comprising the steps of washing and drying of flakes, melting flakes in presence of zinc or tin compound and extruding said molten flakes to obtain final product like amorphous polyethylene terephthalate chips, fibre or filaments. The invention also relates to a final product with improved 'L*' and 'b*' color prepared by the said method. The present invention also relates to improved solid state polymerization rate of recycled amorphous PET chips.

Description

METHOD FOR PREPARING RECYCLED POLYETHYLENE TEREPHTHALATE

FIELD OF THE INVENTION

The present invention relates to an improved method for the preparation of recycled polyethylene terephthalate by recycling flakes of polyethylene terephthalate or copolyesters thereof. More particularly, the present invention relates to a method for recycling flakes of polyethylene terephthalate or copolyesters thereof comprising the step of treating flakes in presence of compound comprising tin or zinc more preferably tin or zinc oxalates. The present invention also relates to a final product with improved 'L*' and 'b*' color. The present invention also relates to improved solid state polymerization rate of recycled amorphous polyethylene terephthalate chips. The present invention also relates to use of various organic or inorganic toners, dyes, optical brighteners and combinations added along with the tin or zinc compounds for further enhancement in color of recycled polyethylene terephthalate chips, fibers or filaments.

BACKGROUND OF THE INVENTION

PET products are widely used, as beverage bottles, containers and jars, for high-grade sheet and -fibers, and in medical supplies, especially syringes and containers for instance. Attempts have been made to include the material in the recycling process as far as possible, but so far without avail in that it has been impossible to entirely decompose residual contaminants in the product. The current commercially employed methods allow the use of PET recyclate only in applications with low-grade demands. Where higher quality is required, as in the manufacture of bottles, a little recycled PET may be blended with a lot more of the non-recycled material. Bottles with tri-laminate walls are also known, the innermost layer blown from non-recycled PET and the core made of the recycled material.

When PET products have to be made entirely of recyclate, the material must contain very low acetaldehyde content, if indeed at all, in the ppm (mg/kg) range. Flakes obtained from PET products are contaminated, mainly with PVC, adhesives used for labels and many other contaminants. These contaminants must be eliminated or entirely decomposed during the recycling process. A method of preparing thermally stressed polyester waste for re-use in the production of high-quality PET's is known from German 4 034 459 Al. The waste is chopped, cleaned, sorted, and recondensed. The chips are melted and the melt is filtered, cooled, and granulated. The solid granulate is recondensed to increase its molecular mass. The condensed granulate is forwarded to an extruder and extruded along with previously unused raw material into sheet, sections, or billets. The solid phase is condensed in a rumble drier at a vacuum of 0.1 mbar for approximately 12 hours at 200-250.degree. C. Essential to this method is the re-use of polyester waste from various sources, and the usual loss of mechanical and optical properties can be extensively compensated by the recondensation.

US Patent 6,436,322 teaches a method for recycling polyethylene terephtalate (PET) flakes, characterized in that the flakes are extruded and granulated under vacuum, after which the granulate is after condensed in a solid phase under vacuum. US Patent 6,770,680 discloses a method for recycling of PET constituents from plastic material including at least plastic beverage bottles comprising the steps of comminuting said plastic beverage bottles to form a mixture of particles containing PET flakes; and washing the PET flakes, said washing comprising simultaneously treating the PET flakes hydraulically and mechanically in at least one washer with a cleaning solution including caustic soda at a temperature of about 75 to 95°C for about 20 to 40 minutes.

The present invention discloses a method for recycling flakes of polyethylene terephthalate or copolyesters thereof comprising the step of treating flakes in presence of compounds comprising tin or zinc. The present invention also relates to a final product with improved 'L*' and 'b*' color. The present invention also relates to improved solid state polymerization rate of recycled amorphous polyethylene terephthalate chips. The present invention also relates to use of various organic or inorganic toners, dyes, optical brighteners and combinations added along with the tin or zinc compounds for further enhancement in color of recycled polyethylene terephthalate chips, fibers or filaments. OBJECTS OF THE INVENTION

It is an important object of the present invention to provide a method for recycling flakes of polyethylene terephthalate or copolyesters thereof comprising the steps of washing and drying of flakes, melting flakes in presence of compounds comprising of tin or zinc and extruding said molten flakes to obtain amorphous chips, fibre or filament through direct spinning.

Another object of the present invention is to provide a method for recycling flakes of polyethylene terephthalate or copolyesters thereof optionally comprising the steps of crystallization of amorphous chips and solid state polymerization of the said crystallized chips.

A further object of the present invention is to provide a method with improved solid state polymerization productivity.

Yet another object of the present invention is to provide polyethylene terephthalate chips, fibers or filaments with improved 'L*' and 'b*' color.

Yet another object of the present invention is to provide an improved recycling method to use various organic or inorganic toners, dyes, optical brighteners and combinations added along with the tin or zinc compounds for further enhancement in color of recycled polyethylene terephthalate chips, fibers or filaments.

SUMMARY OF THE INVENTION

The above and other objects of the present invention are achieved by a method of recycling flakes of polyethylene terephthalate or copolyesters thereof which comprises the steps of washing and drying of flakes, melting flakes in presence of compounds comprising tin or zinc and extruding said molten polyethylene terephthalate to obtain amorphous chips, fibre or filaments. In other words, the present invention relates to a method for the preparation of recycled polyethylene terephthalate or copolyesters thereof with improved color comprising steps of melting flakes of polyethylene terephthalate or copolyesters thereof in presence of at least one compound selected from tin compound or zinc compound and extruding the molten flakes of polyethylene terephthalate or copolyesters thereof to obtain amorphous chips, fiber or filament. The present invention discloses a process optionally comprising the steps of crystallization of amorphous chips and solid state polymerization of the said crystallized chips with improved polymerization rate.

Preferably, said compound is in the form of powder, masterbatch or slurry. Preferably, said tin compound is an inorganic or organic tin compound and said zinc compound is an inorganic zinc compound.

Preferably, said inorganic tin compound is selected from tin oxalate, tin oxide, tin chloride, tin fluoride and combinations thereof.

Preferably, said organic tin compound is selected from Dibenzyltin oxide, Dibutyltin oxide, Dicyclohexyltin oxide ,Didodecyltin oxide, Diisobutyltin oxide Dimethyltin oxide, Di-l-naphthyltin oxide, Dioctyltin oxide, Diphenyltin oxide, Di-o- tolyltin oxide Divinyltin oxide, Dicyclohexyltin dihydroxide , Dibutyltin dihydroxide, Dibenzyltin dihydroxide, Didodecyltin dihydroxide, Dimethyltin dihydroxide, Dioctyltin dihydroxide , Di-o-tolyltin dihydroxide. Didodecyl bis (benzyloxy) tin , Dibutyldibutoxytin, Dimethyldibutoxytin , Dibutyldimethoxytin ,

Dibutyldiphenoxyrin, Dibutyltin (0, 0)-bis (methylricinoleate), onobutyltin trimethoxide , Monobutyltin tributoxide, Monomethyltin trimethoxide, Monomethyltin tributoxide Dibutylmethoxybutoxytin, Dibutyltin ethylene glycoxide and combinations thereof. Said inorganic zinc compound is selected from zinc oxalate, zinc oxide, and combinations thereof.

Preferably, said tin or zinc compound is added in the range of 5 to 5000 ppm, more preferably, in the range of 5 to 500 ppm Preferably, said melting of flakes is carried out between temperature range of 250 to 300°C.

In another preferred embodiment, a method for recycling flakes of polyethylene terephtalate or copolyesters thereof comprising the steps of washing and drying of flakes, , melting flakes at temperature range of 250 to 300°C in presence of compounds comprising tin or zinc, more preferably, tin oxalate or zinc oxalate in the range of 5 to 5000 ppm and preferably, in the range of 5 to 500 ppm, and extruding said molten polyethylene terephtalate to obtain amorphous chips, fibre or filaments, optionally comprising the steps of crystallization of amorphous chips and solid state polymerization of the said crystallized chips is disclosed. In another embodiment of the present invention, a method which improves the solid state polymerization productivity is disclosed.

In yet another embodiment of the present invention, a method which improves 'L*' and 'b*' color of the fibre, filament or chips is disclosed.

In yet another embodiment of the present invention, various organic or inorganic toners, dyes, optical brighteners and combinations can be added along with the tin or zinc compounds more preferably tin or zinc oxalate for further enhancement in color of recycled polyethylene terephthalate chips, fibers or filaments

In yet another embodiment of the present invention, fibre, filament or chips prepared by said method is disclosed.

BRIEF DESCRIPTION OF THE DRAWING

FIGURE 1: A flow chart representing the various steps involved in the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention discloses a method for recycling flakes of polyethylene terephtalate or copolyesters thereof comprising the step of treating flakes in presence of compound comprising of tin or zinc.

The base resin of flakes of polyethylene terephthalate or copolyesters thereof may be produced with various dihydroxyl-containing compounds and di-carboxylic acids or anhydrides or lower alkyl esters in presence of several organic or inorganic catalysts. Preferably, said flakes may be obtained by compressing waste PET co polyester bottles into bales and crushing such bales to flakes.

The flakes are preferably washed at a temperature of 70 to 75°C with caustic and dried.

The said tin or zinc compound, preferably tin oxalate or zinc oxalate may be directly injected during extrusion process of recycling of PET bottle flakes to improve both 'L' and 'b' color of the extruded fibre or chips. The compound addition can be in the range of 5-5000 ppm more preferably in the range of 5-500 ppm depending on the applications of the final product. Various organic or inorganic toners, dyes, optical brighteners and combinations can also be added along with the tin or zinc compounds for further enhancement in color of recycled polyester chips, fibers or filaments The said composition can be subsequently used for improving the solid-state polymerization: rate (thus improving the plant productivity) of extruded amorphous chips to achieve the desire molecular weight required for processing of packaging applications

The present invention also relates to a final product with improved 'L*' and

'b*' color. The compounds comprising Zinc or Tin may also be used during recycling of PET bottles directly in extrusion process to improve both 'L*' and V color of the extruded fibre, filament or chips and subsequently for improving the solid state ^" polymerization rate of extruded amorphous chips to achieve the desired molecular weight. The extent of loading of the compound may be in the range of 5 to 5000 ppm and preferably in the range of 5 to 500 ppm.

The present invention is illustrated and supported by the following examples. These are merely representative examples and optimization details and are not intended to restrict the scope of the present invention in any way.

EXAMPLES-

Comparative (C)

Bottle flakes were washed and dried in vacuum oven at 150°C for 6 hours and then extruded at temperature of 265-280°C in the form of amorphous chips.

These chips were analyzed for intrinsic viscosity, color and carboxyl end groups. These amorphous particles were used as precursor for solid-state polymerization.

Example 1

Bottle flakes were washed, dried at 150°C for 6 hours and mixed with inorganic tin compound (70 ppm) preferably tin oxalate in the form of powder in a high speed mixer and then extruded at temperature of 265-280°C in the form of amorphous chips.

Example 2

Bottle flakes were washed, dried at 150°C for 6 hours and mixed with inorganic zinc compound (120 ppm) preferably zinc oxalate in the form of powder in a high speed mixer and then extruded at temperature of 265-280°C in the form of amorphous chips.

These chips were analyzed for intrinsic viscosity, color and carboxyl end groups. These amorphous particles were used as precursor for solid-state polymerization. Results of amorphous chips

Amorphous Chips data:-

• L* color improved by 1 unit with the addition of inorganic tin or zinc compound · b* color reduced by 3 units with the addition of inorganic tin or zinc compound

• Melt viscosity marginally improved with the addition of inorganic tin or zinc

compound

Solid State Polymerization: -

Amorphous prepolymer particles having IV of 0.6 dl/g obtained according to the examples C, El, E2 were crystallized at 140°C for three hours and then subjected to solid-state polymerization at 205°C (Gas Temperature) for seven hours of residence time under Nitrogen atmosphere to raise the molecular weight in terms of intrinsic viscosity. Solid state polymerization rate calculated in terms of IV rise per hour and color measured on color spectrophotometer of SSPd chips

Significant improvement in SSP reactivity rate observed with the addition of inorganic tin or zinc compound

L* color of the recycled SSP chips significantly improved with the addition of inorganic tin or zinc compound

b* color of recycled PET chips drastically reduced with the incorporation of inorganic tin or zinc compound.

Claims

A method for the preparation of recycled polyethylene terephthalate or copolyesters thereof with improved color comprising steps of melting flakes of polyethylene terephthalate or copolyesters thereof in presence of at least one compound selected from tin compound or zinc compound and extruding the molten flakes of polyethylene terephthalate or copolyesters thereof to obtain amorphous chips, fiber or filament.

The method as claimed in claim \, wherein said flakes are washed and dried before melting.

A method as claimed in claim 1 or 2 wherein said flakes are obtained by crushing waste bottles of PET or copolyesters thereof.

The method as claimed in any of the preceding claims wherein said method optionally comprises the steps of crystallization of amorphous chips at a temperature in the range of 140 to 180°C and solid state polymerization of the crystallized chips.

The method as claimed in any of the preceding claims, wherein said tin or zinc compound is in the form of powder, masterbatch or slurry.

The method as claimed in any of the preceding claims, wherein said tin compound is an inorganic tin compound, preferably, selected from tin oxalate, tin oxide, tin chloride, tin fluoride and organo tin compounds.

The method as claimed in any one of claims 1 to 5 wherein said zinc compound is an inorganic zinc compound, preferably selected from zinc oxalate, zinc oxide and combinations thereof.

8. The method as claimed in any of the preceding claims wherein said tin or zinc compound is added in the range of 5 to 5000 ppm, preferably, in the range of 5 to 500 ppm.

9. The method as claimed in any of the preceding claims wherein said melting of flakes is carried out between temperature range of 250 to 300°C.

10. A method for recycling flakes of polyethylene terephthalate or copolyesters thereof comprising melting the flakes at temperature range of 250 to 300°C in presence of at least one compound selected from tin oxalate or zinc oxalate in the range of 5 to 500 ppm , extruding the molten flakes of polyethylene terephthalate or copolyesters thereof to obtain amorphous chips, fibre or filament, optionally crystallizing said amorphous chips and subjecting said crystallized chips to solid state polymerization.

11. The method claimed in any of the preceding claims, wherein said method improves the solid state polymerization productivity by around 10 to 40% depending upon the loading of tin or zinc compound.

The method claimed in any of the preceding claims, wherein said method improves both 'L*' and 'b*' color of the amorphous chips, fibre or filaments

A recyclate of polyethylene terephthalate or copolyesters thereof with improved color obtained by mixing flakes of polyethylene terephthalate or copolyesters thereof and atleast one compound selected from tin compound or zinc compound

Fibre, filament or amorphous chips as prepared by the method as claimed in any of the preceding claims.