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Use of DLTMA Techniques to Determine Glass Transition

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Use of DLTMA Techniques to Determine Glass Transition Temperature of Highly Cross Linked Thermoset Composites

 

This paper describes the investigation of Differential Load Thermo Mechanical Analysis (DLTMA) techniques to determine the glass transition temperature (Tg) of glass fiber reinforced thermoset composites.  Traditional TMA techniques rely upon detection of the discontinuity of α (Coefficient of Thermal Expansion) with respect to temperature to determine Tg.  Although widely used, the traditional TMA technique has limitations in detection of Tg of structural composites.  This is because structural composites have a high percentage of reinforcement (upwards of 50% by volume) which mutes or distorts the signal.The DLTMA technique relies on the stress-strain analysis of the composite to determine Tg. An oscillating force is applied by the TMA and the resulting deflection is measured.  For highly cross linked thermoset polymers, the stress-strain response is elastic in nature. Hence Hooke’s law of (Modulus = stress/strain) would apply. Therefore as the polymer goes through a glass transition, its modulus would drop and its response to the applied constant oscillatory stress would change. Two types of pultruded composites, with two different resin matrices were tested. Samples of approximately 5mm x 15mm x 1.5mm thickness were taken from the pultrusions for analysis. The first composite designated as XP, had dimensions of 0.25in (6.35 mm) x .625in (15.89 mm), and had an Epoxy + Anhydride polymer matrix. The second composite designated as H9, had dimensions of 1.50in (38 mm) x 0.49in (12.45 mm) and used a urethane acrylate type polymer matrix. This thermal analysis study provides Tg comparisons obtained by TMA, DLTMA, and DMA. The samples subjected to the DLTMA technique had Tgs that corresponded to onset Tgs determined via DMA (Dynamic Mechanical Analysis). The study demonstrated that the Tg was easily detected with the DLTMA technique when analyzing the Deflection vs Temperature graph generated by the TMA and is superior to a standard TMA in resolution when analyzing structural composites.

 

Author: Fayaz Ali

 

Conference: SAMPE Seattle 2017

 

SKU/Code: SE17--0865

Pages: 17

 


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