INTRODUCTION
PET is a low cost, high performance semi-crystalline thermoplastic polymer with excellent properties. PET is used in textiles, reinforcement of tyres and rubber goods, and food and beverage packaging or for like filtration medias like filter bags.  

However, for industrial applications PET should have superior mechanical properties and dimensionally stable structure. In other words the fiber should attain adequate crystallinity and orientation for its use in industrial application. Crystallinity and orientation are achieved by drawing and heat setting. In this study, we report the effect of microwave irradiations on yhe crystallinity of PET fibers. Microwave irradiation has been successfully applied to a number of classical reactions2-6. The most important advantages of microwave irradiations are that it is a non-contact, localized, rapid, uniform, energy saving and pollution free heating process. The textile industry has extensively investigated uses of microwave energy for heating, drying, dye fixing, and finishing7-10. The Bombay Textile Research Association (BTRA) has also studied the applications of microwave energy in various areas of textile processing11-12. Heating materials using microwave radiations is limited to substances that can absorb this radiation and in turn dissipate this excess energy in the form of molecular oscillations. Materials, which absorb microwave radiations, are called “lossy”.

Unfortunately, textile materials are not heated to any great degree when so irradiated, and must be surrounded by a medium (lossy) capable of generating heat when exposed to microwaves. In our earlier studies13 we describe selection of lossy and their importance. The study mentioned in Reference 13 covers about 8 different liquids and on the basis of heat generated, glycerol was found to be the best. In the present work we exposed polyester filament yarn to microwaves for different time intervals and characterized them by X-ray diffraction (XRD). The results are compared with samples heat set in silicone oil for same time of intervals.

EXPERIMENTAL
Materials and Sample Preparation(e.g. syringe filters)

The starting material was a partially oriented (POY) multifilament PET yarn of 126 denier, 34 filaments. This sample was supplied by M/s. Reliance Industries Ltd., and referred to as the parent. Experiments were conducted in a multiwave LG Microwave Oven at 2450 MH frequency and 850 W power output. These PET-POY yarns were stretched to a draw ratio
of 1.6x using a small rectangular stretch frame at 85oC in a water bath. The rate of stretching was 4.7 m. /min. which was kept constant through out the stretching process for all samples. These drawn yarns were referred to as the control sample. The drawn yarns were removed from the stretch frame and wound immediately on a test tube manually, to minimize the relaxation of molecular chains. This test tube was immersed in another test tube containing lossy liquid and exposed to microwave radiations for time intervals of – 15, 30, 60, 90, 105 and 120
seconds. For each sample fresh lossy was used and the amount of lossy was kept constant. The sample after microwave treatment was taken out and cooled to room temperature. After cooling, the samples were washed with water to remove lossy and dried in air.
Another set of samples was prepared in silicone oil at 180 °C by conventional heating for same time intervals. After cooling, silicone oil from the surface was removed by using blotting paper, then washed with carbon tetrachloride (CCl4) and dried in air. Conventional heating was done in an electrically heated silicone oil bath. Whenever we use microwave heating the liquid used was glycerol. For conventional heating the liquid used was silicone oil. X-ray Diffraction Studies
The wide angle x-ray diffraction (WAXD) information was obtained on a Philips, XRD PW-
1720 unit fitted with a texture goniometer. Samples were scanned using Nickel-filtered Cu Kα, X-rays of wavelength 1.5418 A°, generated at 35 kV / 20 mA current. The multifilament yarn samples were arranged parallel to each other and mounted on the sample holder. Equatorial scan was obtained from 2= 10° to 35 °. WAXD measurements were used to calculate the crystal size, lateral order (LO) or crystallinity and crystallite orientation angle for samples exposed to mw radiations and heat-set in silicone oil. For POY yarns where single broad peak
occurs, WAXD was used to calculate the crystallinity index(CI).
Lateral Order Factor The LO factor, which can be related to crystallinity, perfection and size of crystallites, was calculated from the resolution factor (RF) by using the equation 14 RF = n n h h
m m m.......................2 ..................1 21 2 1(1)
where m1, m2, mn are heights of minima and h1,h2 hn. are heights of maxima from the base- line. For PET the resolution factor can be written as RF =1 2 31 2 2h h hm m
(2)where m1 and m2 are the minima between the planes (010) and (110) and between the planes (110) and (100) respectively; h1, h2, h3 are the observed maxima diffraction peaks of the planes (100), (110), and (010) respectively. Order Factor (OF) was calculated by  subtracting the RF from one. O. F. = 1- RF (3) Crystallinity Index In the case of amorphous samples (POY yarn) where a single broad peak occurs the crystallinity index was calculated from the fixed count measurements at 28.6° and 26° using the equation 15.
Intensity at 26°x 100 Crystallinity Index = (4) Intensity at 28.6° Crystallite Orientation Angle
In the case of orientation studies the measurement of molecular orientation in the crystalline region was carried out by recording the Azimuthal intensity distribution of equatorial plane (100). This was accomplished by fixing the glancing angle 2θ at major peak (100) and rotating the fiber bundle in a plane perpendicular to the direction of the X-ray beam16 The width of the peak at half maximum intensity was calculated to find the crystalline orientation angle.
Crystallite Size The half-width of the crystalline plane (100) was considered for the crystal size calculations from the Scherer’s equation 17. L (hkl) = cos k
(5) where k is constant and a value of 0.9 was considered for our calculations, λ is the wavelength of the radiation used (1.542A0), β is the halfmaximum breadth in radians, and θ is the Bragg’s angle.
RESULTS AND DISCUSSION
The experimental results obtained in the present study are presented and discussed below. Figure 1 shows the XRD patterns of the control, the samples exposed to microwave radiations and heat-set in silicone oil. Order factor, orientation angle and crystal size, calculated on this basis, for parent and drawn polyester (control) samples are given in Table I
The presence of single broad X-ray peak and higher value of orientation angle indicates that the parent sample is amorphous and partially orientated. In case of the drawn sample the lower value of orientation angle with small improvement in order factor could be due to the drawing operation, which was carried out at 85oC slightly above the glass transition temperature. X-ray data for samples exposed to microwave radiations and heat-set in silicone oil for different time intervals are given in Tables II and III respectively. Order Factor The dependence of X-ray order factor on the time of treatment with microwave radiation and silicone oil is given in Table II and III respectively. In both sets of time of treatment. TABLE I. Order Factor, Orientation Angle and Crystal Size calculated from X-ray diffraction for parent and control sample.
Sr. No. Sample X-ray data Order factor/ (Crystalline Index) Orientation Angle (deg.) Crystal Size (A°) 1. PETPOY (Parent) (210) 24.7 - 2. Drawn PETPOY (Control) 0.29 12.1 21.44
FIGURE 1 XRD patterns of polyester fibers, (a) drawn(parent sample), (b) heat-set in s. oil for 15 sec at 180°C ., (c) MW treated for 15 sec., (d) heat-set in s. oil for 60 sec. at 180°C and (e) MW treated for 60 sec. Table II. Order Factor, Orientation Angle and Crystal Size
calculated from X-ray diffraction for PET-POY
control samples exposed to microwave radiations in Glycerol. Sr. No. Time of Treatment (seconds) X-ray data Order Factor Orientation Angle (deg.) Crystal Size (A°)

 1. 15 0.32 12.0 22.61
2 30 0.53 10.5 25.45
3 60 0.64 7.9 40.74
4 90 0.68 7.1 40.74
5. 105 0.71 7.3 37.1
6. 120 0.68 6.0 37.05
It may be noted that the increase in order factor is observed initially for 15 seconds of treatment
compared to the control sample but the increase in the case of silicone oil treatment is higher compared to the microwave treatment. This could be due to the fact that in the case of silicon oil the samples were kept directly at 180°C and microwave treatment was started at room temperature. From the data it is observed that in the case of the microwave treatment there is considerable increase in the order factor observed with time which increased from 0.32 to
0.71 for the time interval of 15 to 90 seconds. In the case of samples heat set in silicone oil there is marginal increase in order factor observed i.e. from 0.45 to 0.52 for the time interval of 15 to 90 seconds. In case of samples exposed to microwaves rapid increase in order factor is observed up to 90 seconds and then it is constant for higher time of exposure. The initial rapid increase may be due to enhancement in primary crystallization by microwave radiations,
which is followed by secondary crystallization. Major structural reorganization is known to take place during primary crystallization, during which crystals grow around nuclei that already exist in drawn PET fiber15.
Crystallite Orientation Angle Data for the effect of microwave radiations on crystallite orientation for different durations of Table III. Order Factor, Orientation Angle and Crystal Size
calculated from X-ray diffraction for PET-POY control samples heat-set in silicone oil at 180°C.
Sr. No. Time of Treatment (seconds) X-ray data Order Factor Orientation Angle (deg.) Crystal (size (A°)
1. 15 0.45 12.4 29.10
2 30 0.48 11.2 30.33
3 60 0.50 11.6 31.33
4 90 0.52 10.3 31.34
5. 120 0.51 12.0 29.00
exposures are presented in Table II and in Table III for heat-setting with silicone oil. A decrease in orientation angle was observed with an increase in time for both sets of samples, which indicates that the crystalline orientation has increased. However, the level of increase in crystalline orientation in the case of samples exposed to microwaves is higher compared to the sample heat-set in silicone oil for the same time interval. The orientation angle decreased from 12.1 to 7.1 when the sample was exposed to microwaves for 90 seconds. While in the case of
silicone oil it is 10.3 for the same time of interval. Crystal Size Crystal size was determined from the (100) plane for both sets of samples. The crystal size increased with an increase in time interval up to 60 seconds and afterwards more or less remained constant for longer time intervals in both cases. V.B. Gupta and et al18 stated that defects in crystals can diffuse out with an increase in heat-setting time, and this lead to a reduction in the crystal width. However, the level of increase in crystal size is also very high in the case of samples exposed to microwave radiations compared to samples heat-set in silicone oil for same time interval. In fact the crystal size of 40.7A° attained by the sample exposed to microwave radiations for 60
seconds is quite high and is beyond expectation.

structure of PET we have carried out a study where the sample was heat set for 60 seconds in the same lossy by using conventional heating. The results compared with the results of the sample exposed to microwave for 60 seconds using the same lossy are given in Table IV.
Table IV. Order Factor, Orientation Angle and Crystal Size calculated from X-ray diffraction for PET-POY control samples exposed to microwave and heat-set in same lossy (Glycerol) by conventional heating for 60 seconds. Sr. No. Time of Treatment (seconds) X-ray data Order Factor Orientation Angle (deg.) Crystal Size (A°) 1. Exposed to Microwaves
0.64 7.9 40.74
2. Conventional heating
0.51 12.0 31.34
It is observed from the Table IV that the order factor, crystalline orientation and crystal size
obtained by the sample exposed to microwaves are very high compared to the sample when heat-set in the same lossy by conventional heating for the same time interval. This shows that the microwave radiations could generate the desired higher crystalline orientation, crystallinity level and crystal size. It therefore appears that microwave radiation in conjuction with lossy material has accelerated action on orienting the molecular chains of polyester. Thus, the potential of microwave radiation in improving the fine structure parameter is clearly observed in this
investigation. However, more study is needed before this treatment can be recommended for industrial use.

AKNOWLEDGEMENT
Thanks are due to Dr. A.N. Desai, Director BTRA for his interest and encouragement. Authors are thankful to Mrs. Archana Konnur, Mrs. Chandrakala and Mr. Mandar Nate for their help through out this work.

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