Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF STARCH BASED POLYESTERS"

Abstract

An improved process for the preparation of starch based biodegradable polyesters which comprises thermally melting and degrading the recycled /degraded polyesters at temperature at 80 to 120° C above the melting point of the said polyester under constant stirring at a rate of 50 to 200 rpm for a period ranging between 10 to 40 minutes, adding starch in the range of 30 to 300%w/w of thermally degraded polyesters and keeping the reaction mixture under above mentioned conditions for a period of 1 to 10 minutes, and quickly removing the material to obtain the starch based polyesters.

Full Text

This invention relates to an improved process for preparation of starch based biodegradable polyesters. More particularly it relates to the process for the preparation of blends of starch and polyesters, and their derivatives. Still more particularly this invention relates to a process for the preparation of blends of starch and degraded or recycled aromatic polyesters to obtain materials that can be used in packaging applications and other low end applications like toys. Several studies have been reported on blends of starch with aliphatic polyesters and polyolefms which can be processed at temperatures below 200° C. It is reported by B A Ramsay, V Langlade, P J Carreau and J A Ramsay in Appl Environ Microbial 59(4), 1242-6 (1993) that wheat starch and poly (p-hydroxybutyrate-co-p -hydroxyvalerate) could be blended at 160 °C with decreased mechanical properties, which were still in a useful range. It has been disclosed in Eur Pat Appl EP 580032 Al dt 26 Jan 1994 (from Chem Abstr 120:219560) that biodegradable molding compositions containing thermoplastics starch and thermoplastic aliphatic polyesters can be made. Studies on blends of a biodegradable thermoplastic "Bionolle" with 5-30% by weight of starch were investigated for the mechanical and thermal properties of their blown films, as reported by J A Ratto and P Stenhouse in Annual Technical Conference -ANTEC, Conference Proceedings Society of Plastics Engineers, Brookfield, CT, USA vol 2 p 1824-1828 (1995). . Earlier reported processes were mainly developed to produce biodegradable materials using starch as a filler and using aliphatic polyesters, for processing at temperatures at which starch does not degrade. Due to poor compatibility of starch with most other plastics, the major focus has always been on compatibilising the blend by use of additives. For example, in the Eur Pat Appl EP 580032 Al dated 26 Jan 1994 referred to in the earlier paragraph, polyglycerin and sodium lactate were added to the starch-aliphatic polyester composite to impart desireable properties. Another drawback of the earlier processes is that the starch percentage in the product is low. In the paper by BA Ramsay, V Langlade, PJ Carreau, and JA Ramsay in Appl Environ Microbiol, 59(4), 1242-6, 1993, it has been shown that increasing the content of starch from 0 to 50% (wt./wt.) considerably decreased the mechanical properties due to the low thermal, elongational and tensile properties of starch. A greater percentage of starch would render the polymer material more biodegradable , more environmentally friendly, and more economically viable. Another disadvantage of the earlier processes is that the process could not be carried out at higher temperatures due to degradation of starch above 250 °C,, thereby making it difficult to process starch with aromatic polymers that have high melting points, such as polyethylene terephthalate. The main object of the present invention is to provide an improved process for preparation of starch based polyesters and other thermoplastics without the use of added compatibilisers. Another object of the present invention is to develop a process for preparing starch polyester blends containing upto 75% of starch by weight. Yet another object of the present invention is to develop a process using degraded or recycled aromatic polyester and other thermoplastics to advantageously utilise the decreased melting points of the degraded/recycled polymers and new functional groups created on these degraded/recycled polymers as a result of the degradation process, in order to enable processing of starch at temperatures at 250° C such that the onset degradation temperature of the blend material produced is around 270° C. The polyesters and their derivatives prepared by the process of the present invention have sufficient thermal stability and are also economically viable since instead of using virgin thermoplastic synthetic polymers, use is now made of degraded/recycled thermoplastic synthetic polymers which are much cheaper, have lower melting points, and are also more reactive with the added starch. Accordingly, the present invention provides an improved process for the preparation of starch based biodegradable polyesters which comprises thermally melting and degrading the recycled /degraded plyesters at temperature at 80 to 120° C above the melting point of the said polyster under constant stirring at a rate of 50 to 200 rpm for a period ranging between 10 to 40 minutes, adding starch in the range of 30 to 300% w/w olthermallv. degraded poly esters and keeping the reaction mixture under above mentioned conditions for a period of 1 to 10 minutes, and quickly removing the material to obtain the starch based polysters In one of the embodiments of the present invention the polyester used may be polyalkelene terephthalate exemplified by polyethylene terephthalate, polybutylene terephthalate and their copolymers and blends, preferably polyethylene terephthalate. In the present invention, a reaction between the end-groups fcarboxvl. hydroxyl) of recycled aromatic polyester with the hvdroxvl of starch occurs. Also, added additives such as 12-hvdroxvstearic acid and glvcerol can react with both starch hvdroxyls as well as aromatic polvester end-groups. Since no particular advantages were observed in terms of increase in onset of degradation temperature of the composition bv the use of 12-hvdroxvstearic acid and glvcerol. which can react in a facile manner with carboxvl and hvdroxvl end-groups of the degraded aromatic polyesters, or the hvdroxyls of starch, it can be inferred that the hvdroxvl groups of starch undergo facile reaction with the end-groups of degraded/recycled PET (aromatic polyesters in general). In the prior art, starch based aliphatic polvester compositions, with and without additives, have been well reported. However compositions based on aromatic polyesters with starch are not reported. In particular, the novelty of using degraded/recycled PET so as to utilise the numerically greater end-groups (as compared to virgin PET) is not reported. Further, use of virgin PET would require much higher processing temperatures due to its higher melting point. Also, using starch in the composition of over 300% of the weight of the aromatic polvester composition with minimal effect on the onset of thermal degradation temperature of the composition (example 5) has also not been reported, nor has the utilization of chemical reaction between the end-groups of the aromatic polyesters and the functional groups of starch. Advantages of the compositions: Degraded/recycled PET is abundantly available and has no economic value. Starch is also a very cheap material abundantly available. Blends of these two materials at a temperature/residence time profile wherein the starch does not degrade significantly but can react with the PET end-groups to give a reaction-incorporated filler system of degraded/recycled PET/starch composite mat is moldable. is a development with potential to be utilised as an industrial packaging material. In another embodiment the starch added may be 30% to 300% by weight of the degraded polyester. The process of the present invention is described hereinbelow with reference to examples which are illustrative only and should not be construed to limit the scope of the present invention in any manner. Example 1 Commercial poly (ethylene terephthalate) (PET) of melting point 257°C was thermally degraded by subjecting it to a temperature of 350°C in a single screw extruder for 20 min at 80 rpm. The melting point of the degraded PET thus came down to 200 °C from 257 °C. 25 g of this degraded PET was melted in the single screw extruded at 250 °C and 25 g of corn starch (moisture content ~10%) was added by mixing at 60 rpm of the screw for 3 min and the material was quickly removed. The thermal analysis of this show onset of degradation temperature to be 267 °C. This material could be molded. Example 2 25 g of recycled/degraded PET of melting point 200°C was taken in a single screw extruder , melted at 250 °C and 25 g of corn starch (moisture content 10%) and 2.5 g glycerol was added, the mixture heated at 250 °C for 3 min at 60 rpm and then was removed. The thermal analysis of this material showed the onset of degradation temperature to be 265 °C and the material was moldable. Example 3 25 g of recycled/degraded PET of melting point 200°C was taken in a single screw exruder , melted at 250 °C and 20 g of corn starchalong with 12-hydroxystearic acid was added, the mixture heated at 230 °C for 3 min at 50 rpm and then was removed. The thermal analysis of this material showed the onset of degradation temperature to be 265 - 270 °C. Example 4 12.5 g of recycled/degraded PET of melting point 200°C was taken in a single screw extruder , and 34.5 g starch along with 3.5 g glycerol was added at 250 °C in a single screw extruder operating at 60 rpm. The material was heated for 10 min. and then removed. The thermal analysis of this material showed the onset of degradation temperature to be 225 °C. Example 5 EXAMPLE -5 10 g of recycled/degraded PET of melting point 200°C was taken in a single screw extruder , heated to 250 °C and 30 g of starch was added, and heated at 250 °C for 3 min then removed. The thermal analysis of this material showed the onset of degradation temperature to be 250 °C We claim: 1. An improved process for the preparation of starch based biodegradable polyesters which comprises thermally melting and degrading the recycled /degraded polyesters at temperature at 80 to 120° C above the melting point of the said polyster under constant stirring at a rate of 50 to 200 rpm for a period ranging between 10 to 40 minutes, adding starch in the range of 30 to 300%w/w of thermally degraded polyesters and keeping the reaction mixture under above mentioned conditions for a period of 1 to 10 minutes, and quickly removing the material to obtain the starch based polyesters 2. An improved process as claimed in claim 1 , wherein the biodegradable polyesters terephthalate , polybutylene terephthalate , their copolymers and blends, preferably polyethylene terephthalate 3. An improved process for the preparation of starch based biodegradable polyesters as fully described hereinbefore with reference to examples contained therin

Documents:

808-del-1999-abstract.pdf

808-del-1999-claims.pdf

808-del-1999-correspondence-others.pdf

808-del-1999-correspondence-po.pdf

808-del-1999-description (complete).pdf

808-del-1999-form-1.pdf

808-del-1999-form-19.pdf

808-del-1999-form-2.pdf