Indian Journal of Fibre & Textile Research Vol. 16, March 1991, pp. 12-24

Utilization of polyester waste generated in fib're production plants

B N Baodyopadhyay, N Pawar, P C Meh~a & S N Huddar The Bombay Textile Research Association, L B S Marg, Ghatkopar (West), Bombay 400 086, India

Received 14 November 1990

Various types of polyester waste were collected from different polyester fibre manufacturing plants. Using various reagents, the polyester wastes were converted into alkyd and polyurethane resins and also into other useful products. The methods of conversion are discussed and the properties and applications of the products so prepared are described .

Keywords: Alkyds, Glycolysis, Polyester waste, Polyurethanes

I Introduction Synthetic fibres account for about 36% of the total

textile fibre production in the world l ao Amongst the synthetic fibres, the production and growth of polyester fibres is the highest. The world production of poly(ethylene terephthalate) (PET) fibres increased I b from 5053 thousand tons in 1980 to 8122 thousand tons in 1988. During the same period the production of polyamide fibres rose from 3185 thousand tons to 3704 thousand to'ns and that of acrylic fibres from 2024 tons to 2514 thousand tons. In India also, the production of PET filament and staple is the highest amongst the synthetic fibres; it rose from \08 thousand tons in 1985 to an estimated value of280 thousand tons tn 1990. During the production of PET filament and staple, certain amounts of wastes are generated at various stages of production. The extent of waste generation depends on a number of factors . It may arise as a result of deviation in production parameters, fault of operators or machines or due to the use of sub-standard raw material. Technological insufficiency may also contribute to inferior quality of fibres being produced which also form waste. Apart from these, soiled or contaminated chips or fibres are also generated due to equipment breakdown, power failure or other operational problems in the industry. The present work represents an attempt to convert the waste into alkyds and urethanes for use in textile applications.

2 The Amount and Types of Waste The extent of waste generation during the

production of polyester is' generally around 7% of the total production 1 out of which 4% is reused by the industry for converting it back into raw materials.

12

The remaining 3% waste is difficult to reutilize easily. This non-biodegradable waste is either sold at a throwaway price or is dumped in the backyard of the factory premises.

The polyester waste generated in a plant is generally classified as belonging to one of the following three" categori!!s:

(i) Soft Waste: Mainly drawn or undrawn tow or staple, low-oriented yarn (LOY), partially-oriented yarn (POY) and textured or twisted yarn waste.

(ii) Hard Waste : Lump polymers, spin head/extruder solid wastes, polymer rods or tapes, etc.

(iii) Contaminated Waste; Coloured chips or fibrous waste (pigmented or thermally degraded), floor sweepings, etc.

In the industry, both soft and hard wastes are reused by converting them back either to terephthalic acid or dimethyl terephthalate or into polymer granules2 - 6. Various technologies are available for these conversions. These recycled granules or monomers are blended to the extent of 5-20% with the fresh raw material.

3 Methods of Recovery For the recovery of the waste ,as powder or

granules, solvent precipitation or mechanical methods are employed.

For conversion into polyester powder, the waste polymer is dissolved in solvents such as naphthalene, biphenyl ether, phenanthracene, etc. at temperatures ranging between 180°C and 240°C. These solvents do not depolymerize the polyester. Water is used as a non-solvent for precipitating the dissolved polyester 7.8.

BANDYOPADHYAY et at.: UTIliZATION OF POLYESTER WASTE

Forconverting into granules, the fibre waste iscut to a standard size followed by melting, degassing and homogenising. Then the filtered, molten polymer is either cast as a film or a tape which may be granulated with the help of a standard dicer or granulator.

Recovery as monomers can be achieved by different techniques. The depolymeriza tion of the polyester waste materials is generally done by glycolysis, hydroly"sis or methanolysis. These processes are briefly described below.

3.1 Glycolysis

In glycolysis, polyester waste material is boiled with monoethylene glycol with or without catalyst at different temperatures for different durations to produce diglycol terephthalate9 - II (DGT). The diglycol ester ofterephthalic acid is at times purified and mixed with freshly prepared prepolymers for polycondensation. S-2S% of recycled diglycol terephthalate is used. Purification of DGT by distillation is not practicable as it polymerizes and, therefore, good quality waste material is taken for glycolysis. Dimethyl terephthalate (DMT) is also recovered from the polyester waste by glycolysis. Waste material is boiled with monoethylene glycol up to the completion of reaction to obtain DGT. The excess glycol is removed by vacuum distillation and heated in methanol at the boil. DMT crystals separated from the solution are purified by solvent washing and vacuum distillation.

3.2 Hydrolysis

Polyester waste can also b(l hydrolyzed with alkali, acid and water. In alkali hydrolysis 12, strong caustic soda solution (12-20%) is used to saponify the polyester at ISO-ISO·C. Hydrochloric acid is added to precipitate terephthalic acid, which is further purified. Various amines such as cyclohexylamine and piperidine, etc. are used as additives. For the acid hydrolysis, strong inorganic acids such as 7S% sulphuric acid, 70% phosphoric acid and SO% nitric acid are used l3 . Terephthalic acid is purified through it's sodium salt and DMT is produced after esterification with methanol. The dimethyl ester of terephthalic acid is purified for further use.

Hydrolysis of polyester waste can also be done in steam in a pressure vessel at high temperature and high pressure. Pure terephthalic acid can be obtained by this method l4 . Hydrolysis can also be catalyzed with sodium acetate, zinc acetate l5 or calcium acetate. Terephthalic acid and ethylene glycol can be continuously recovered l6 from polyester waste by hydrolysis in a neutral-aqueous medium at high temperature and pressure followed by

decolourization by charcoal. Terephthalic acid and ethylene glycol are recovered from mother liquor by continuous distillation .

3.3 Methanolysis

DMT can also be recovered by methanolysis. Polyester is treated with methyl alcohol vapour at high pressure with acid catalyst. Usually a temperature in the range lS0-20S·C is required to depolymerize. The pressure is varied from 20 to 34 kg/cm2 and the reaction is continued for 2-3 h. DMT is crystallized and purified by various methods. In this method, methyl hydroxyethyl terephthalate (MHET) is also produced along with monoethylene glycol. MHET can also be converted into DMT ,by refluxing with sodium carbonate for 2-3 h.

4 Scope of the Present Investigation In the present investigation, the efforts have been

predominantly directed towards the recovery of basic monomers from polyester fibre waste. However, attempts have also been made to develop other commercially useful products and auxiliaries such as films, adhesives, varnishes, plasticizers and polyurethanes I 7 - 23. Diglycol terephthalate obtained from the polymer waste was reacted with poly(ethylene oxybenzoate) in the presence of oligomeric polyesters to produce a polyester copolymer24. Polyester waste was recycled with magnesium silicate, calcium stearate, zinc stearate and/or aluminium silicate to produce speciality polymers for injection moulding25 . Attempts have been made to produce polyurethane foams by digesting polyester waste with glycols followed by the addition ofthiodiethylene glycol to produce polyols which can be used for the preparation of rigid polyurethane foams 26 .

However, considering the importance of the problems related to the disposal of polyester waste and the feasibility of their conversion into textile auxiliaries, there is considerable scope for innovative and systematic research in this field. The cleanliness of the environment and the production of commercial products with techno-economical viability arc the two important consequences of such work. The present work involved the chemical treatment of polyester waste with the aim of converting it into alkyds and urethanes which can be used for textile applications.

5 Materials and Methods Various types of polyester waste were collected

from different polyester fibre manufacturers. They were used for the depolymerization/degradation

13

INDIAN 1. FIBRE TEXT. RES., MARCH 1991

work after proper identification. Two types of polyester wastes were mainly studied, viz. (i) hard waste obtained during spinning operations, e.g. spin head waste, lumps, fibre/solid extruder waste, etc. and (ii) soft waste obtained during spinning and post-spinning operations, e.g. drawn/undrawn waste, POY, LOY, grey textured/grey twist filament yarn waste, etc. These waste materials were screened for physical appearance, percentage of water-soluble matter, dioxane-soluble matter, etc.

The reagents used for the treatment of polyester waste were sulphuric acid, sodium hydroxide, methanol, various glycols (monoethylene glycol, propylene glycol and diethylene glycol) along with catalysts sodium aceta te and zinc acetate, etc. All these reagents were of LR grade.

For alkyd preparation, various monomers such as maleic anhydride/acid and phthalic acid/anhydride were used along with catalysts diammonium hydrogen phosphate and trisodium phosphate.

For the preparation of polyurethane resins, toluene-2,4-di-isocyanate was used as the monomer along with different chain extenders, viz. pyridine, ethylene diamine, glycerols, glycols, etc. All these chemicals were of LR grade.

For high pressure reaction, a parr reactor system with Inconel and a Hastelloy vessel was used. Degraded products and chemically modified products were analyzed by thermal (Mettler HE20 TG and DT A) and infrared (Perkin-Elmer and Hitachi 270 - 30 Data Processor) studies. Shimadzu LC 6A with CR 4 A TO and fraction collector were employed for HPLC and GPC studies.

5.1 Depolymerization of Polyester Waste

Extensive studies on the depolymerization of polyester waste were carried out using different methods, viz. steam cracking, acid hydrolysis, alkali hydrolysis and glycolysis. The degradation was carried out at atmospheric pressure as well as at high pressure using high-pressure parr reactor. Polyester solid and lump wastes were subjected to steam cracking under hi,gh pressure using different ratios of polyester waste to water at temperatures ranging between 240°C and 310°C and pressure ranging from 400 to 1400 psi. The duration of reaction was between I hand 5 h. The products obtained were separated and characterized by determining melting point and solubility. TGA, DTA and IR spectral studies were also carried out for characterization .

Acid and alkali hydrolysis of polyester waste was carried out using different concentrations of sulphuric acid and sodium hydroxide under different pressures for different time durations. The reaction

]4

products were separated on the basis of their solubility parameter.

Glycolysis of polyester waste was achieved using monoethylene glycol, diethylene glycol , propylene glycol and polyethylene glycol-400. The glycolysis was carried out with different concentrations of glycols at elevated temperature with or without catalyst. The water-soluble and insoluble solids were separated . Their purity, physical properties and spectral data were studied for characterization.

5.2 Preparation of Alkyd and Urethane Resins

Bis-(2-hydroxyethyl)terephthalate (BHET) with m.p. llO-112°C was obtained by chemical degradation of polyester waste and mixed terephthalates (melting range, I 60-2 10°C). It was converted into alkyd and urethane resins as follows . The BHET and other products obtained from glycolysis were reacted with monomers such as maleic anhydride and phthalic anhydride to get alkyds. Similarly, it was reacted with toluene-2,4-di-isocyanate (TDI) to get the urethanes. A series of alkyds and urethane resins was prepared using different reaction parameters.

The GPC studies of alkyds and' PU resins were carried out with Shim-pack HSG 50S Column. THF was used as a mobile phase. Refractive index detector (RID) was used. 1.0 mg/ml sample was injected and CR4A TD chromatopac with the software version 1.0 was used for the analysis. For the calculation of molecular weight , 'Q' factor was taken as 1.0; a. & Kappa values were 0.706 and 0.00016 respectively. The molecular size was calculated by the supplied software of M/s Shimadzu Corporation. This computer does not give the unit as it depends on specific column. The retention in size exclusion chromatography is determined strictly by molecular size and it depends on the pore size of the column.

6 Results and Discussion

6.1 Steam Cracking

Steam cracking of hard lump waste was carried out at high temperature and pressure. The depolymerized products were separated, purified and characterized. They are listed in Table I.

It was found that terephthalic acid could be obtained by steam cracking. In the absence of a catalyst, various other products (water soluble and insoluble) were also produced. Although the reaction pressure, duration and temperature of the reaction and the amount of water influence the yield of products, two types of products were obtained in all cases. Water-insoluble products were termed as mixed terephthalates (m.p. 160-21 O°C). GPC, HPLC

BANDYOPADHYAY etal.: UTIUZAllON OF POLYESTER WASTE

Table I- Steam cracking of polyester waste under pressure using parr reactor (without catalyst)

[Reactants : Hard waste and water]

M:L Temp. and Reaction Products ratio period of pressure obtained

reaction psi

1:5 300-310·C 1400 Hot water soluble I h product (~ 5%)

m.p. 185-186·C

Terephthalic acid (- 85%)

1:5 300-31O·C 1350 Terephthalic acid 2h (- 18%)

Mixed terephthalates (- 75%) m.p. 170-21O·C

1:0.5 260-280·C 600 Hot water soluble I h product (- 18%)

m.p. 185-18TC

Terephthalic acid (- 15%)

Mixed terephthalates m.p. 170-210·C

1:0.5 245-250·C 400 Hot water soluble product 5 h (- 14%)

m.p. 185-186·C

Terephthalic acid (- 55%)

Mixed terephthalates (- 20%) m.p. 170-210·C

and IR studies revealed that hot water-soluble product contained different types of oligomers comprised of diethylene glycol unit. Fig. I shows the thermogravimetric and DT A curves of mixed terephthalates while Fig. 2 shows the TG and DT A traces of terephthalic acid obtained by steam cracking.

When the steam cracking was carried out with zinc acetate as the catalyst, it resulted in the separation of terephthalic acid only, even at a low pressure. The studies also revealed that without a catalyst, high pressure of 1400 psi was required to obtain the terephthalic acid from the hard polymer lump. By controlling the pressure, temperature and the duration of reaction, it is possible to obtain various oligomers and mixed terephthalates for different end uses.

6.2 Alkali and Acid Hydrolysis

Hydrolysis of polyester waste with alkali and acid

0

10

20

30

40 !

'or ;! rTI ~ 60 ><

III 0 III

1 0 70 r ...J

:x: 80 ~ I> I!) .... W 90 1 ~

100 ,., z 0 0

150

55

TEMP,oe

Fig. 1- TG and DT A curves of mixed terephthalates

<fr for (V

0 0 2

10 10 -+-TGA

20 -OTA 20 2 -.- TEM P

30 30

-:. 40 ~O

Vl 50 (1) Pure TPA Vl (2) T PA Obtained 0 50 rTI ...J 60 from waste >< 1 0 j: 60 70 t .., ~ 70 80 I> ....

80 90 ! .100 2 90 rTI

Z 0

100 0

160

55 TEMP. ,oe

Fig. 2- TG and DT A traces of pure terephthalic acid and terephthalic acid obtained after steam cracking

15

INDIAN J. FIBRE TEXT. RES. , MARCH 1991

was carried out individually in the parr reactor under high pressure. It was found that alkali hydrolysis invariably produced terephthalic acid. Depending upon the reaction conditions, the yield of terephthalic acid, unhydrolyzed waste and mixed depolymerized products (mixed terephthalates)

varied . The study revealed that up to 85% terephthalic acid could be obtained from the polyester solid waste as shown in Table 2.

Table 3 shows the results of acid hydrolysis of polyester waste under pressure. It is observed that at high pressure and temperature the product gets

Table 2- Alkali hydrolysis of polyester waste in parr reactor

[Reaction period, 1 hI

Reacta nts

Ha rd waste: Sodium hydroxide (5% w/v)

Ha rd waste : Sodium hydroxide (10% w/v)

Hard waste: sod ium hyd roxide ( 10% w/v)

Ha rd waste: Sodium hydroxide (10% wjv)

Hard waste: Sodium hydroxide (20% w/v)

M :L ra ti o

1:4

1:4

1:4

1:4

1:10

Reaction temp.

·C

290-295

250-255

270-275

290-295

300-305

Reacti on pressure

psi

1100

580

840

1060

11 20

Products obtained

Terephthalic acid (30%) Unhydrolyzed waste (64%)

Terephthalic acid (70% ) Mixed terephthalates (5%) m.p. 220-230·C Unhydro lyzed waste (10%)

Terephthalic acid (80% ) Mixed te rephthalates (5%) m.p. 220-250"C

Terephthalic acid (82%)

Terephthalic acid (85%)

Table 3- Acid hydrolysis of polyester waste under pressure in parr reactor

Reactants

Hard waste : Sulphuric acid (70% w/w)

Hard waste : Sulphuric acid (8.5% w/w)

Ha rd waste: Sulphuric acid (1% w/w)

Hard waste: Sulphuric acid (0.25% w/w)

Hard waste : Sulphuric acid (0.25% w/w)

16

M :L ratio

1:4

1:10

1:6

1:4

1:4

Temp. and period of reaction

206-210·C Ih

300-3 15"C I h

300-310·C Ih

260-270"c Ih

250·C 2 h

Reaction pressure

psi

100

1320

1320

640

600

Products obtained

Charred product

C harred product

Terephtha lic acid (blackish), 72%

Hot water soluble product (- 10% ) m.p. ISO-IS5·C Terephthalic acid (- 40%) Unhydrolyzed residt'Je (- 30%)

Hot water soluble prod uct (- 9%) m. p. 185- 186·C Terephtha lic acid (- 75%) Mixed terephtha late (- 2% ) m.p. 210-2 15"C

BANDYOPADHY AY el al.: UTILIZATION OF POLYESTER WASTE

charred. Even if I % w/w sulphuric acid is taken, 72% terephthalic acid could be obtained, which also was blackish in colour. When a very low concentration of sulphuric acid was used, terephthalic acid and other products were also obtained. It appeared that there was hardly any difference in the product mix obtained as compared to steam cracking experiments without the use of acid.

6.3 Glycolysis

Glycolysis of various types of polyester waste with different glycols was carried out under different reaction conditions. Monoethylene glycol (MEG), di'ethylene glycol (DEG), propylene glycol (PG) and polyethylene glycol (PEG-400) were taken for the studies. The reac tions were carried out at atmospheric pressure and also at elevated pressure . The temperature and duration of reaction and the concentration of reactants were va ried. Generally, it was found that two types of products, viz. bis(2-hydro,(yethyl)terephthalate (BHET) (hot water-soluble crystalline white solid, m.p. 110°C) and mixed terephthalates (water-insoluble powder, m.p. 160-225°q coul8 be obtained. Fig. 3 shows the TG and DT A traces of BHET.

The studies also revealed that if MEG concentration is increased along with the duration of boiling, maximum yield ofBHETcould be obtained. Addition of zinc acetate (0.4% on the polymer weight) could hasten the glycolysis reaction .

Table 4 shows the results of glycolysis of polyester waste using MEG at atmospheric pressure without any catalyst. It is observed that the yield of BHET depends on the amount of MEG used. When the ratio of polyester waste to MEG was equal to uni ty, 60% of BHET was produced. It was also found that yield of BHET remains the same for the different types of waste, i.e. undrawn, drawn fibre wastes, lump and chip wastes. When mixed terephthalates were further taken for glycolysis it could produce BHET.

However, in this case the use of zi nc acetate catalyst was essential.

Table 5 shows the results of glycolysis of polyester waste with MEG under pressure. The reaction could not be carried out at a very high pressure. It was found that even in the reaction under pressure, the amount of glycol used could virtually control the yield of BHET.

Table 6 shows the results of glycolysis of polyester waste using other glycols like diethylene glycol and propylene glyeol. It was found that these glycols could produce some polymer mass which could only

0

10

20

30

;! 1,0 ~

~ 50 0 ...J

.... 60 J: (!)

W 70 ~

80

90

100

225

..... TGA

- OTA -6- TEMP

110°C 170

110

1,5

Fig. 3-TG and DT A curves of BHET

rT1 >< 0

T t> .....

! rT1 Z 0 0

Table 4-Giycdlysis of polyester waste with monoethylene glycol

[Reaction temp. , 260-280·C; reaction period. I h]

Sample Quantity of ethylene Water-soluble Water-insoluble solid No. glycol used (% by wt. solid(BHET) (mixed terephthalates)

of polyester waste) % Yield m.p.

% ·C

I IO 100 230-250 2 30 20 80 155-225 3 40 30 70 161)-200 4 50 45 55 160-205 5 100 60 40 160-200

17

INDIAN 1. FIBRE TEXT. RES., MARCH 1991

Table ~Iyco l ys i s of polyes ter waste in the press ure reactor using monoethylene glycol with zinc acetate (0.4% ) as catalyst

Quantity of glycol used (% by wI. of polyester waste)

10

10

50

50

Temp. and period of react ion

260-280T 90 min

300'C I h

245-255'C I h

~45-250°C

I h

Reaction Products obtained pressure

pSI

60 BH ET (negligible) Mixed terephtha la tes (100% ) m.p. 2I0-215T

145 BHET (negligible) Mixed terephtha lates (100% ) m.p. 185-210T

20 BHET (40% ) Mixed terephtha la tes (60%) m.p. 140-1 60T

40 BHET (40% ) Mixed terephtha la tes (60%) m.p. 140-1 60T

Table 6-Glycolysis of po lyes ter waste using diethylene glycol. propylene glycol and polyethylene gl ycol (PEG-400) with 0.4% zi nc ace tate as ca ta lyst

Sample No .

I 2 3 4 5 6 7 8

Quantity of glycol" used (% by wI. of

polyester waste)

10 ~O

30 40 10 20 30 30

[Reaction period. I hI

Reaction Melting/softening temp. temperature of the

T reaction product

260-~80 ~ 15-230 260-280 180-195 260.280 160-175 ~60-280 I ~0-140 240-260 ~05-nO

240-260 175-'195 ~40-~60 1~5-140

~40-~60 195-~ 1 5

"Propylene glycol for samples 1-4. diethylene glycol for samples 5-7 and PEG-400 for sample 8. Yield obtained is about 100% on the weight of polyester waste taken.

be characterized through melting point. The separation of products from each reaction residue was very difficult as it contained different types of oligomers and polymers. No BHET could be obtained from these reactions.

melting point ranges. The products obtained from glycolysis of polyester using other glyco ls were totally water insoluble. These solids, when heated in silicone oil bath, could not produce a transparent clear melt but formed a turbid solution in hot DMF. GPC studies showed that these were of low molecular weight as compared to the polyester waste.

An attempt was also made to separate mixed terephthalates obtained from glycolysis reaction with- MEG. Low molecular weight products were obtained. IR studies showed that all of these products contained - CH~ - 0 - CO - linkage . The melting point of these compounds varied but was much lower than, the melting point of the polyester. Mixed terephth a lates obtained from steam cracking. acid hydrolysis and a lk a li hydro lysis showed different

I ~

6.4 Preparation of Alkyds and Urethanes

Alkyds and polyurethanes are an important class of resins which are used extensively as adhesives and coating materials. Alkyd resin is a type of polyester resin, made by the union of polyhydric alcohols and dibasic anhydrides/acids . Glycerol is the common

BANDYOPADHYAY el at.: UTILIZATION OF POLYESTER WASTE

alcohol and phthalic acid, the common acid used for the preparation of a lkyds. When a part of phthalic anhydride is replaced by oleic acid or maleic anhydride , the products obtained are more flexible and have better solubility properties than glycerol phthalate. By suitable variations, alkyds have been made by blending with a large number of other resins and polymers, to provide an almost endless array of important products for coating and allied industries.

The reaction of an isocyanate with an active hydrogen of a hydroxyl group such as polyester/polyether/polycarbonate/polyol results in the formation of urethanes. Aliphatic urethanes are more costly but they have superior light stability and low glass transition. Polyester diols , when used with isocyanate, form resins with higher degree of

00 0 II II

HO - CHI - CHI - a - C \ j C - 0 - CH I - CHI - OH +

SH ET

a " CH - C

I I '0 CH - c'

" a Ma leic Anhydr ide-

H f oac -CH = CH - COO - CHI - CHI - OOC 0 COO - CHI - CHI - at H

(n ~ I ~)

Alkyd

Fig. 4- Chemical structure of alk yd with ma leic a nhydride

flexibility and superior adhesion. Because the polyester segment is highly polar, adhesion to low energy surfaces is good . Urethane-based adhesives are currently being used by a variety of industries, including those producing fabrics and thin film packaging laminations for various functional end uses .

Some attempts which were made to develop various alkyds and urethanes out ofBHET and mixed terephthalates obtained from polyesfer wastes will now be briefly described .

BHET, when reacted With maleic anhydride, produced alkyd resins. Fig. 4 shows the possible .:hemical structure of the alkyd. The alkyd resins obtained by heating at atmospheric pressure were mostly sticky, yellowish brown solid, which softened between 70°C and 100°C and melted between 100°C and 140°C. The melt was turbid . The resins were insoluble in benzene and petroleum ether, sparingly soluble in chloroform and acetone, and soluble in tetrahydrofuran (THF), methyl ethyl ketone (MEK) arid dimethylformamide (OM F). Table 7 details the developed products. Table 8 summarises the molecular weight and polydisp~rsity of these products. The weight average molecular weight of these alkyds ranged from 1500 to 2600 (based on polystyrene standards). Table 9 shows the series of alkyds prepared by changing the amount of reactants and the type of catalysts under reduced pressure. Some of these resins were generally transparent, hard and brittle with softening temperature 70-120°C.

Table 7- Alk yd resins developed from BH ET (m .p . 110-1 12°C) with maleic anh ydride at 2 10-220°C and at atmospheric press ure

Product BHET: Maleic Catal ys t Nature of So lubility Adhesive

anhydride(w/w) product property o btained o n metal s

Alk-I 2.5: I No ne Sticky solid Aceto ne Not good C hlo rofo rm

DMF

Alk-2 2.5: I DAP Sticky so lid DMF Good

Alk-3 2.5: I TSP Stick y mass DMF G ood

Alk-4 2.5:2 No ne Sticky so lid Aceto ne Not good DMF

Alk -5 2.5:2 DAP Sticky solid Aceto ne Good DMF

Alk-6 2.5: 2 TSP Sticky solid Aceto ne G ood DMF

uAP- Diammoniull1 hydrogen phosph a te; TSP- Tri sodiull1 phospha te; DMF- Dimeth ylfo rma midc

19

Product

Alk-7

Alk-8

Alk-9

Alk-I O

Alk-II

Alk-12

Alk- 13

Alk-14

Alk- 15

Alk- 16

Alk -17

Alk-18

Alk-19

INDIAN J. FIBRE TEXT. RES., MARCH 1991

Table 8- Dispersity. mo lec ul ar size a nd molecula r weight of al kyd resi ns

Prod uct

Alk-I Alk-2 Alk-3 Alk-4 Alk-5 Alk-6

Molecula r size )I.

1683 1909 2069 2087 1765 1762

Molecular weight"

Mn Mw (No. avo (Wt. avo mol.wt) mo l.wt)

700 1579 11 27 2653 11 59 2627 886 2296 857 203 1 829 1970

"Calcula ted on the ba sis of po lys tyrene standa rds.

Dispersit y

M, Mw/ Mn M,jMn (Z-av.

mol.wt)

3247 2.25 4.64 5 147 2.35 4.56 4665 2.26 4.02 4045 2.59 4.56 3683 2.37 4.29 3554 2.37 4.29

Table 9- Alk yds prepared with BH ET (m.p. 11O-11 2"C) and maleic anhyd ride at 2 10-220"C under reduced pressure (40-50 mm of Hg)

BHET: Catalyst Nature of Softening Solubility Adhesive Maleic product temp. property an hyd ride obtained "C on metals (w/w)

1: 1 None Transpa ren t 120-130 THF, DMF Good hard solid

1: 1 DAP Sticky solid DMF Good

2: I DAP Transparent 11 0-130 DMF Good hard solid

2.5: I None Transparent 80-90 Ch lo roform Good hard solid Acetone

DMF

2.5: I DAP Tra nspa ren t 90-100 Ch loroform Good ha rd so lid Acetone

DMF

2.5: I TSP Hard solid 110-1 20 DMF Good

2.5: I DAr Transparent 120- 160 DMF Good hard solid

2.5: 1 DAP Transparent 100- 120 DMF Good ha rd solid

2.5:2 None Sticky solid 70-80 DM F Good Ch lorofo rm

2.5:2 DAP Hard solid 70-80 DMF Good

2.5:2 TSP Hard solid 90- 100 DMF Good

4:1 None Ha rd solid 110-120 DM F Good

5: I one Stick y solid 100-110 Acet()ne Good DM F

DAP- Di ammonium hyd rogen phospha te; TH F- Tetrahydrofuran; DM F- Dimeth ylfo rmamide; TSP--T risodium phosphate

20

BANDYOPADHYAY et at.: UTILIZATION OF POLYESTER WASTE

Table 10- Thermal studies of polyester degraded products and alkyds prepared from them

Prod uct

BHET (m.p. 110-11 2°C)

Mixed terephtha lates (obtained from the glycolysis by using ethylene glycol)

Mixed terephthalates (obtained from the glycolysis by using diethylene glycol)

Mixed terephthalates (obtained from the glycolysis by using propylene glycol)

Alk-I Alk-2 Alk-3 Alk-4 Alk-5 Alk-6 Alk-IO Alk-II Alk-12 Alk-15 Alk-16 Alk-1 7 Alk-19

IDT °C

250

255

265

280

200 190 225 160 175 155 270 280 250 170 160 175 255

Temperature at 50%

weight loss T

415

435

435

425

420 400 420 400 400 395 430 425 430 425 420 405 425

They were almost insoluble in petroleum ether and benzene and soluble in DMF and THF.

An attempt was made to prepare alkyd resins in situ (without separating BHET and mixed terephthalates) with maleic anhydride (1:1 weight ratio) in the presence of diammonium hydrogen phosphate under reduced pressure and elevated temperature. These alkyds were sticky and yellowish brown in colour. It was observed that 30-60 min reaction under vacuum could produce resins which can be easily dissolved in solvents like acetone and DMF. Table 10 shows the results of weight loss studies on the reaction products and on some of the alkyds prepared from these products. The study revealed that the developed alkyds were thermally quite stable and could be processed for speciality end uses.

A series of alkyds were also produced as reaction products of phthalic anhydride with BHET or with other low molecular products in situ. Tables II and 12 give the details of the products and their molecular weights. Phthalic anhydride could also produce different types of alkyds under different reaction conditions. Fig. 5 shows the possible chemical structure of alkyd produced with phthalic anhydride.

Attempts to produce the alkyds from the glycolyzed product of DEG, PG and PEG-400 with maleic acid /anhydride and phthalic acid/anhydride resulted in the development of hard and brittle resins of high molecular weight. These were soluble in THF

Table II - Alkyd resins prepa red using either BHET or glycolyzed total waste mass in situ with phthalic an hydride under red uced pressure a t 2 10-220°C

Product

Alk-I

Alk-2

Alk-3

Alk-4

Alk-5

Alk-6

BH ET/Glycolyzed waste: Phthalic anh ydride (w ... , )

BH ET Phthalic an hydri de ( I :2)

BH ET:Phthalic anhydride (I :2)

BH ET Phtha lic anhydride (5:3)

BHETPhthalic anhydride (5:3)

To tal glyeolyzed waste: Phthalic anhydride (I: I)

Total glyeo lyzed waste :Phthalie anhydride (I: I)

Catalyst

None

DAf>

None

DAP

None

DAf>

Nature of product obtained

Sticky solid

Tra nsparent brittle mass

Sticky solid

Transparent hard solid

Opaque white sticky mass

Yellowish brittle solid

So ftening temp.

°C

80-100

90-110

90-100

Solubility

DMF

Acetone DMF

DMF Chloroform

Acetone DMF

Ho t DMF

Acetone DMF

(contd.)

21

Prod uct

Alk -7

Alk-8

INDIAN J. FIBRE TEXT. RES .. MARCH 199 1

Table II - Alk yd resi ns prepared usin g either BH ET or glycolyzed total waste mass in Silu with

BH ET/G lycolyzed waste: Ph thai ic anh ydride (w/w)

Total glycolyzed waste: Ph t ha I ic anhydride (I :2 )

Total glycolyzed waste:Phthali c anhydride ( I :2)

phthalic anhydride under red uced press ure at 210-220°C (Contd .)

Catal ys t Nature of Softenin g

None

DAP

product temp. obtained T

Sti cky white soli d

Transparen t brit tle solid

100- 11 0

Sol ubility

Hot DMF

DMF

DAP- Diammoniu m hydrogen phosphate: DM r - Dimeth ylformam ide

Table 12- Dispersi ty. molec ula f size and molecular weight of a lkyd resins prepared usi ng ph tha li c anh ydride unde r reduced pressure

Sample Molec ula r Molecul ar weigh t Di spersity size

0

Mil M" M, M" iMn M,/ Mn A (No . av o (Wt av o (Z-av. mol. wt) mol. wt) mol. wt)

Alk- I 5539 2953 Alk-2 19 17 1269 Alk-3 3640 56 1 Alk-4 6436 1342 Alk-5 2500 1528 Alk-6 4434 2350 Alk-7 6078 3074 Alk-8 7522 2755

~o- ~ HO - CH: - CH2 - 0 - C \ ~ j C - 0 - ~ Hl - CH I - OH +

9H£ T

Phthalic Anhy~1(M'

"t "0" -'"> - '"> - ""' 0 '"" -'"> - '"> - " t" In" IS I

A lkyd

Fig. 5-Chemica l structure of alk yd with phthalic anhyd ride

and DMF. A few linear a lkyds were also synthesized with adipic acid a nd BH ET under different reac tio n conditions. These a lk yds had varying melting points.

22

6235 2245 3382 6908 2968 5095 6790 786 1

9963 5555 7038

15903 4766 822 1

10851 13918

NCO

CH) O NCO +

TD !

NCO

2. 12 3.39 1.76 2.80 602 12.53 5. 14 11.84 1.94 3. 11 2. 16 3.49 2.20 3.52 2.85 5.05

OH - CHI - CHI - 0 - ~ -0 ~ -OCHICHIOH

BHET

CH) 0 NH - coo - CHICHI - DOC 0 coo - CHI - CHI - OH

Without I w ith Chain E.tvnd~r

Cross linked and HIgh mol. wt. Pu

FIg. 6- Chemical structure of PU resin

A series of uretha ne precondensa te resins (PUl were prepared using BHET a nd other glycolyzed products with tolucnc-2,4-di-isocyanate (TD I). Fig. 6 shows the chemical structure of P U resi n. The chai n extender such as PEG-400, glyce rol , ethylene

BANDYOPADHYAY el at.: UTILIZATION OF POLYESTER WASTE

glycol, etc . were used. The developed polyurethane resins were purified and characterized . Table 13 shows the characteristics of some of the products. Some PU resins were a lso prepared by solution polymeri za tion using dimethylsulphoxide as a solvent. The studies showed that the molecular

weight of polyurethane resins depended on the concentration of reactants ra ther than on the duration and temperature of the reaction .

7 Application Areas The wide range of a lkyds and urethane resins

Table 13- Di spersity. molecula r size a nd mo lecular weight o f urethanes prepared by using tol uene-2.4-di-i socyanate

Reactants Sp.gr. Molecular Molecular weight Di spersity

(mola r ratio) °Tw size A Mn Mw M, Mw/Mn M,/Mn

(No. avo (Wt.av. (Z-av. mo l.wt) mo l. wt) mol. wt)

BH ET + TD I + PEG-600 49 16 18 1591 2255 3 185 1.41 2.00

( 1:0.6:0.5)

BHET + TDI + PEG-600 1909 522 1·939 3720 3.7 1 7. 12

(1:0.6:0.5)

Table 14- Mechanical properties of nonwoven treated wi th a lkyd"

Substrate Application Add-on Tensile strength . kgf Air permeability method % mJ/m2/min

Machine Cross ( 10 mm water direction direction column)

Po lyester/Vi scose 8.6 14.3 68 (50:50). 310 g/m2

Saturation 18 19.8 25.3 69.3

Viscose. 310 g/m2 7.8 10.6 36 Saturation 13.6 9.2 18.3 29

Spray 3 8.4 14.2 37 (One side) Saturation 38 17 25 24

aprepared using maleic anhydride a nd BH ET in the rat io 2.5 :2

Table 15- lncrease in breaking strength o f urethane coated fabrics

Substrate C hemical Applica ti on Chemica l Increase in method add-on breaking

% strength %

Po lyes ter. 300 g/m2 PU- I Spray 14 70 Po lyester. 300 g/m2 PU- I Sa tura ti o n 38 140 Polyes ter/Vi scose PU-I Saturation 42 160 (50:50). 300 g/m' Po lyes ter: Viscose PU-3 Sa tura tio n 36 130 (50:50). 300 g/m'

Viscose. 3 10 g/m2 PU-2 Saturation 16 63 Viscose. 3 10 g/m2 PU-2 Spray \I 38

(Both sides) Po lyester:Viscose PU-2 Spray \I 46 (5050). 300 g/m' (Both sides)

and thermal bonded

23

INDIAN J. FIBRE TEXT. RES., MARCH 1991

produced were evaluated for a number of possible applications. Many of these products were found to be useful for paint, varnish, adhesive, insulation and related areas. Amongst the textile uses , they were found to be useful for coating and finishing of woven and non-woven fabrics 2 7 ,28. The mechanical properties of some of the developed products are given in Table 14. It shows the increase iri strength of the fabric , both in machine and cross direction, depending on the percentage add-on. The air permeability, which is an important factor, decreased substantially. Table 15 shows the increase in breaking strength of urethane coated fabric. PU resins were dissolved in solvent and application was carried out either by saturation or by spray. The breaking strength invariably increased for all the samples with these urethanes.

8 Conclusions The studies made have shown that it is possible to

recycle the polyester waste either to produce basic monomers Qr to convert the depolymerized products to alkyds and urethanes. These resins can be used for a number of applications and admixed with various types of chemicals and auxiliaries to produce different products for commercial uses.

Acknowledgement The authors are grateful to the Ministry of Textiles,

Government of India, for sponsoring the research project. Thanks are also due to Dr S M Betrabet, Director, BTRA, for permission to publish this paper. The help rendered by various polyester fibre manufacturing companies by supplying different types of waste material IS also gratefully acknowledged.

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24

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