DESC:FIELD
The present disclosure relates to a process for the preparation of polyethylene terephthalate.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which it is used indicate otherwise.
Pre-polymer: The term pre-polymer refers to a monomer or system of monomers that have been reacted to an intermediate molecular mass state. The pre-polymer is capable of further polymerization by reactive groups to a fully cured high molecular weight state.
Extrusion blow molding: The term “extrusion blow molding” also known as EBM refers to a molding process wherein plastic is melted and extruded into a hollow tube (a parison).
Parison: The term “parison” refers to a tube-like piece of plastic with a hole in one end through which compressed air can pass. Alternatively, the term parison refers to an unshaped mass of plastic before it is molded into its final form.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Manufacturing industries such as cosmetics, oil and the like, have a high demand for containers of varied complex shapes and sizes, especially with transparent nature. Containers with different kind of shapes can be produced by the extrusion blow molding (EBM) process.
Polyethylene terephthalate (PET) is widely used in the injection blow molding process. The main of advantages of PET include toughness, clarity, good barrier properties, lightweight, design flexibility, chemical resistance and good shelf-life performance. However standard grade PET is difficult to process using extrusion blow molding due to their relatively low inherent viscosities and high crystalline melting point which lead to low melt strength and low melt viscosity at the processing temperature thereby limiting their applicability to simple shapes.
Therefore, there is felt a process for preparing polyethylene terephthalate that mitigates the herein above mentioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide polyethylene terephthalate suitable for extrusion blow molding.
Another object of the present disclosure is to provide a process for preparation of polyethylene terephthalate suitable for extrusion blow molding.
Still another object of the present disclosure is to provide polyethylene terephthalate having increased intrinsic viscosity, high melt strength, reduced rate of crystallization, lower processing temperature, and comparatively better product clarity.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure provides a process for the preparation of polyethylene terephthalate. The process comprises esterifying terephthalic acid by reacting with monoethylene glycol, to obtain an esterified mixture. The esterified mixture is pre-polymerized by adding a catalyst, a thermal stabilizer and a branching reagent to obtain a pre-polymer. The pre-polymer is polymerized at a temperature in the range of 270 oC to 300 oC, for a time period in the range of 80 minutes to 150 minutes, to obtain a polymeric product comprising polyethylene terephthalate having an intrinsic viscosity of less than 0.65 dL/g. The polymeric product is polycondensed by solid state polymerization at a temperature in the range of 190 oC to 230 oC, for a time period in the range of 8 hours to 24 hours, to obtain polyethylene terephthalate having an increased intrinsic viscosity in the range of 0.85 dL/g to 1.2 dL/g.
In another aspect, the present disclosure provides a polyethylene terephthalate resin characterized by having an intrinsic viscosity in the range of 0.85 dL/g to 1.2 dL/g and crystallinity in the range of 35% to 55%.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates the processing time in the solid state polymerization and the resulting change in intrinsic viscosity for Examples 1-3 and the comparative examples 1 and 2;
Figure 2 illustrates thermal analysis graph for sample 1;
Figure 3(A) illustrates the graphical representation of the change in melt viscosity for the samples with respect to shear rate at 260°C;
Figure 3(B) illustrates the graphical representation of the change in melt viscosity for the samples with respect to shear rate at 280 °C;
Figure 4(A) illustrates the image of blow molded product obtained from PET sample 1; and
Figure 4(B) illustrates the image of blow molded product obtained from PET sample 3.
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Polyethylene terephthalate (PET) is widely used in the injection blow molding process. PET has very good clarity and mechanical properties, however standard PET is difficult to process using extrusion blow molding due to its relatively low melt strength. Also, it requires high processing temperature, which leads to reduction in melt viscosity making it unsuitable for the extrusion blow molding process.
Conventionally, the extrusion blow moldable grade resin has been developed through modification of polymer backbone with linear co-monomers and branched co-monomer. The branched PET thus obtained, has superior melt strength and extensional viscosity compared with linear PET. However, larger degree of branching is not desirable as it results into gels which lead to increase in processing temperature that eventually reduces viscosity of the polymer.
A typical PET material for application in extrusion blow molding would need to have high zero shear rate melt viscosity that avoids the need for adding gels, so as to obtain stable and clear parison. Further, the PET is desired to have low rate of crystallization with lower crystallinity so as to be easy to process at lower temperature.
The present disclosure provides a process for the preparation of polyethylene terephthalate (PET). The process is simple and economical yielding PET having increased intrinsic viscosity, higher melt strength thereby making it processable in extrusion blow molding (EBM) even at lower processing temperature.
In an aspect, the present disclosure provides a process for preparation of polyethylene terephthalate. The process comprises esterifying terephthalic acid by reacting with monoethylene glycol, to obtain an esterified mixture.
The molar ratio of the terephthalic acid to the monoethylene glycol is in the range of 1:1 to 1:5. In an embodiment, the molar ratio of the terephthalic acid to the monoethylene glycol is 1:2.
In an embodiment, the terephthalic acid is purified terephthalic acid. The purified terephthalic acid has a purity of at least 99%.
In an embodiment, the step of esterification comprises mixing terephthalic acid and monoethylene glycol with an alkali metal hydroxide, under stirring, to obtain slurry. The slurry is heated at a temperature in the range of 200 oC to 270 oC, for a time period of 3 hours to 5 hours, at a pressure in the range of 1 bar to 3 bar, to obtain the esterified mixture.
In an exemplary embodiment, the slurry is heated for 3.5 hours at 260 oC at a pressure of 2 bar, in an esterification reactor, to obtain the esterified mixture.
The alkali metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. In an exemplary embodiment, the alkali metal hydroxide is sodium hydroxide.
The alkali metal hydroxide acts as Diethylene glycol (DEG) suppressant. DEG is formed during the step of esterification of the terephthalic acid with the monoethylene glycol. The incorporation of diethylene glycol moieties in the polyester reduces the melting point, reduces the glass transition temperature and crystallization level. The content of diethylene glycol residues in the polyester is reduced by the addition of the alkali metal hydroxide.
In an embodiment, a co-monomer is added in the step of esterification.
The co-monomer is at least one selected from isophthalic acid (IPA) and 2-methyl-1,3-propanediol. The absence of comonomer leads to faster crystallization making it difficult to blow mold.
In one exemplary embodiment, isophthalic acid (IPA) is added as the co-monomer in the step of esterification. The use of IPA as a co-monomer causes reduction in the crystallization of PET and improvement in transparency.
In another exemplary embodiment, both isophthalic acid (IPA) and 2-methyl-1,3-propanediol are added as co-monomers. The combination of IPA and 2-methyl-1,3-propanediol has a synergic effect on crystallization that helps to retain melt strength at higher temperature. The combination of co-monomers, IPA and 2-methyl-1,3-propanediol, thus provides relatively broad processing temperature range, unlike conventional PET.
The amount of the isophthalic acid is in the range of 1 wt% to 10 wt% with respect to the terephthalic acid. In an embodiment, the amount of isophthalic acid is 2.2 wt% with respect to the terephthalic acid.
The amount of 2-methyl-1,3-propanediol is in the range of 2 wt.% to 5 wt.% with respect to terephthalic acid. In one exemplary embodiment, the amount of 2-methyl-1,3-propanediol is 2.9 wt.% with respect to terephthalic acid. In another exemplary embodiment, the amount of 2-methyl-1,3-propanediol is 4.7 wt.% with respect to terephthalic acid.
In one exemplary embodiment, a mixture of purified terephthalic acid, isophthalic acid and monoethylene glycol (MEG), is subjected to esterification in an esterification reactor for 3.5 hours at 260° C under a nitrogen pressure of 2 bar to obtain an esterified mixture.
In the next step, the esterified mixture is pre-polymerized by adding a catalyst, a thermal stabilizer and a branching reagent to obtain a pre-polymer.
The catalyst is at least one selected from antimony oxide and stannous oxalate. In an embodiment, the catalyst is a mixture of antimony trioxide and stannous oxalate.
The amount of antimony trioxide is in the range of 150 ppm to 300 ppm as antimony metal. In an exemplary embodiment, the amount of antimony trioxide is 290 ppm based on antimony metal with respect to the terephthalic acid.
The amount of stannous oxalate is in the range of 15 ppm to 80 ppm as compound. In an exemplary embodiment, the amount of stannous oxalate is 70 ppm.
The thermal stabilizer is a phosphate compound selected from the group consisting of lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogenphosphate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogenphosphate, potassium phosphate, potassium dihydrogen phosphate, dipotassium hydrogenphosphate, strontium phosphate, strontium dihydrogen phosphate, distrontium hydrogenphosphate, zirconium phosphate, barium phosphate, aluminum phosphate, phosphoric acid and zinc phosphate.
In an embodiment, the thermal stabilizer is orthophosphoric acid.
The thermal stabilizer is mainly a source of phosphorous, and is added to decrease the thermal degradation of the polymer.
The amount of phosphorous in the thermal stabilizer is in the range of 5 ppm to 35 ppm. In one exemplary embodiment, the amount of phosphorous in the thermal stabilizer is 25 ppm.
The branching agent is selected from the group consisting of pentaerythritol (C(CH2OH)4), trimesic acid (C6H3(COOH)3), pyromellitic acid (C6H2(COOH)4), pyromellitic dianhydride, trimellitic acid, trimellitic anhydride, and trimethylol propane (C2H5C(CH2OH)3).
The addition of branching agent improves melt viscosity and melt strength. In an embodiment, the branching agent is pentaerythritol.
The branching agent is added in an amount in the range of 400 ppm to 750 ppm . In an embodiment, the branching agent is added in an amount of 500 ppm.
The step of pre-polymerization is carried out at a temperature in the range of 250°C to 265°C for a time period in the range of 3 hours to 4.5 hours. In an exemplary embodiment, the step of pre-polymerization is carried out at 260°C for a time period of 4 hours.
In an embodiment, at least one of the catalyst, the thermal stabilizer or the branching agent, are diluted with one or more glycol compound, prior to adding into the esterified mixture. In an exemplary embodiment, the glycol compound is monoethylene glycol.
In an exemplary embodiment, the esterified mixture is pre-polymerized by adding antimony trioxide and stannous oxalate to the esterified mixture, followed by the addition of pentaerythritol and 2-methyl-1,3-propanediol to obtain a mixture. The mixture is stirred for 5 minutes followed by the addition of orthophosphoric acid and further stirred for 5 minutes to obtain the pre-polymer.
Further, the pre-polymer is polymerized at a temperature in the range of 270 oC to 300 oC, for a time period in the range of 80 minutes to 150 minutes, to obtain a polymeric product comprising polyethylene terephthalate having intrinsic viscosity of less than 0.65 dL/g.
In accordance with an embodiment of the present disclosure, during the step of polymerization, the pressure is slowly reduced to 1mmHg.
In an embodiment, the polymerization technique is melt polymerization.
In accordance with the present disclosure, a blue toner and a red toner, are added to the pre-polymer, prior to polymerization.
The blue toner assists in masking yellowness of the polymer formed and red toner helps in masking the greenish tinge which could be due to higher loading of the blue toner.
In an exemplary embodiment, the pre-polymer is polymerized at 290 °C, for a time period of around 120 minutes, to obtain a polymeric product comprising polyethylene terephthalate having intrinsic viscosity of 0.625 dL/g.
The polymeric product is poly-condensed by solid state polymerization at a temperature in the range of 190 oC to 230 oC, for a time period in the range of 8 hours to 24 hours, to obtain polyethylene terephthalate having an increased intrinsic viscosity in the range of 0.85 dL/g to 1.2 dL/g.
In accordance with the present disclosure, the polymeric product is crystallized, prior to the solid-state polymerization.
In an embodiment, the polymeric product is taken in the form of chips.
In an exemplary embodiment, the chips of the polymeric product are crystallized at 140° C in an oven, prior to the step of solid state polymerization at 217° C for 16 hours to obtain the polyethylene terephthalate resin having an intrinsic viscosity in the range of 0.85 dL/g to 1.2 dL/g.
In another aspect, the present disclosure provides a polyethylene terephthalate resin characterized by having an intrinsic viscosity in the range of 0.85 dL/g to 1.2 dL/g and crystallinity in the range of 35% to 55%.
In an embodiment, the present disclosure provides a polyethylene terephthalate resin having an intrinsic viscosity of 1.117 dL/g and crystallinity of 46.9%.
In accordance with the present disclosure, the polyethylene terephthalate obtained by the process of the present disclosure, has relatively better processability for extrusion blow molding.
In accordance with the present disclosure, the polyethylene terephthalate resin is blow molded to obtain a blow molded article.
In an embodiment, the polyethylene terephthalate resin characterized by having an intrinsic viscosity in the range of 0.85 dL/g to 1.2 dL/g and crystallinity in the range of 35% to 55%, is extruded using a single screw extruder having an attached blow molding equipment, to obtain a blow molded article.
The extruder blow molding processing temperatures is in the range of 220° C to 255 °C. The parison obtained from the die is blown using a mold to obtain the blow molded article. In one embodiment, the blow molded article is a bottle having holding capacity of 500 ml liquid. In another embodiment, the blow molded article is a bottle having holding capacity of 4000 ml liquid.
In an embodiment, prior to extrusion blow molding, the polyethylene terephthalate is dried at a temperature in the range of 150 ° C to 180 ° C for a time period in the range of 4 to 6 hours.
In an exemplary embodiment, the polyethylene terephthalate is dried at 170° C for 5 hours, prior to extrusion blow molding.
The better processability of the polyethylene terephthalate of the present disclosure makes it easy and convenient to form containers having complex shapes such as container with handle, thick bottom containers and the like.
The present disclosure provides polyethylene terephthalate having relatively increased intrinsic viscosity, high melt strength, lower processing temperatures, slower rate of crystallization and good clarity. The polyethylene terephthalate has better processability in extrusion blow molding.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following laboratory scale experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
EXPERIMENTAL DETAILS:
Example 1: Preparation of PET (Sample 1):
Purified terephthalic acid (46.2 kg) was esterified with monoethylene glycol (MEG) (35.3 kg) in an esterification reactor for 3.5 hours at 260° C under a nitrogen pressure of 2 bar to obtain an esterified mixture. A co-monomer i.e. isophthalic acid and sodium hydroxide (25ppm) as DEG suppressant was also added in the esterification reactor. The esterified mixture was pre-polymerized at 260°C for a time period of 4 hours by adding catalyst [mixture of antimony trioxide (19 g) and of stannous oxalate (70 ppm) in 250 ml monoethylene glycol], branching agent [0.05 wt% of pentaerythritol dissolved in 100 g monoethylene glycol] and a thermal stabilizer [10 ppm (as P) orthophosphoric acid in 50 ml of monoethylene glycol], wherein each of the addition was done within a time interval of 5 minutes under stirring, to obtain a pre-polymer.
2.9 wt% of co-monomer i.e. 2-methyl-1,3-propanediol was also added to the esterified mixture, along with the addition of pentaerythritol. A blue toner and a red toner were added to the pre-polymer. After an interval of 10 min, the resultant mixture was transferred to a polymerization reactor wherein the polymerization was carried out at 290° C, while the pressure was gradually reduced to 1 mmHg to obtain a polymeric product. The intrinsic viscosity of the polymeric product was found to be 0.62 dL/g using ASTM D4603 test procedure. Chips of the polymeric product were crystallized at 140° C in an oven, and then subjected to solid state polymerization at 217° C for 16 hours to obtain the polyethylene terephthalate copolymer resin having an intrinsic viscosity of greater than 1 dL/g (as mentioned in Table 5).
Example 2: Preparation of PET (Sample 2):
The procedure as given in Example 1 was repeated, except that isophthalic acid was not added and the concentration of 2-methyl-1,3-propanediol was increased to 4.7 wt%.
Example 3: Preparation of PET (Sample 3):
The procedure as given in Example 1 was repeated, except that 2-methyl-1,3-propanediol was not added and the concentration of isophthalic acid was increased to 6.5 wt% and the concentration of the thermal stabilizer was increased to 30 ppm, instead of 10 ppm.
Comparative example 1: Preparation of reference PET sample (Sample A):
The procedure as given in Example 1 was repeated, except that isophthalic acid was not added and the concentration of 2-methyl-1,3-propanediol increased to 5 wt%, and the pentaerythritol was added in concentration of 500 ppm along with 1 wt.% of steric acid.
Comparative example 2: Preparation of reference PET sample (Sample B):
A control sample B was also prepared by adding the reactants in an amount as given in Table 1. The procedure as given in Example 1 was repeated, except that 2-methyl-1,3-propanediol and pentaerythritol were not added.
The details of the amount of reactants/reagents used in the above mentioned Examples 1-3 and the comparative examples 1 and 2 are summarized in Table 1.

Table 1: Quantities of the amount of reactants/reagents used
Components Amount (units) Example 1 Example 2 Example 3 Comp Ex
1 Comp Ex
2
PET Sample obtained Sample 1 Sample 2 Sample 3 Reference Sample A Control compound B
Mole ratio of terephthalic acid and monoethylene glycol - 1 : 2 1 : 2 1 : 2 1 : 2 1:2
Sb2O3 ppm as Sb 290 290 290 290 290
NaOH ppm NaOH 25 25 25 25 25
Phosphoric acid ppm as P 25 25 30 30 25
Isophthalic acid (IPA) wt.% 2.2 - 6.5 - 1.8
Stannous Oxalate ppm as compound 70 70 70 70 70
pentaerythritol ppm 500 500 500 550 -
2-methyl-1,3-propanediol wt.% 2.9 4.7 - 5 -
Blue toner ppm 7 7 7 15.0 7
Red toner ppm 2 2 2 5.0 2

Processing parameters in the step of esterification and polymerization:
The processing parameters (temperature and time) in the step of esterification and polymerization with respect to Examples 1-3 and the comparative examples 1 and 2 are summarized in Table 2 and the characteristics of the polyethylene terephthalate obtained after polymerization (prior to solid state-polymerization) is as summarized in Table 3.
Table 2: Processing parameters (temperature and time) for esterification and polymerization
Processing temperature Units Example 1 Example 2 Example 3 Comp Ex 1 Comp
Ex 2
Esterification Time min 216 225 194 240 216
Esterification temperature °C 262 262 262 260 262
Polymerization time min 123 113 91 187 107
Polymerization temperature °C 290 290 290 290 290

Table 3: Properties of PET obtained after polymerization step (prior to SSP step)
Property/PET obtained prior to SSP step Units PET from Example 1 PET from Example 2 PET from Example 3 PET from Comp Ex 1 PET from Comp
Ex 2
Intrinsic viscosity (IV) dL/g 0.625 0.614 0.634 0.610 0.635
Lightness value (L*) Hunter 72.2 72.9 72.15 63.8 70.5
Yellowness index
measured by CIA method (a*) Hunter -0.74 -1.6 -1.08 -1.8 -1.02
Yellowness index measured by CIA method (b*) Hunter -0.21 0.02 0.2 15.8 -0.01
Acid value meq/kg 24 21 24 32 25
Chips/g 87 88 85 82 88

As observed in Table 2, the reaction time of polymerization was relatively lesser (91 mins) in Example 3, due to the relatively higher amount of co-monomer addition i.e. 6.5 wt.% of Isophthalic acid. The PET obtained from comparative example 1 (before SSP) has relatively higher polymerization time.
The polymerization time for Examples 2 and 3, were relatively lesser than the comparative example 1 (sample A) which required longest time for polymerization. The reduction in polymerization time is economically advantageous.
Further, as observed in Table 3, the intrinsic viscosity and the optical properties of the samples as per the present disclosure (PET Samples from examples 1-3) are comparable to that of the reference sample B. The PET sample from comparative example 1 has relatively lesser lightness value and b* value, due to relatively higher loading of aliphatic co-monomer (i.e. 2-methyl-1,3-propanediol) that also leads to reduction in melt viscosity, and subsequent increase in the thermal degradation.
Processing parameters in the step of polycondensation:
The processing time in the step of solid state polymerization and the resulting change in intrinsic viscosity for Examples 1-3 and the comparative examples 1 and 2 are as summarized in Table 4 and also in Figure 1, whereas the corresponding properties of the polyethylene terephthalate obtained from solid state-polymerization is summarized in Table 5.
In the step of solid state polymerization (SSP), the chips (crystallized as provided in Example 1) were added in SSP batch reactor and the initial gas temperature was maintained at 180°C for 1 hour, and further kept at 212°C for 1 hour. The final gas temperature was kept at 217°C till the desired intrinsic viscosity (IV) was obtained. The chip temperature was around 208°C.
Table 4: Processing time and intrinsic viscosity (IV) in solid state polymerization
Reaction time (in hrs) Example 1 Example 2 Example 3 Comp Ex
1 Comp Ex
2
0 0.625 0.614 0.634 0.610 0.635
2 0.705
4 0.789 0.745 0.798 0.639 0.736
6 0.803
8 0.88 0.827 0.923 0.81 0.855
12 0.928 0.938 0.86
15 1.038 0.981
16 1.02 1.115 0.883
17 1.117 1.046
18 1.192 0.928
24 1.034
*IV/hr 0.0319 0.0266 0.0361 0.0250 0.0275
* IV rise is considered for 8hrs to compare with Control sample B
As observed in Table 4, the reactivity was relatively better for Example 3 (higher rate of change in intrinsic viscosity with time, due to the relatively higher amount of co-monomer addition i.e. 6.5 wt.% of Isophthalic acid. Further, the desired intrinsic viscosity (IV) (greater than 1 dL/g) was obtained for Examples 1 and 2 in less than 18 hours, whereas for comparative example 1, the SSP time was relatively greater than other examples. This indicates improvement in productivity of the process of the present disclosure. Example 1 employing a combination of both co-monomers, had an improved reactivity in SSP, however, example 1 exhibited relatively lesser reactivity than example 3 that uses higher quantity of isophthalic acid.
Table 5: Property characteristics of PET obtained after SSP
Property Unit Sample 1 Sample 2 Sample 3 Reference Sample A Control compound B
IV dL/g 1.117 1.046 1.192 1.034 0.855
L* Hunter 85.11 85.73 85.3 80.1 86.0
a* -1.43 -1.81 -1.5 -2.2 -1.4
b* 0.024 -0.12 1.4 13.3 -0.5
-COOH meq/kg 12 9 10 - -
Density g/cm3 1.3912 1.3914 1.4014 1.3871
% crystallinity % 46.9 47 55.3 43.5

As observed in Table 5, the color values of all batches are comparable except for reference sample A, which has relatively lower L value and relatively higher b color (increase in yellowness). The poor color properties of the reference sample A could be attributed to the presence of chain termination agent i.e. stearic acid.
The density and crystallinity for sample 1 having combination of both the co-monomers (IPA and 2-methyl-1,3-propanediol) was much lower as compared to other samples 2-3 and reference sample B. However, the crystallinity was lowest with the old recipe probably due to the higher addition of 2-methyl-1,3-propanediol and chain terminating agent.
Thermal analysis of the samples
Thermal analysis was carried out for samples 1-3 and reference sample A and reference sample B (control compound). The thermal analysis was done using Perkin Elmer diamond DSC. The results are as summarized in Table 6. The thermal analysis graph for sample 1, is illustrated in Figure 2.
Table 6: Thermal analysis
1st Heating run Sample 1 Sample 2 Sample 3 Reference Sample A Control compound B
Melting Tg. °C 72.32 70.98 72.21 70.53
Onset °C 222.44 224.27 226.11 224.33 233.36
2nd Peak 230.83 233.81 234.68 233.26 248.37
End temp. °C 239.97 242.16 243.62 241.86 255.67
? Hm J/g 53.98 54.1 54.74 53.23 61.06
Cooling run
Crystallization Onset temp. °C 181.29 205.47 210.99 204.6 208.57
Peak °C 159.78 199.37/ 169.63 205.84/ 178.26 197.34 192.5
End temp. °C 139.41 148.24 166.11 181.22 179.72
?Hc J/g -12.59 -16.34 -24.37 -6.19 -31.73
2nd Heating
Melting
Onset temp. °C 216.24 223.9 224.62 214.46 232.67
Peak °C 234.68 238.52 238.07 234.06 247.74
End temp. °C 244.72 249.1 248.74 242.59 256.77
? Hm J/g 33.31 36.53 22.07 32.26 37.09

As observed in Table 6, the melting point in the first heating for sample 1 having combination of comonomer was lower than all other samples. The sample 1 has broader crystallization temperature wherein the crystallization peak is lower than other batches. It also suggests that combination of comonomers creates slow crystallization.
Melt rheology of samples
Melt rheology of the PET samples were carried out to understand the flow behavior and viscosity of the samples, at elevated temperature. It is known that higher melt viscosity is related to higher flow resistance. The pre-dried samples were analyzed at 260°C and 280°C with L/D being 10:1 at different shear rates ranging from 100 to 10000 sec-1 as provided in Table 7. The graphical representation of the change in melt viscosity for the samples with respect to shear rate at 260°C and 280°C is as shown in Figures 3(A) and 3(B) respectively.
Table 7: Melt rheology
260 °C 280 °C 280 °C
Shear rate Sample 1 Sample 2 Sample 3 Reference Sample A Control compound B Sample 1 Sample 2 Sample 3 Reference Sample A
100 872 964 1403 860 372 756 451 1104 262
250 727 693 915 656 249 615 400 778 275
500 582 570 687 466 285 506 352 604 231
1000 432 417 517 352 266 385 290 452 213
2500 300 277 332 244 188 235 191 290 177
5000 219 210 272 207 126 167 134 214 129
7500 164 159 177 184 96 122 103 169 109
10000 136 132 - 151 77 106 80 140 98

As observed in Table 6 and Figures 3(A) and 3(B), the samples 1-3 has higher melt viscosity when measured at 260°C. However, small changes in melt viscosity were observed when tested at 280°C. This trend was valid for both high isophthalic acid (IPA) and mixed co-monomer based PET. Further, the melt viscosities of all samples (samples 1-3) were higher than reference sample A. at 260°C. This could be due to the presence of chain terminating agent in sample A, which acts as internal lubricant or processing aid. It was also observed that the viscosity of batch containing higher loading of IPA (sample 3) was higher than other samples (1 or 2), especially at 280°C. The melt viscosity also decreased with increase in the content of 2-methyl-1,3-propanediol. These studies suggest that the melt viscosity of reference sample A is highly sensitive to processing temperature, whereas the samples 1 to 3 have relatively broader processing window.
Product performance evaluation:
The so obtained polyethylene terephthalate samples (samples (1-3) were dried at 170° C for 5 hours and extruded using a single screw extruder having an attached blow molding equipment. The extruder screw L/D ratio was 24 and processing temperatures were kept between 220° C and 245° C. The parison obtained from the die was blown using a mold to obtain a blow molded product. The blow molded product obtained from PET samples 1 and 3, are as shown in Figures 4(A) and 4(B) respectively.
It was observed that, by using the PET samples 1 and 3 of the present disclosure, it was possible to blow mold the samples upto 5 litre capacity to obtain container with handle, whereas with the reference PET sample A, it was possible to blow mold only upto 500 mL. The blow molded articles had relatively better clarity than containers obtained from conventional PET.
The present disclosure provides a simple and economical process that gives polyethylene terephthalate having comparatively better processability in extrusion blow molding, relatively high melt strength, lower processing temperatures, slower rate of crystallization. The blow molded articles obtained from the PET samples, prepared by the process of the present disclosure, have relatively higher capacity and better clarity than conventional PET samples.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing PET that:
• is simple and economical;
• provides polyethylene terephthalate having comparatively better processability in extrusion blow molding;
• provides polyethylene terephthalate having relatively high melt strength, lower processing temperatures, and slower rate of crystallization; and
• provides PET for obtaining blow molded product having relatively higher capacity and better clarity than conventional PET samples.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. ,CLAIMS:WE CLAIM:
1. A process for preparing polyethylene terephthalate, said process comprising the following steps:
a. esterifying terephthalic acid by reacting with monoethylene glycol, to obtain an esterified mixture;
b. pre-polymerizing said esterified mixture by adding a catalyst, a thermal stabilizer and a branching reagent to obtain a pre-polymer;
c. polymerizing said pre-polymer at a temperature in the range of 270 oC to 300 oC, for a time period in the range of 80 minutes to 150 minutes, to obtain a polymeric product comprising polyethylene terephthalate having an intrinsic viscosity of less than 0.65 dL/g; and
d. polycondensing the polymeric product by solid state polymerization at a temperature in the range of 190 oC to 230 oC, for a time period in the range of 8 hours to 24 hours, to obtain polyethylene terephthalate having an increased intrinsic viscosity in the range of 0.85 dL/g to 1.2 dL/g.
2. The process as claimed in claim 1, wherein the terephthalic acid is purified terephthalic acid.
3. The process as claimed in claim 1, wherein said step of esterification comprises the following steps:
(a) mixing terephthalic acid and monoethylene glycol with an alkali metal hydroxide, under stirring, to obtain a slurry; and
(b) heating said slurry at a temperature in the range of 200 oC to 270 oC for a time period in the range of 3 hours to 5 hours, at a pressure in the range of 1 bar to 3 bar, to obtain the esterified mixture.
4. The process as claimed in claim 3, wherein said alkali metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide.
5. The process as claimed in claim 1, wherein the molar ratio of said terephthalic acid to said monoethylene glycol is in the range of 1:1 to 1:5.
6. The process as claimed in any of the preceding claims, wherein the molar ratio of said terephthalic acid to said monoethylene glycol is 1:2.
7. The process as claimed in claim 1, wherein at least one co-monomer is added in at least one step selected from esterification and pre-polymerization.
8. The process as claimed in claim 7, wherein said co-monomer is at least one selected from isophthalic acid and 2-methyl-1,3-propanediol.
9. The process as claimed in claim 8, wherein the amount of said isophthalic acid is in the range of 1 wt% to 10 wt% with respect to said terephthalic acid, or wherein the amount of 2-methyl-1,3-propanediol is in the range of 2 wt.% to 5 wt.% with respect to said terephthalic acid.
10. The process as claimed in claim 1, wherein said catalyst is at least one selected from antimony oxide and stannous oxalate, wherein the amount of antimony trioxide is in the range of 150 ppm to 300 ppm as antimony metal, or wherein the amount of stannous oxalate is in the range of 15 ppm to 80 ppm.
11. The process as claimed in claim 1, wherein said thermal stabilizer is a phosphate compound selected from the group consisting of lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogenphosphate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, strontium phosphate, strontium dihydrogen phosphate, distrontium hydrogen phosphate, zirconium phosphate, barium phosphate, aluminum phosphate, phosphoric acid and zinc phosphate.
12. The process as claimed in claims 1 or 11, wherein said thermal stabilizer is orthophosphoric acid.
13. The process as claimed in claim 1, wherein said branching agent is selected from the group consisting of pentaerythritol (C(CH2OH)4), trimesic acid (C6H3(COOH)3), pyromellitic acid (C6H2(COOH)4), pyromellitic dianhydride, trimellitic acid, trimellitic anhydride, and trimethylol propane (C2H5C(CH2OH)3), or wherein said branching agent is added in an amount in the range of 400 ppm to 750 ppm.
14. The process as claimed in claim 1 or claim 13, wherein said branching agent is pentaerythritol.
15. The process as claimed in claim 1, wherein a blue toner and a red toner are added to the pre-polymer, prior to polymerization.
16. The process as claimed in claim 1, wherein said pre-polymerization is carried out at a temperature in the range of 250°C to 265°C for a time period in the range of 3 hours to 4 hours.
17. The process as claimed in claim 1, wherein said polymerization is melt polymerization.
18. The process as claimed in claim 1, wherein the polymeric product is crystallized, prior to solid-state polymerization.
19. A polyethylene terephthalate resin characterized by having an intrinsic viscosity in the range of 0.85 dL/g to 1.2 dL/g and crystallinity in the range of 35% to 55%.
20. The polyethylene terephthalate resin as claimed in claim 19, wherein the resin is blow molded to obtain a blow molded article.