8/29/13 Page 1 | 11/12/13 Thermal Analysis Unlocks the Secrets of Elastomers Brian Bacher, Technical Specialist, NSL Analytical Services, Cleveland, Ohio Michael Walker, Chemist, NSL Analytical Services, Cleveland, Ohio Alan Riga, Adjunct Professor, Case Western Reserve University, Cleveland, Ohio Elastomer technology is as much an art as a science. And the constituents of a particular elastomer are often closely held secrets. This situation often puts an end user in a difficult situation. If a particular material is the only one that fits a need, the user is at the mercy of the compounder from a cost and supply standpoint. Elastomers can contain dozens of components at varying concentrations, including polymers, plasticizers, fillers, and stabilizers. Lubricants, antioxidants, flame retardants, and other components can also be present. To help identify the components in an elastomer, a reliable technique to help reverse engineer a material would be a welcome addition to an analyst’s arsenal. Such a method would begin to enable a user to determine the components in a material and seek a second, perhaps less costly, source. Reverse engineering also allows companies to duplicate or improve on a specific formulation. In addition, it provides the knowledge needed to understand the nature of the various components of a formulation, the ingredient concentration and how the components and ingredients interact. TGA to the Rescue An analytical technique based on Thermal Gravimetric Analysis (TGA) has been developed to determine the constituents of thermoplastic polymers. The analysis has many uses, including: • Characterizing competitive products • Identifying batch to batch variations • Comparative analysis of good and bad samples • Investigating possible patent or trade secret infringement
Transcript
8/29/13
Page 1 | 11/12/13
Thermal Analysis Unlocks the Secrets of Elastomers Brian Bacher, Technical Specialist, NSL Analytical Services, Cleveland, Ohio
Michael Walker, Chemist, NSL Analytical Services, Cleveland, Ohio
Alan Riga, Adjunct Professor, Case Western Reserve University, Cleveland, Ohio
Elastomer technology is as much an art as a science. And the constituents of a
particular elastomer are often closely held secrets. This situation often puts an end
user in a difficult situation. If a particular material is the only one that fits a need, the
user is at the mercy of the compounder from a cost and supply standpoint.
Elastomers can contain dozens of components at varying concentrations,
including polymers, plasticizers, fillers, and stabilizers. Lubricants, antioxidants,
flame retardants, and other components can also be present.
To help identify the components in an elastomer, a reliable technique to help
reverse engineer a material would be a welcome addition to an analyst’s arsenal.
Such a method would begin to enable a user to determine the components in a
material and seek a second, perhaps less costly, source.
Reverse engineering also allows companies to duplicate or improve on a specific
formulation. In addition, it provides the knowledge needed to understand the nature
of the various components of a formulation, the ingredient concentration and how
the components and ingredients interact.
TGA to the Rescue An analytical technique based on Thermal Gravimetric Analysis (TGA) has been
developed to determine the constituents of thermoplastic polymers. The analysis has
many uses, including:
• Characterizing competitive products
• Identifying batch to batch variations
• Comparative analysis of good and bad samples
• Investigating possible patent or trade secret infringement
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TGA measures the change in weight of a material as a function of temperature or
time in a specific atmosphere (typically nitrogen or air). These measurements are
used to determine the composition of materials and predict their thermal stability
(temperature of weight loss or gain).
TGA can determine the thermal and oxidative stability of materials, the
composition of multicomponent systems, the moisture content and dehydration, and
the decomposition kinetics of materials. In a typical analysis, a 20 mg sample of the
material is heated to 600°C in nitrogen then switched to an oxygen atmosphere (for
carbon black) up to 850°C. Mass loss is measured at appropriate temperatures as
indicated by the first derivative of the TGA curve.
TGA Analysis of Typical Polymers
Source: Reference 1
TGA Analysis shows the thermal stability of thermoplastic polymers. PVC is the least stable, and polyimide is the most stable.
TGA can be augmented with Differential Scanning Calorimetry (DSC), which
measures the difference in heat flow rate between a sample and a reference as both
are heated, cooled or held isothermal. This technique provides a great deal of
information about the material, as shown in the table below.
Applications of DSC
Property Ther
mop
last
ic
Ther
mos
et
Elas
tom
er
Che
mic
als/
D
rugs
Petr
oleu
m
Gla
ss
Met
al
Prot
eins
/ St
arch
es
Glass Transition Temperature (Tg) X X X X X X X X Glass Transition Size (ΔCp) X X X X X X Melting Temperature (Tm) X X X X X X X Crystallization Temperature (Tc) X X X X X X Crystallinity (J/g not %) X X X X X X Heat Capacity (J/g-°C) X X Oxidative Stability (Temp or Time) X X Texturing (process) Temperature (°C) X Curing/Degree of Cure (%) X X Polymorphic Transitions X Denaturation/Gelatinization X
Source: Reference 1
Differences in heat flow occur due to the heat capacity of the sample, which
increases with temperature, and at various transitions that occur in the sample as
shown in the figure below. Heat flow rate can be expressed in a variety of units that
can also be normalized for the weight of sample used.
Some Possible Transitions in a DSC Curve
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Source: Reference 2
Plot of heat flow vs. temperature shows exothermic and endothermic transitions in the material. Exothermic transitions such as crystallization, curing and oxidation
release heat. Endothermic transitions such as melting, glass transition and evaporation absorb heat. Decomposition can be either endothermic or exothermic.
The following ASTM methods can be used in conducting a thermal analysis of an
elastomeric part:
• ASTM D297 Standard Test Methods for Rubber Products Chemical Analysis
• ASTM D6370 Standard Test Method For Rubber - Compositional Analysis By
Thermogravimetry
• ASTM E1131 Standard Test Method for Compositional Analysis by
Thermogravimetry
• ASTM D3418 Standard Test Method for Transition Temperatures and
Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning
Calorimetry
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An Example Analysis Rubber materials from two different suppliers were analyzed with TGA to
determine their composition. Results of the analysis are shown in the plots below.
