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Imagine this: you stumbled upon a box of material with no identifiable label or documentation. What do you do? Would you scrap the material or try to identify it? Whether you’re a researcher, material scientist, engineer, student, or a curious individual, identifying an unknown polymer. This blog will guide you through the steps of polymer material characterization.

Advanced Polymer Characterization:

As previously mentioned, there are techniques and methods that can be used to characterize a polymer without the need for advanced analytical equipment. However, the use of analytical equipment can help streamline the characterization process, while providing greater precision and accuracy. As with any type of testing, a material sample is needed. Visually and physically inspecting the sample can be a beneficial step as well. The following will outline some advanced polymer characterization techniques.

• Spectroscopic Analysis: Spectroscopic analysis involves the study of the interaction between matter and electromagnetic radiation which can aid in the identification of the chemical composition and molecular structure of a material.
  
  • Ultraviolet (UV)-Visible Spectroscopy: The basis of this technique is to analyze light absorption or transmission in the ultraviolet (UV) and visible regions of the electromagnetic spectrum. This method aids in the identification of chemical compounds and their concentration in a solution.
    
    
  • Infrared (IR) Spectroscopy: IR Spectroscopy studies how a sample interacts with infrared light through absorption, emission, or reflection of the IR light. This analysis provides information about molecular vibrations, which in turn help to identify functional groups in organic compounds, aid in determining molecular structure, and help to analyze chemical bonding.

Figure 2. FTIR of PA 6 [1]

• Thermal Analysis: Analytical techniques are used to study how the physical and chemical properties change as a function of temperature. Some common techniques used in thermal analysis are the TGA and DSC.
  
  • Thermogravimentric Analysis (TGA): TGA quantifies the mass change of a sample as it experiences heating or cooling at a constant rate, allowing the test to identify thermal degradation, decomposition, and the detection of volatile components in the material.

Figure 3. TGA of PA 6,10 [1]

• Chromatographic Analysis: Polymer chromatographic analysis refers to the use of chromatographic techniques to separate, identify, and quantify polymers. Chromatography is a versatile analytical method that enables the separation of complex mixtures through interactions with a stationary and a mobile phase. This type of analysis can be used to determine a polymer's composition, molecular weight distribution, structural traits, monitor polymerization processes, and assess polymer purity. Two common chromatographic analysis methods are GPC/SEC and HPLC.
  
  • Gel Permeation Chromatography (GPC) or Size Exclusion Chromatography (SEC) differentiates polymers by their molecular size, particularly their hydrodynamic volume or molecular weight. In this method, larger polymer molecules have reduced penetration into the porous stationary phase. This leads to distinct retention times and facilitates the separation based on the molecular size.

Figure 5. How GPC/SEC separates molecules of different sizes [4]

• High Performance Liquid Chromatography (involves dissolving a polymer sable and subjecting it to a high-pressure liquid mobile phase and a stationary phase creating separation. HPLC is more common for analyzing low molecular materials, additives, and oligomers.

• Microscopy: Microscopy can help study polymer, and behavior at the microscopic level via physical observation. This allows insight into polymer properties, crystallinity, and the of additives within a polymer matrix. The distribution of an additive would show the uniformity of the additive in the polymer and the concentration would show the volume of additive versus polymer. Some common microscopy methods are as follows:
  
  • Optical Microscopy: Optical Microscopy is a common technique to observe samples under visible light. This method enables the observation of surface topography, phase morphology, and material defects. A modified approach to this method would involve polarized light, which can aid in identifying birefringent regions in the material to reveal molecular orientation and stress-induced effects.
    
    
  • Scanning Electron Microscopy (SEM): SEM utilizes a focused electron beam to scan the surface of a sample. This then generates high-resolution images of the polymer surfaces, which can unveil crucial details about surface topography, porosity, and the presence of fillers or additives.

Figure 6. SEM vs. TEM of Silicon [5]

• Transmission Electron Microscopy (TEM): TEM is a powerful technique used to study polymer samples at the nanometer scale. This technique transmits electrons through thin sections of a material, which then provides a detailed analysis of crystalline structures, phase separation, and morphology.

Table 2. SEM vs. TEM [6]

SEM	TEM
Focused beam	Broad beam
Topographical/surface (3D image)	Internal structure (2D image)
Beam does not penetrate sample	Beam does penetrate sample
Faster test, less expensive	Slower test, more expensive

• Mechanical Testing: Mechanical property testing offers valuable information on how polymers handle forces, stresses, and strains, which can then provide insight into a material’s suitability for polymer applications. Some standard mechanical testing methods under the American Society for Testing Materials (ASTM) are as follows:
  
  • Tensile testing (ASTM D638): Tensile testing subjects a material to an axial pulling force along its longitudinal axis until it breaks. The goal of tensile testing is to determine the (area under stress-strain curve up to the point of fracture). Testing is typically done on a machine like the Instron Universal Testing Machine. Tensile testing can help identify how a material will behave under tension offering clues to its composition. Stress-strain data generated during this test is unique to each material tested and can lead to information about the mechanical properties. The slope of the initial linear region (elastic region) of the stress-strain curve provides the elastic modulus which is indictive of the material’s stiffness. Polymer materials have distinct elastic moduli, making this parameter a useful differentiator.

Figure 7. Typical Stress-Strain Curve of a Thermoplastic Material [7]

• Flexural Testing (ASTM D790): Flexural testing, or bending testing, is done when perpendicular force is applied to a sample's longitudinal axis causing it to bend. The goal of this testing is to determine, which is typically done on a machine like the Instron Universal Testing Machine. Flexural strength is the maximum stress a material can withstand before it fails when subjected to a bending load. With polymers having distinct flexural strengths, this can be indicative of a material’s structural integrity and stiffness. Like the flexural strength, the flexural modulus (modulus of elasticity in bending) is the measure of a stiffness when subjected to bending. This test can provide information about the polymer’s rigidity and testing values can be equated to those found on a technical datasheet

Figure 8. Instron Universal Testing Machine [8]

• Impact Testing (ASTM D256 Izod Impact/ASTM D6110 Charpy Impact): Impact testing assesses a material’s ability to withstand sudden and dynamic loading like impact or shock forces. The goal of impact testing is to determine. The impact strength the measure of the material’s ability to resist cracking or deformation under impact or sudden shock loads, whereas the fracture toughness is related to crack propagation. The Izod and Charpy tests are similar, however, the Charpy test uses a cantilever beam to strike a specimen at a notched location whereas the Izod test uses the cantilever beam to strike the side of the specimen opposite of the notch. The Izod/Charpy impact testing is conducted on a Pendulum-style test machine. Polymers will undergo either brittle or ductile fractures, which are related to their molecular structure and toughness and understanding these mechanics can aid in the material identification

Figure 9. Pendulum Impact Test Machines [9]

• Rheological Analysis: Rheological analysis, or rheology, explores how materials flow and deform under the influence of applied forces. Rheology testing is key to understanding a material’s viscosity.

Figure 10. Dynisco LCR7000 Series Capillary Rheometer [10]

Conclusion:

The process of identifying an unknown polymer can either involve a few basic testing techniques or intricate analytical methods. Identifying an unknown polymer can unlock the potential for innovation and the development of novel applications. The simplistic testing procedures and advanced analytical methods can be tedious and should be reviewed with a polymer expert. Don’t hesitate to reach out to your local Nexeo Technical Team for questions regarding polymer material testing.

View what Technical Solutions Nexeo Plastics can provide you here.

[1] Vahur, Signe, et al. “ATR-Ft-IR Spectral Collection of Conservation Materials in the Extended Region of 4000-80 Cm–1 - Analytical and Bioanalytical Chemistry.” SpringerLink, Springer Berlin Heidelberg, 11 Mar. 2016, link.springer.com/article/10.1007/s00216-016-9411-5.

[2] Spurrell, Timothy. Timothy Spurrell, Billerica, MA, 2016, pp. 7–7, Experiment II - TGA & UL94HB Testing.

[3] Spurrell, Timothy. Timothy Spurrell, Billerica, MA, 2016, pp. 5–5, Experiment III - DSC & Melt Point Testing.

[4] An Introduction to Gel Permeation Chromatography and Size Exclusion Chromatography, 30 Apr. 2015, www.agilent.com/cs/library/primers/Public/5990-6969EN%20GPC%20SEC%20Chrom%20Guide.pdf.

[5] “Transmission Electron Microscopy vs Scanning Electron Microscopy.” Electron Microscopy | TEM vs SEM | Thermo Fisher Scientific - US, www.thermofisher.com/us/en/home/materials-science/learning-center/applications/sem-tem-difference.html#:~:text=The%20difference%20between%20SEM%20and,sample)%20to%20create%20an%20image. Accessed 10 Oct. 2023.

[6] Gleichmann, Nicole. “SEM Vs TEM.” Analysis & Separations from Technology Networks, 4 Sept. 2023, www.technologynetworks.com/analysis/articles/sem-vs-tem-331262.

[7] Campo, E. Alfredo. (2006). Complete Part Design Handbook - For Injection Molding of Thermoplastics - 2.2.1 Stress-Strain Behavior. (pp. 7). Hanser Publishers. Retrieved from

https://app.knovel.com/hotlink/pdf/id:kt004X3IB1/complete-part-design/stress-strain-behavior

[8] “Universal Testing System | Instron.” UNIVERSAL TESTING SYSTEMS, www.instron.com/en-us/products/testing-systems/universal-testing-systems/low-force-universal-testing-systems/6800-series. Accessed 10 Oct. 2023.

[9] “Impact Testing Systems | Instron.” IMPACT TESTING SYSTEMS, www.instron.com/en-us/products/testing-systems/impact-systems. Accessed 10 Oct. 2023.

[10] “Capillary Rheometers: Material Characterization Equipment.” Capillary Rheometers | Material Characterization Equipment, www.dynisco.com/polymer-evaluation/laboratory-quality-control-testing/capillary-rheometers/lcr7000-series. Accessed 10 Oct. 2023.