Effect of Solvent Pretreatment of Polyester at Varying Temperature and Time on the Glass Transition Temperature

Effect of Solvent Pretreatment of Polyester at Varying Temperature and Time on the Glass Transition Temperature

* Adeakin O. A. S 1, Ajekwene K. K.3

1,3 Department of Polymer and Textile Technology, Yaba College of Technology,

Lagos, Nigeria.

Popoola V. A 2

2 Department of Chemistry, Federal University of Technology, Akure, Nigeria.

Abstract – The glass transition temperature of a polymer such as Polyethylene terephthalate is found to alter significantly as a result of modification to its structure. Polyethylene terephthalate was pretreated in ten organic solvent at 30oc and 50oc for 30, 60, 120, 300 and 900 seconds respectively. The Tg of the samples were tested which was found to alter significantly with marked results obtained on samples treated with Benzyl alcohol.

Key words: Polyester, Solvents, Pre-treatment, Glass Transition Temperature (Tg)

INTRODUCTION

The transition temperatures of polymers are very important to determining the behaviour of the polymers at production, processing and use. They serve as guide into how the polymer performance can be predicted. The identifiable transition temperatures are: the glass transition temperature (Tg), melting temperature (Tm), crystallization temperature (Tc) and degradation temperature (Td). The peculiarities of these temperatures are significant. The gap difference between the glass transition temperature (Tg) and the next transition temperature (Tm) is very wide. The lower the Tg for polyethylene terephthalate (PET) and the easier it is for processing handle where heat application is required. As a result of this, chemists try to work on this aspect either physically or mechanically or chemically or a combination of both. Chemical treatment leading to physical or mechanical modifications are the target of this study.

The physical states of a polymer have been identified to change as a result of treatment given to the polymer. Solvent treatment on polyester have been studied by a number of workers as a means of ensuring detailed study of the polymer characteristics. Popoola 1983, studied the effect of DMF treatment on polyester structures. Brenneck and Richter 1959, studied the swelling of polyester in various organic solvents. The glass transition temperature Tg is the onset of extensive molecular motion in an amorphous region. Tg is the most important parameter of an amorphous polymer, for it determines whether the materials will be hard solid or an elastomer in conventional use and at what temperature the behaviour changes. It is very important in partially crystalline polymers since it frequently gives an indication of an embrittlement temperatue. Polyethylene terephthalate (PET) is a 35-49% crystalline in nature with no positive or negative charges in its structures. The polymer is hydrophobic with less than 1% moisture absorptive capacity which exhibits very small extent of swelling in water of which most of its treatment processing takes place (Walawska, ettal, 2003).

MATERAILS AND METHOD

The polyethylene terephthalate polymer fibre used for this study was treated in a 3- neck solvent treatment flask at 30oc and 50oc for 30s, 60s, 120s, 300s and 900s respectively. The samples are then dried at 70oc and the glass transition temperature determines using a melting point apparatus.

Tg (oC)

RESULTS / DISCUSSION

100

90

Cont

80

Chlo

70

Acet.

60

Benzald.

50

Nitro.

40

D-O-P

30

Cyclo

nHex

0

0

500

1000

Time of Treatment(s)

1500

2000

D-O-P

40

Benzald.

70

60

Acet.

10

DMF

Benz.Al

20

Tg oC

Figure 1 showing the Measured Tg at 30oC Pretreatment Temperature

100

Cont

90

Chlo

80

50

Nitro.

30

Cyclo

20

DMF

10

Benz.Al

0

mCre

0 500

1000

Time of Treatment(s)

1500

2000

nHex

Figure 2 showing the Measured Tg at 50oC Pretreatment Temperature

The effect of the amount of liquid retention on the measured Glass Transition Temperature (Tg) is a function of temperature of treatment but time and principally the amount of liquid retained. The attributes of the control (i.e untreated samples) shows that the glass transition temperature is about 90oC. The high Tg value is due to the effect of drawing and texturising on the development of crystallinity in the untreated fibre. A mixture of highly crystalline and amorphous regions are obtained due to the texturisation state of the original sample. The structure is probably micellar with deformation concentrated in the amorphous regions mainly.

At 30oC pretreatment temperature, the measured glass transition temperature (Tg) was least for benzaldehyde and dimethyl-o-phthalate i.e 66oC after 900seconds solvent interaction. However, at 50oC pretreatment temperature the least value was 62oC for chloroform, acetone, nitrobenzene, and benzyl alcohol. This is an indication that at higher temperature of solvent treatment, there is a greater segmental friction or mobility, which influences the rate of all configurational rearrangements of the polymer fibrillar structure similar to the observation of Williams etal, 1955. The glass transition temperature (Tg) of polyester cannot be observed from the two components of aliphatic sequence chains O.CO.CH2CH2.CO.O- while the higher glass transition temperature will be attributed to the benzene rings which are stiffer and probably interact together. The drop observed in figures 1 and 2 from 90oC for untreated to 74oC and below in the various solvents were as a result of chain strain which the polymer fibrillar structures were relieved off by the action of solvents. This

is observed to be highest for benzyl alcohol at 50oC pretreatment temperature. The lower the measured temperature i.e Tg, the better the polymer state prior to dyeing and the lower the temperature at which the processing temperature of dyeing can be carried out.

CONCLUSION

As a result of solvent treatment of the polyethylene terephthalate lower Tg is achieved. Solvent pretreatment at lower temperatures lowers the Tg minimally while at 50oc greater segmental friction or mobility of the polymer molecules is achieved which influences the rate of all configurational rearrangements of the polymer fibrillar structure. Relief of chains strains as a results of solvent action is prevalent at higher temperatures.

REFERENCES

1. Wakida T., Tomihara Y., Aoki I. and Kuroki N, Effect of Medium on the Structure of Nylon 6 and Polyester Fibre Treated by Microwave Heating, 1975

2. Popoola A.V., PhD Thesis, the effect of heat of liquid treatment on the structure and properties of of polyethylene terephthalate, 1983.

3. Brennecke W. and Richter H., Die Eigenschaften der Polyesterfaser Diolenr bei thermischen und chemischen Einwirkungen, Melliand Textilber, 40, p531, 1959

4. Walawska A., Fillipowska B. and Rybicki E., Dyeing Polyester and Cotton Polyester Fabric by means of Direct Diestuff after Chitosan Treatment. Fibres and Textiles in Eastern Europe, Volume II, No 2 (41) 71, 2003.

5. Williams M.L., Landel R.F. and Ferry D.J., Journal of American Chemical Society, 77, 3701, 1955.