Fb 2014 Tapia

Fibers and Polymers 2014, Vol.15, No.3, 547-552

547

Polyester Fiber Production Using Virgin and Recycled PET

J. C. Tapia-Picazo*, J. G. Luna-Brcenas, A. Garca-Chvez1, R. Gonzalez-Nuez

2,

A. Bonilla-Petriciolet1, and A. Alvarez-Castillo

3

Cinvestav-Quertaro, Libramiento Norponiente 2000, Fracc. Real de Juriquilla, Quertaro, Quertaro., C.P. 76060, Mxico1Chemical Engineering and Biochemical Department, Technological Institute of Aguascalientes,

Aguascalientes, Aguascalientes, C.P. 20256, Mxico2University Center of Exact Sciences and Engineering, Chemical Engineering Department, University of Guadalajara,

Guadalajara, Jalisco, C.P. 44430, Mxico3Division of Graduate Studies and Research, Chemical and Biochemical Engineering Department, Electromechanical

Department and Basic Sciences Department, Technological Institute of Zacatepec, Zacatepec,

Morelos, C.P. 62780, Mxico

(Received August 30, 2012; Revised July 9, 2013; Accepted July 30, 2013)

Abstract: In this study, the design and construction of an extrusion equipment with spinning fiber devices has beendeveloped to produce polyester fiber from virgin and recycled polyethylene terephthalate (PET). Several operatingparameters (i.e., pressure, temperature, feed flow rate, extrusion speed and extruder design) have been analyzed to identifythe best process conditions. In particular, this study has focused on a detailed analysis for the processing of recycled rawmaterial for polyester textile fiber applications considering the variability of the process and identifying alternatives tominimize the impact on the quality parameters such as the fiber diameter and mechanical specifications. The experimentalresults were compared with the values calculated using a theoretical model, which has been developed for these particularcases. The mathematical analysis of the mass flow showed a very good agreement with respect to the experimental data,where there was a percentage difference < 3 %. It was found that the fiber diameter is a function of intrinsic viscosity (VI) ormelt flow index (MFI). Finally, the mechanical properties of the fibers were evaluated and results indicated that the fiber withhigher average molecular weight showed higher tenacity and lower Youngs modulus values.

Keywords: Recycled PET, Extrusion process, Spinning fiber, Textile PET fiber, PET

Introduction

From an economical point of view, the recycling process is

the best way to reduce wastes of poly(ethylene terephthalate)

(PET) [1] and, therefore, many technologies have been

developed for performing this type of processes. The first

effort in the world for recycling PET bottles was in 1977 [2];

but in the following decades, scientific studies were performed

to analyze the properties of recycled PET wastes using

extrusion processes. Several methods have been reported to

obtain recycled recipients and bottles from PET, but in

general PET wastes have been traditionally used for energy

recovery [3-5]. Actually, the recycled PET is used in the

synthesis of special plastic composite materials [6] and to

reinforce concrete [7,8]. For example, Torres et al. [9]

performed a comparative study of the thermal and mechanical

properties of bottles made from waste and virgin PET. These

authors have obtained elongation values of 200 % for virgin

PET and values 10 % smaller for recycled PET. These results

were attributed to the crystallinity differences. Oromiehie

and Mamizadeh [10] used three different methods for recycling

PET bottles, where virgin PET, recycled PET and mixtures

of both PET types, with and without polypropylene

functionalized with maleic anhydride [PP-graft-MA]), were

processed. This study reported that the intrinsic viscosity

(IV) and molecular weight (Mw) decreased with the content

of the recycled PET in the mixtures. This behavior was

attributed to thermal effects, as well as, the mechanical

degradation of recycled PET. In addition, the properties of

the functionalized blends were improved due to the chemical

and physicochemical interactions between components in

the blend. On the other hand, Martin and Rojas [11] developed

an extrusion process for the production of recycled PET

filaments using a simple screw. This patent consisted of two

parts. The first one is related to the recycling of PET with a

stirrer and a condenser, while the second one involves the

extrusion process itself. This development was performed to

obtain a constant quality in the extruded product, which

corresponds to the main problem in the traditional PET

extrusion recycling.

It is convenient to remark that several studies have reported

that raw material flakes produced by the size reduction of

PET waste should have certain minimum requirements in

order to achieve a satisfactory PET recycling process [12-

15]. This is because there is a loss of molecular weight in

PET extrusion process due to hydrolytic [16,17] and thermal-

mechanical degradation during melting process [18].

Degradation also causes non uniformity in the flow of fused

material generating negative effects in subsequent processes*Corresponding author: [email protected]

DOI 10.1007/s12221-014-0547-7

548 Fibers and Polymers 2014, Vol.15, No.3 J. C. Tapia-Picazo et al.

and the properties of final product are also affected [4].

Gurudatt et al. [19] obtained chips from PET waste for the

filament extrusion process. Virgin PET and waste PET from

bottles were used in mixtures of different compositions.

These authors analyzed the extrusion and stretching stages

of the spinning process and found that the variations of

molecular orientation is very important for determining the

properties, efficiency and production of final fiber. Abbasi et

al. [20] showed that the crystallinity of recycled materials

was higher than those obtained for virgin materials.

Consequently, the tenacity of samples from used material

was higher and the elongation was smaller. Herein, it is

convenient to highlight that there are other scientific and

industrial reports about the production of fibers from

recycled PET [21-24]; unfortunately, the technical details

are not described because of the industrial secrecy.

In this study, an analysis of the critical variables that

impact on the flow uniformity of the melt polymer and the

degradation of recycled PET using an extruder was performed.

This study includes the following aspects: a) the design of

the PET extrusion and spinning process for textile applications,

b) the mathematical analysis of the operation curves in the

extrusion process, c) experimental results and the material

characterization in the extrusion and spinning stages, and

finally, d) the validation of the operation curves using the

experimental data.

Methodology

Process Design

The process design was based on the process specifications

and final product (i.e., textile fiber) and they include: the

operation temperature: 270-320 oC, the drying temperature:

70-140oC, the maximum PET humidity percentage: 0.02 %,

the fiber tenacity: 2 gf/denier, the elongation: 20 %, the

residual retraction: < 5 %, and the product denier: 1.5-3. For

the screw design, the properties of the raw material and the

design parameters (e.g., compression ratio, residence time,

angles of the helix, the relationship length/diameter of the

extruder) were considered and they values were established

according to the literature [11,25].

Mathematical Analysis

Mathematical equations for the process design analysis

were adapted to the extruder and raw materials used in the

present communication. These equations were based on the

PET degradation during reprocessing and the results reported in

[25]. Specifically, the total flow equation (Q) inside the

extruder was obtained by solving the moment, heat and mass

balances. This problem was considered as a fluid movement

between two surfaces, in which one of them is movable

(screw) and using a rectangular coordinate in z direction

(channel of the screw). Then, the total flow is given by

(1)

where N is the screw rotation speed, P is the pressure drop, is the melt viscosity of the material; while D, H, L and

are the diameter, depth, length and angle of the screw,

respectively. The melt viscosity is considered a function of

the inherent viscosity (IV) and absolute temperature (T) and

it is given by

(2)

During processing, the degradation of the PET material

occurs due to chain scission, causing a decrement of the

average molecular weight, which is measured by the inherent

viscosity at any residence time in the melt (IVt). This

function is given by the following equation

(3)

where T is the absolute temperature, IV0 is the initial

inherent viscosity, and t is the residence time in the melt,

respectively.

On the other hand, if the PET polymer contains some

water, the hydrolytic degradation may also occur and can be

calculated by

(4)

where IVH is the inherent viscosity after reaction with water,

IV0 is the initial inherent viscosity of supplied PET polymer

and x is the % weight of water in supplied PET polymer,

respectively.

The analysis was performed by taking into account the

degradation and the material uniformity in the process. For

this purpose, we have used the strategy and method reported

by Franceschini and Macchietto [14]. Therefore, a complete

factorial experimental design and mathematical calculations

of the operation curves were performed. The analysis was

performed considering the variation levels for recycled PET

in the following critical ranges [9,11,13,25-27]: a) mass flow

variation: 10 %, b) pressure drop: 10 %, c) intrinsic

viscosity: 0.8-0.5, and d) raw material humidity:

Polyester Fiber Production Using PET Fibers and Polymers 2014, Vol.15, No.3 549

before the test evaluation. The pressure was fixed for every

experimental test using different screw speeds. The mass

flow was determined at different pressure conditions (from

2.68 to 4.14 kg/cm2) and temperatures (i.e., 260, 280, 290

and 300oC) for the two different raw materials: recycled

PET (VI=0.65) and pharma grade PET (VI=0.71). The results

obtained from the mathematical modeling were compared

with those obtained from the experimental tests.

Finally, the fibers obtained using virgin and recycled PET

were mechanically characterized. Specifically, the tensile

properties were determined using an Instron machine (model

4011) in accordance with ASTM D 638-10. Also, the average

molecular weight was evaluated using the viscosimetric

approach and the micrographs were obtained using a

scanning electron microscope HITACHI TM-1000.

Results and Discussion

Process Design

The extruder is based on a normal design but it has an

adjustable support for the motor that allows the screw to be

removed in just one minute for analyzing the changes of

material inside the barrel at different process conditions [28].

To remove the screw, the gear box has two dissembling

gears than permit to separate them with a single bolt. Latter,

the motor is moved on the adjustable support for taking out

the screw in a direction opposite to the material flow. In the

spinning stage, first a slow stretching and a second stretching

are applied to the polyester fiber using three groups of five

rollers. This operation improves the molecular orientation

and crystallinity in order to increase the mechanical properties

of the polyester [19,25]. Two drying systems were used to

improve the crystalinity, dimensional uniformity and to

reduce fiber porosity [25]. One drying system used heat rolls

and the other included three heat plates operating at

temperatures between 10 and 100 oC over the glass transition

temperature of PET. The same operating conditions were

used in extrusion and spinning stages and the virgin and

recycled PET were processed at the values reported in Table 1.

Tensile Mechanical Properties

The tensile mechanical properties of the fibers are

reported in Table 2. The break stress of the virgin PET fiber

was higher than the value obtained for the recycled PET

fiber; while its Youngs modulus was lower (almost 50 %).

The break elongation values found in this study are very

near to the values reported in other studies [29,30]; while the

breaking stress and Youngs modulus are lower than the

values reported by Wrbel and Bagsik [30] and Frounchi et

al. [31] but in the same order of magnitude. To explain these

differences, the average molecular weights of virgin and

recycled fiber were calculated using the intrinsic viscosity

approach. The average molecular weights of virgin and

recycled fiber were 19342 g/mol and 15813 g/mol, respectively.

According to literature, the presence of smaller polymer

chains, due to the polymer degradation, may be are not

accommodated than the larger chains. This can cause a

decrement of the crystallinity, which has a significant influence

on the mechanical properties. Therefore, the fibers with

lower average molecular weight may show lower break

elongation, higher Youngs modulus [29,30] and a lower

breaking stress [30]. Flow index of raw materials used in the

extrusion process was obtained, see Table 3. The difference

in flow index is mainly caused by the hydrolytic degradation

that the extrusion process produced to the recycled PET;

therefore, an increase in the melt flow is an indicator of the

extent of the thermo-mechanical degradation [32].

Figure 1 shows the micrographs of virgin and recycled

PET fibers obtained at different magnifications. The surface

morphology of the virgin fibers consists of smooth cylindrical

fibers. It appears that this smooth surface is caused by the

partial solidification that occurs as soon as the fiber leaves

the extruder [33]. Experimental studies have reported that

the viscosity of the PET polymer has a significant impact on

the fiber diameter than any other process variable [34].

Therefore, different average diameters should be obtained

for virgin and recycled PET (see Figure 1). In fact, virgin

fibers showed a lower diameter than that obtained for

recycled fibers. This is because the lower flow mass of the

virgin PET at the process temperature, caused principally by

the lower flow index of the raw material in comparison to

Table 1. Operation conditions for processing virgin and recycled

PET

Condition Value

Residence time 10 minutes

Extrusion temperature 280 oC

First stretching 1.5 times

Second stretching 1.5 times

Drying temperature 120 oC

Spinning speed 50 m/minute

Table 2. Mechanical properties of virgin and recycled PET fibers

Property Virgin PET fiber Recycled PET fiber

Tensile strength (kg/cm2) 140.5 220.0

Breaking stress (kg/cm2) 82.2 42.20

Break elongation (%) 6.96 5.00

Youngs modulus (kg/cm2) 5690 10500

Table 3. Melt Flow index of virgin and recycled raw materials

Raw material Melt flow index (g/10 minutes)

Virgin PET 13.21

Recycled PET 21.34


Figure 1. Micrographs of PET fibers obtained with, (a),(c) virgin PET and (b),(d) recycled PET at the operating conditions given in Table 1.

Table 4. Geometry and extruder operating conditions

Extruder zone Feeding Compression Dosing

Diameter (cm) 3.33 3.33 3.33

Length (cm) 33 33 34

Depth (cm) 0.6 0.38 (average) 0.16

Angle () 17.2 17.7 15

Operating temperature (C) 280 285 290

Figure 2. Flow behavior inside the extruder obtained with

equation (1).

the recycled material. Additionally, the surface of virgin

fibers has lower defects and higher shining than those

obtained for the recycled fibers.

Mathematical Analysis of the Process

Equation (1) was used for the calculation of the flow rate

(Q) using the geometry and extruder operating conditions

given in Table 4. We have considered a standard PET

extrusion process with an initial intrinsic viscosity of 0.6, a

mass flow in the feed of 99 g/minute, L/D extruder ratio of

30 and an extruder diameter of 0.033 m. Figure 2 shows the

behavior of the flow along the extruder length. The changes

of density or flow rate were produced by the temperature

and the geometry of the extruder. Note that these changes

were more significant in the first two sections at the same

speed of change even though these sections showed differences

in the geometry and temperature. On the other hand, the

pressure along the screw was affected mainly by its

geometry in the last extrusion zone. For the case of the

extrusion process of recycled PET (Figure 3), this increasing

pressure was mainly caused by the total fusion of the

material and the geometry in the last 0.34 m of the extruder.

If an increment of 10 % of mass flow variation in the feed is

considered, the pressure does not present a considerable

Polyester Fiber Production Using PET Fibers and Polymers 2014, Vol.15, No.3 551

change inside the extruder for the first two sections, but for

the last zone (compression) the pressure may present a

significant variation, see Figure 3. This is an important issue

to be considered in the control of the system because this

level of mass variation is a normal value in the recycling

process and it will affect the final diameter of the filaments

produced using this type of extruders. The normal variations

for the filament diameter are 10 % and this is the reason for

minimizing the mass variation using the pressure control of

the screw.

Based on the results of the operation curves, we can define

that the variability of VI0 in the range of 0.5-0.8 must be

reduced using the appropriate raw materials to produce a

quality product. On the other hand, it is necessary to handle

the following operating variables: a) screw speed: 30-

45 rpm, b) temperature: 270-300 oC and c) humidity: 0.01-

0.02 %.

Experimental Test

Figure 4 shows the relationship of the flow with respect to

the pressure applied to the extruder for different temperatures

of the extrusion process using pharma grade recycled PET.

At 290oC, the mass flow variation is not so sensitive to

pressure changes in the extruder. For the case of bottle grade

recycled PET, the mass flow showed a minimum variation at

280oC regarding the analyzed operating pressures. Finally,

the experimental data were used for validating the mathe-

matical model and Figure 5 shows the experimental mass

flow of the pharma grade recycled PET and the respective

calculated mass flows. The predicted results are very close

to experimental data with a maximum error of 3 %. This

result indicated that the model used to describe the performance

of experimental set up is adequate.

Conclusion

In this study, we have reported a screw design that

includes an appropriate handling of flows and pressure drop

inside the extruder and adequate design parameters for

recycling PET. This design includes a spinning system,

which is based on current technologies for the development

of special fibers. Results of the mathematical analysis were

used to identify the quantitative impact of the characteristics

of the raw material, pressure, temperature, feeding flow,

extrusion speed and design of the extruder on the performance

Figure 3. Pressure inside the extruder of a standard PET extrusion

process with a flow rate variation of +10 %.

Figure 4. Mass flow as a function of pressure and temperature for

recycled pharma-grade PET.

Figure 5. Comparison of the experimental and calculated values

of mass flow.


of the extrusion process of recycled PET. The mathematical

prediction of the extruded mass flow is in good agreement

with the experimental data with a maximum error of 3 %.

Finally, the recommended operating conditions for textile

applications and the principal characteristics of raw recycled

material are: VI0: 0.5-0.8, screw speed: 30-45 rpm, temperature:

270-300 oC and humidity: 0.01-0.02 %. These operating

conditions are important to control the variation levels than

the recycled PET normally shows in extrusion process.

References

1. B. Kuczenski and R. Geyer, Resour. Conserv. Recycl., 54,

1161 (2010).

2. F. La Mantia and M. Vinci, Polym. Degrad. Stab., 45, 121

(1994).

3. F. Daw-Ming, S. K. Huang, and L. Jiunn-Yih, J. Appl.

Polym. Sci., 61, 261 (1996).

4. I. A. Abu-Isa, C. B. Jaynes, and J. F. O'Gara, J. Appl.

Polym. Sci., 59, 1957 (1996).

5. B. Saha and A. K. Ghoshal, Chem. Eng. J., 111, 39 (2005).

6. Y. Zou, N. Reddy, and Y. Yang, Compos. Part B-Eng., 42,

763 (2011).

7. F. Fraternali, V. Ciancia, R. Chechile, G. Rizzano, L. Feo,

and L. Incarnato, Compos. Struct., in press, Corrected

proof (2011).

8. D. Foti, Constr. Build. Mater., 25, 1906 (2011).

9. N. Torres, J. J. Robin, and B. Boutevin, Eur. Polym. J., 36,

2075 (2000).

10. A. Oromiehie and A. Mamizadeh, Polym. Int., 53, 728

(2004).

11. J. Martn and M. Rojas, Patent and Trademark Spanish

office (OEPM), 2226512 (2005).

12. K. S. Seo and J. D. Cloyd, J. Appl. Polym. Sci., 42, 845

(1991).

13. A. Cata, G. Bandur, I. Balcu, D. Buzatu, C. Tanasie, and D.

Rosu, Chem. Bull. POLITEHNICA Univ. (Timioara),

52, 143 (2007).

14. G. Franceschini and S. Macchietto, Ind. Eng. Chem. Res.,

46, 220 (2007).

15. S. D. Mancini, J. A. S. Schwartzman, A. R. Nogueira, D.

A. Kagohara, and M. Zanin, J. Clean Prod., 18, 92 (2010).

16. E. Pirzadeh, A. Zadhoush, and M. Haghighat, J. Appl.

Polym. Sci., 106, 1544 (2007).

17. H. Saeid, S. Taheri, S. Zadhoush, and A. Mehrabani-

Zeinabad, J. Appl. Polym. Sci., 103, 2304 (2007).

18. F. Samperi, C. Puglisi, R. Alicata, and G. Montaudo,

Polym. Degrad. Stab., 83, 3 (2004).

19. K. Gurudatt, P. de A. K. Rakshit, and M. K. Bardhan, J.

Appl. Polym. Sci., 90, 3536 (2003).

20. M. Abbasi, M. R. M. Mojtahedi, and A. Khosroshahi, J.

Appl. Polym. Sci., 103, 3972 (2007).

21. D. M. Juriga and R. E. Allen, U. S. Patent and Trademark

Office Pre-grant Publication, US20080292831 (2008).

22. J. Brownstein and K. Brownstein, Patent Cooperation

Treaty Application, US20110030557A1 (2011).

23. M. W. Coates, M. H. Kierzkowski, P. J. Gibbons, and A. J.

Eiden, Patent Cooperation Treaty Application, WO10063079

(2010).

24. M. C. Thiry, AATCC Rev., 20 (2009).

25. R. G. Dale, Int. Nonwovens J., 9, 15 (2000).

26. L. Incarnato, P. Scarfato, L. Di Maio, and D. Acierno,

Polymer, 41, 6825 (2000).

27. F. Awaja and D. Pavel, Eur. Polym. J., 41, 1453 (2005).

28. A. Garca and J. C. Tapia, Master Thesis, Technological

Institute of Aguascalientes, Aguascalientes, Mxico, 2008.

29. S. D. Mancini and M. Zanin, Mater. Res., 2, 33 (1999).

30. G. Wrbel and R. Bagsik, J. Achiev. Mater. Manuf. Eng.,

43, 178 (2010).

31. M. Frounchi, M. Mehrabzadeh, and R. Ghiaee, Iran.

Polym. J., 6, 269 (1997).

32. M. A. Silva-Spinac and M. A. De Paoli, J. Appl. Polym.

Sci., 80, 20 (2000).

33. J. Lyons, C. Li, and F. Ko, Polymer, 45, 7597 (2004).

34. H. Rajabinejad, R. Khajavi, A. Rashidi, N. Mansouri, and

M. E. Yazdanshenas, Int. J. Envir. Res., 3, 663 (2009).

/ColorImageDict > /JPEG2000ColorACSImageDict > /JPEG2000ColorImageDict > /AntiAliasGrayImages false /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 150 /GrayImageDepth -1 /GrayImageDownsampleThreshold 1.33333 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict > /GrayImageDict > /JPEG2000GrayACSImageDict > /JPEG2000GrayImageDict > /AntiAliasMonoImages false /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 150 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.33333 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict > /AllowPSXObjects false /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputCondition () /PDFXRegistryName (http://www.color.org) /PDFXTrapped /Unknown

/Description >>> setdistillerparams> setpagedevice

Documents

Fb 2014 Tapia