·Table of Contents
·Materials Characterization and testing
Novel NDE Application of Vibrational Spectroscopy: A Tool for Offline and Online Evaluation of Physico-mechanical Properties of Polymer Based MaterialsDr.GIRISH C.PANDEY
Senior Manager (R&D)
Dr.AJAY KUMAR, RAJENDRA GARG
Indian Petrochemicals Corporation Ltd.
Baroda 391346, Gujarat, India
e mail : email@example.com
Samples (both Polybutadiene Rubber -PBR and that of Polypropylene Copolymer- PPCP) produced in a commercial plant over a period of time were used in the present study. Two grades of PPCP samples ( grade A having low MFI and grade B with high MFI ) were studied both by the present method and also by the currently accepted ASTM methods for the quality control / quality assurance (QC / QA) purpose .
IR spectra of films ( PBR films were prepared by casting the it over NaCl window from its benzene solution and that of the PPCP were prepared by thermal casting) were recorded in transmission mode using Bruker IFS-113V FTIR spectrometer modified to incorporate the spectral range 1000-10000 cm-1. The spectral accumulation was done at a resolution of 8 cm-1with mirror velocity at 3 cm/seconds, zero filing factor of 2 and 4P apodization. All measurements were made under vacuum .The spectral averaging was done with 64 scans. The spectra were plotted in absorbance mode and absorbance was used for the evaluation of different properties of these polymers.
C. Data Analysis:
Quantitative spectral analysis for the determination of various physical /mechanical parameters was carried out using an in-built multivariate statistical program. The chemometric algorithm software performs factor analysis followed by the data regression on the spectrum in the predetermined region and is used to obtain the desired properties in case of PPCP and a simple direct regression equation was developed for the evaluation of Tensile strength in case of PBR.
D. Mechanical Properties:
I.Measurement of diffrent properties of PPCP Samples:
The ASTM (No:D-1238, D-256, D-790) methods were used for the measurements of mechanical properties viz av. MFI, Izod Impact and Flexural Modulus respectively [4,5].
II. Measurement of Tensile strength [Ts (std)] by standard reference method for PBR:
The measurement of tensile strength of rubber sample is a multistep and time taking method. The test method followed in the present work conformed to ASTM. The representative rubber sample was mixed with several additives, the recipe of which is given elsewhere[6,7]. All the contents were weighed accurately and mixed thoroughly in a BR Type Banbury mixer at a temperature of 50 ± 5°C. The blended rubber was passed three times through the 6 inch rolls at roll gap of 5 mm. Vulcanize the sample for 35 minutes at 145°C and place the vulcanized rubber into water for 10-15 minutes: The vulcanized rubber was left for 72 hours (curing). The standard test samples for tensile testing were prepared and tensile strength Ts (std) was measured by a universal testing machine.
1. Evaluation Of Various Properties:
Being hydrocarbon based materials, the IR spectra of the samples recorded in the range 1000-4000 cm-1 showed typical absorption bands at j 2900 cm-1( CH stretching ) , 1460-1165 cm-1( CH bending and C-C stretching) . Some of these spectral features have been used for the determination of various properties ( eg av. MFI, izod impact and flexural modulus of PPCP and Tensile Strength of PBR samples).
The simulation studies were done using a set of training samples of known properties as reference . The calibration was done using an on line chemometric algorithm by assigning a particular wavelength range. The descrete wavelength region used for the prediction of all three parameters from the spectra, was identified based on the combination of theoretical consideration and finer improvement by trial and error method. A distinct correlation between absorbance and the property of interest was established initially on training data which , then , was extended to unknown samples.
In order to establish the validity of the method , the reproducibility and reliability of data was checked. Multiple recording and analysis of the spectral data on one of the samples was carried out and various properties viz. av. MFI, izod impact and flexural modulus in case of PPCP and Tensile Strength in case PBR, were determined by the present method .Statistically excellent reproducibility of the data has been obtained.
4. Determination of physico-Mechanical Properties:
Conventionally infra-red spectroscopy has extensively been used to understand / derive structural information about a sample, this was later extended to get quantitative information about the functionalities present in a matrix or the sample . In view of the fact that various chemical and physico-mechanical properties of sample are basically dependent upon their composition and structure. It is, therefore, quite reasonable to conclude that any information related to above at microscopic level can be used to predict the various macro properties . In the light of above , we have attempted to develop a novel correlation between the micro-structural features of the sample with its macrolevel physico-mechanicalproperties. Based on this hypothesis, we have undertaken a study on a few systems and used the structural features represented by their IR spectrum to predict their (physico-mechanical) properties.
Various properties viz., av. MFI, izod impact and flexural modulus of two different grades of PPCP have been determined using IR spectral data [4,5]. A careful analysis of various spectral features based on theoretical considerations have been used to identify a spectral range (representing the contribution from CH bending and C-C stretching , arising from both ethylene & propylene moities of the copolymer) , which , in turn , was used to predict the various properties mentioned above using an inbuilt multivariate chemometric algorithm. The details of the method are described below.
For each grades of PPCP the calibration and analysis were carried out separately. The results of analysis have been tabulated in Tables-1A &1B for low and high MFI PPCP
|SR.NO||AV.MFI||IZODIMPACT KG. CM/ CM||FLEXURALMODULUS KG/SQ.CM|
|Table 1-A: Physicomechanical Properties of PPCP determined by IR and ASTM methods Sample(Grade-A: Low MFI)|
|SR.NO||AV.MFI||IZODIMPACT KG. CM/ CM||FLEXURALMODULUS KG/SQ.CM|
|Table 1-B: Physicomechanical Properties of PPCP determined by IR and ASTM methods Samples(Grade-B: High MFI)|
For comparison the results of ASTM methods are also given . The results of IR based method showed an excellent match with those determined by ASTM method. For more critical comparison, the various statistical parameters like % deviation, standard deviation etc. were also calculated for IR and ASTM data and found to be in good agreement . A comparison of actual values showed again an excellent agreement between IR and ASTM the two methods.
The PBR system was chosen specifically to demonstrate that a very complicated (involving multistep processes like mixing of additives, curing , molding etc.) and time taking method ( generally used for quality control/ assurance ( QC/QA) purpose ) can be replaced by a fast , simple and direct measurement method i.e. recording of infra-red (IR) spectrum of PBR film (made from its solution) and determination of absorbance ratio of pre-selected bands [6,7]. We have tested the method on a large number of the samples produced over a period of time (more than 6 months ).
Based on preliminary data ( used as reference or training data) a simple linear relationship (equation ) between response (Ts) and input (X = absorbance ratio)
parameters has been developed. Using this relationship , the variation performance was minimised.This, thus, avoids the requirement of standard reference samples for calibration i.e. the spectral data directly can be fed into the equation to obtain the tensile strength (Ts )
|Ts = 7.9836 X + 3.564 --------- (1)|
where X = absorbance ratio
The estimated tensile strength Ts (IR) from equation-1 is given in Table-2 along with the absorbance ratio and Ts (std) values determined by the standard method. An excellent agreement between the Ts (std) values and that Ts (IR) has been found. The reproducibility of the method was established by multiple spectral recording and analysis of the same sample . It may not be out of place to mention that statistically the measurement data on 40 samples showed very good comparison between Ts (IR) and Ts (std) (Table-2).
|Table 2: Tensile strength of PBR|
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