Identification of polymers by benchmarking

Purpose Of Polymer Benchmarking:

 Purpose of polymer benchmarking varies within the industries or even within the department of an industry. So, purpose of the benchmarking must be clear before we start the activity. Predominantly irrespective of the type of industry, below are the major reasons for which material benchmarking is done.

1) Material selection

2) Quality improvement

3) Cost & Performance Analysis

 

In this blog, we will discuss about the material selection from benchmarking point of view and other topics will be covered in the upcoming blogs.

Material Selection: 

Material selection is a primary role for any practicing polymer engineer. Most of the resources spent in any material R&D is for the right material selection for the intended application.

 Material selection from a benchmarking perspective involves three steps. Material identification, composition analysis and Evaluation & Selection.

Material Identification:

In the material identification stage, below are techniques widely used in the industries.

A) FTIR (Fourier Transform Infrared Spectroscopy):

FTIR is a widely used techniques to identify the type of polymer and primarily it identifies the functional group and chemical bonds within the polymer by absorption of Infrared (IR) light at different wavelengths.Generally FTIR uses mid-Infrared region with the wavelength range of 4000cm⁻¹ to 400 cm⁻¹. 

Identification of polymers from FTIR spectrum alone is very difficult since polymers are compounded materials containing additives with functional group such as plasticizer, antioxidants and fillers  which can interfere and make the spectrum complex. Compared to rubber materials, identifying plastics materials is easier since the spectrum interference is less.Whereas for rubber materials, its very difficult since it is highly compounded. 

Rubber materials

For rubber materials, identification is mostly done based on library comparison. Library comparison from the standard libraries available with most of the FTIR equipments is difficult because standard libraries contains only the spectrum of raw rubbers and not the compounded rubbers.As an Industrial practice, it is recommended to create a library by ourselves by generating spectrum out of known samples. Later, use the generated spectrum for library search. If the library serach doesn't work, may need to go for a pyrolysis process and then go for FTIR analysis.

Thermosetting Resins

In case of thermosetting resins like phenolic, epoxy and polyester resins, identification can be done from the functional group. However the situation is complex in case of materials like polymer composites containing many polymers in the matrix.In such cases,we may need to run the FTIR on the suspected material and then compare with the spectrum of the unknown materials.

Most of the FTIR analysis software contains an interesting feature like comparison of two spectrum and shows the percentage matching, difference,subtraction etc. The features mentioned above can help in identification of thermosetting resins.

FTIR Analysis is quick & Reliable

Though flame tests and wet analysis are available for identification of polymers, FTIR is widely used because of quick analysis and reliable results. It take approximately 2-3 minutes to complete an analysis in FTIR.

B) DSC (Differential scanning Calorimetry)

Identify polymer blends

Though FTIR is widely used for material analysis, in few cases, it very difficult to identify the blends of polymers. In such cases, DSC is an effective technique to where it can show up the thermal transition of the material. For Eg, if two plastic materials are blended, it would show up two peaks with two melting point. 

Other techniques:

Combining the FTIR & DSC analysis, we can identify the polymers present in the system.

Apart from FTIR & DSC, other advanced techniques like GC-MS,NMR Spectroscopy, Raman Spectroscopy are available.However, FTIR & DSC is widely used because of quick analysis, easy sample preparation and less investment compared to other techniques.

Compositional Analysis:

In the compositional analysis, predominantly we try to understand the type of fillers present in the polymer. For example, If we identify an unknown material as PP (Polypropylene) from FTIR analysis, the next question comes to mind is what type of filler used in PP. Is it glass fibre filled or Talc filled? how much percentage of filler used?

Thermo Gravimetry Analyser

To answer the above question, we need to go for a technique called TGA (Thermo Gravimetry Analyser). In this technique, the material is gradually heated until 900 or 1000 deg C in the presence of nitrogen or air and mass loss % with respect to temperature is studied. From the mass loss data,we will be able to identify the fillers in the system and it's percentage.

Identify glass fibre content

If glass fibres in present in the material, it will show up in the residue content, since glass fibre need more temperature to melt or degrade. From the residue content and the fillers content present, we will be able to identify the filler type and percentage.

Glass fibre dimensions:

For the glass filled polymers, it is vital to understand the type of glass fibre from the  length and glass fibre distribution. In such cases, the residue sample from the TGA analysis is taken for analysis by moulding it with a cold set or hot set mold and taken for microscopic analysis. From the microscopic analysis, we can get the dimensions of the glass fibre.

Evaluation & Selection:

More the data, better the decision

It is always difficult to identify a polymer with only one test and more the availability of data, better would be the decision. So, It is always suggested to go for atleast two analysis to conclude. Other than analytical techniques like DSC or TGA, sometimes simple tests like Density, ash content can also provide better information about the material.

Collective decision

In summary, we can identify a material based on benchmarking tests. But when it comes for material selection, it is suggested to take a collective decision by understanding the application conditions, manufacturing feasibility, cost versus benefit analysis, material availability and the regulation compliance.

For more queries on How to select a Rubber for your application? please write to hemapolymercs@gmail.com or comment in this blog.

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How to select a Rubber for your application?

URL: http://polymerscientia.blogspot.com/2023/08/how-to-select-rubber-for-your.html