Epoxy dynamic mechanical properties

Wilson, W.T. "Effect of Radiation on the Dynamic Mechanical Properties of Epoxy Resins and Graphite Fiber/Epoxy Composites", 1986, Ph.D. Thesis, North Carolina State University, Raleigh, NC. 

Ozonization of lignin forms derivatives of muconic acid that have the unique chemical structure of conjugated double bonds with two carboxyl groups. These derivatives have great potential for chemical modification. The ozonized lignin of white birch was soluble in epoxy resin at 120°C, and the free carboxyl groups were found to react with epoxide. This paper discusses developmental work on the preparation of pre-reacted ozonized lignin/epoxy resins the dynamic mechanical properties of cured resins and preliminary results of the application of these resins as wood adhesives. 

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical properties of the sol-gel-derived acrylic rubber (ACM)/silica, epoxi-dized natural rubber (ENR)/silica, and polyvinyl alcohol (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay et al. [27]. Theoretical delineation of the reinforcing mechanism of polymer-layered silicate nanocomposites has been attempted by some authors while studying the micromechanics of the intercalated or exfoliated PNCs [28-31]. Wu et al. [32] verified the modulus reinforcement of rubber/clay nanocomposites using composite theories based on Guth, Halpin-Tsai, and the modified Halpin-Tsai equations. On introduction of a modulus reduction factor (MRF) for the platelet-like fillers, the predicted moduli were found to be closer to the experimental measurements. 

The dynamic mechanical properties of the siloxane-modified epoxy networks were also investigated. The DMTA curves for the control epoxy network exhibit the two major relaxations observed in most epoxy polymers 39 40,41>. A high temperature or a transition at 150 °C corresponds to the major glass transition temperature of the network above which large chain motion takes place. The low temperature or (5 transition is a broad peak extending from —90° to 0 °C with a center near —40 °C. It has been attributed predominantly to the motion of the CH2—CH(OH)—CH2—O (hydroxyether) group of the epoxy 39-40 2 ... 

Many different methods can be used to measure the degree of crosslinking within an epoxy specimen. These methods include chemical analysis and infrared and near infrared spectroscopy. They measure the extent to which the epoxy groups are consumed. Other methods are based on the measurements of properties that are directly or indirectly related to the extent and nature of crosslinks. These properties are the heat distortion temperature, glass transition temperature, hardness, electrical resistivity, degree of solvent swelling and dynamic mechanical properties, and thermal expansion rate. The methods of measurement are described in Chap. 20. 

Structures and Dynamic Mechanical Properties of Epoxy Resins Cured... 

A number of papers deals with the dynamic mechanical properties of cured epoxy resins1 -5) and with the effect of the structure of basic resins and the degree of cross-linking s 8>. 

In this review, the effect of the cured epoxy resins on the dynamic mechanical properties of epoxy resins is discussed. 

The mechanical properties and dynamic mechanical properties of the cured epoxy resins are governed by their structures. 

Table 3. Dynamic mechanical properties and flexural strength of diamine cured epoxy resins...

Table 6. Dynamic mechanical properties for epoxy resin cured with acid anhydrides...

The dynamic mechanical properties of three epoxy resins cured with diphenyl-methane diisocyanate (MDI) are shown in Fig. 15. Since these resins consist of many bulky cyclic structures, Tg (a-dispersion) is above 200 °C and the transition region is wide. In the DEN 431 —L-MDI resin, Tg is higher than 300 °C. The resin is expected to be highly heat-resistant51). 

Fig. 19. Dynamic mechanical properties as a function of epoxy curatives65 . Hardener 1 PMDA, 2 HHPA, 3 MPDA, 4 DETA, 5 DMP-30...

On the other hand, many studies on dynamic mechanical properties at temperatures lower than room temperatures have been reported 5,7 63,64). For example, a small (3 transition near —50 °C has also been observed in epoxy resins. Cuddihy 65,661 observed a (3 transition in resins cuted with different hardeners such as DETA, MPDA, HHPA, pyromellitic dianhydride (PMDA), and tris(dimethylaminomethyl)-phenol (DMP-30) (Fig. 19). The larger the size of the P transition, the higher the impact strength (Table 8). 

If a rubber-like polymer is used as the vinyl polymer, this IPN will show good damping properties at elevated temperatures. So, butyl acrylate, ethylene glycol dimethacrylate, phenolic novolac, and bisphenol A type epoxies were used as IPN components. The dynamic mechanical properties of these IPNs were examined first, because the loss tangent is very important to damping properties. Then the damping properties of IPN and commercial chloroprene rubber were measured at various temperatures. 

These results lead to the conclusion that the parameter most effective in controlling the loss tangent and Tg is the equivalent ratio of epoxy to phenolic. In this system, phenolic components mainly determine the dynamic mechanical properties rather than acrylates. 

Dynamic mechanical properties are used In this work to develop an understanding of how epoxy based networks respond to different hygrothermal environments. A fundamental understanding of why property changes occur as a result of hygrothermal exposure Is provided. 

Numerous efforts have focused upon the nature of moisture transport of epoxy systems. Previous-sorption desorption work demonstrated that equilibrium moisture levels In an epoxy system can be related to thermodynamic states (1,2,3). Transient and equilibrium dynamic mechanical experiments are performed In this work with two epoxy systems TGEBA-TETA and N-5208. These experiments provide Insight Into the nature and extent that network changes have on the dynamic mechanical properties as a result of hygrothermal cycling. 

Epoxy film samples were prepared with the DGEBA-TETA and N-5208 resins. Detailed Information on the DGEBA-TETA and N-5208 resin cure and sample preparation has been previously provided (2,4). Films of the N-5208 resin were made with a curing agent concentration of 25 PHR-DDS (4) 14 PHR TETA was used for curing the DGEBA epoxy (2). Dynamic mechanical properties for films were measured on strip samples cut to nominal 0.02 cm x 0.3 cm x 6.0 cm dimensions. 

Two different types of dynamic mechanical experiments were performed. First, the temperature dependence of "equilibrium" dynamic mechanical properties for all epoxy samples were obtained... 

Equilibrium Dynamic Mechanical Data. Dynamic mechanical properties of both the DGEBA-TETA and the N-5208 epoxy systems exhibit characteristic transitions observed in many polymeric materials. Figures 2a and 2b Illustrate "equilibrium" dynamic mechanical tan 6 as a function of temperature for samples saturated at different moisture levels. 

A convenient way to quantify the Increase In magnitude of the u transition with the Increase In epoxy moisture content Is to compare the area under this transition peak with sample moisture content. Several possible dynamic mechanical property comparisons exist. No Identifiable trends were observed between the magnitude or area of the loss modulus (E") or tan d and the amount of moisture In the N-5208 or DGEBA-TETA epoxy samples. 

There are two basic types of transient dynamic mechanical experiments which were performed In this study. The first type Involves Isothermal cycling of an epoxy sample between a dry and wet environment. The second type of experiment Involves cycling the epoxy sample between two different temperatures under a liquid water environment. In each case, the transient and equilibrium values of dynamic mechanical properties change In a unique manner. 

Tan 5, storage compliance, and loss compliance values for these experiments are plotted as a function of time in Figure 8. This transient temperature cycle data illustrates interactions between the dynamic mechanical plasticization and blocking behavior just discussed as well as the epoxy s equilibrium moisture uptake behavior (3), and the temperature behavior of dynamic mechanical properties observed for this epoxy in Figure 2a. Perhaps the easiest comparison to consider involves the relationship between transient temperature cycling data of Figure 8 and the thermal behavior observed for N-5208 epoxy tan 6 data of Figure 2a. 

Figure 8. Transient dynamic mechanical properties of 25 PHR-DDS N-5208 epoxy sample during liquid water thermal cycling between 20 C and 50 C.

J. D. Keenan, J. C. Seferis, and J, T. Quinlivan, J.A.P.S., 24, 2375, (1979) J. D. Keenan, Structure and Dynamic Mechanical Properties of TGDDM-DDS Epoxy, Graphite Fibers and Their Composites, M. S. Thesis, Department of Chemical Engineering, University of Washington, Seattle, Washington (1979). 

Mijovic, J. Tsay, L.L. Correlations between dynamic mechanical properties and nodular morphology of cured epoxy resins. Polymer... 

Table IV. Dynamic Mechanical Properties of Series E and Series F Epoxy Networks...

Pierre et al [173] considered the effects of crosslink density on dynamic mechanical properties and plastic deformation of epoxy-amine networks, varying chain stiffness by using... 

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