Aging nanocomposites

Presence of nanosilica and its interaction with the rubber matrices strongly affect the low and high temperature degradation behaviour of the hybrid nanocomposites. Figure 3.24 shows the post-aging swelling analysis of the cross-linked ACM-sihca and ENR-silica hybrid nanocomposites. The data points are collected after aging of the samples at 50°C, 70°C, and 90°C for 72 h. 

FIGURE 3.24 Plots of volume fraction of the filled rubber in the swollen gel (Vrf) against aging temperature for acrylic rubber (ACM)-silica and epoxidized natural rubber (ENR)-silica hybrid nanocomposites. (From Bandyopadhyay, A. and Bhowmick, A.K., Plastic Rubber Comp. Macromol. Eng., 35, 210, 2006. Courtesy of Money Publishers.)... 

Figure 7.6 Young s moduli of the GPTMS-boehmite nanocomposite and the hybrid gel derived from GPTMS-A1(OBu)3 aqueous solution. Samples without ageing were dried at 50 °C for 16 h and then at 110°C for 16 h. The aged samples were dried at room temperature for 9 days before being dried at elevated temperatures (50 °C for 16 h and then 110°C for 16h). (Reproduced from ref. 5, with permission.)...

Ptd-L solution (solvent - water for injections) prepared for Platidiam adsorption onto magnetically sensitive nanocomposites (C = 1 mg/1). The age of Ptd-L solution before the experiment was 14 hours ... 

Degradative Thermal Analysis and Dielectric Spectroscopy Studies of Aging in Polysiloxane Nanocomposites... 

The characterization of the physical and chemical changes that occur in montmorillonite/PDMS nanocomposite elastomers as they are thermally aged is reported. Broadband Dielectric Spectroscopy (BDS) was used to track changes in the physical interaction between the polymer and clay associated with increases in non-oxidative thermal stability (as determined by TGA). The evolution of volatile siloxane species from the elastomers was characterized with Thermal Volatilization Analysis (TVA). Results suggest that the improved thermal stability and the increases in polymer/clay association are a result of significant re-structuring of the polymer network. 

The aging behavior of conventional filled polysiloxane materials has been relatively well studied. However, there is little currently known about the long term stability and aging behavior of polysiloxane nanocomposites. This is a key issue that must be addressed if polysiloxane nanocomposites are to become part of the next generation of polymeric materials. 

TGA was utilized to monitor the non-oxidative degradation behavior of the nanocomposite systems as a function of age time. Onset temperatures for non-oxidative degradation were determined from the first derivative of the sample mass. Figures 6 and 7 illustrate the trends in non-oxidative degradation temperature with age time for all systems under both environments. 

It is reasonable to link the mass loss with the observed changes in thermal stability and dielectric response, indeed some of this material that is evolved from the systems on aging is likely to be water and the reaction residues implicated as pro-degradants. However, the level of material lost the ongoing nature of the process and the clear link once again with a moist air environment points to an explanation other than simple passive loss of volatile residues from the nanocomposites. Cleary, an identification of this volatile material is desirable if the nature of the aging processes occurring within these polysiloxane nanocomposites is to be elucidated. 

TVA was employed in order to characterize the volatile species that were evolved from the nanocomposite systems on aging. The goal of the study was... 

This strongly suggests that these cyclic oligomeric siloxanes are being actively produced within the nanocomposite systems as a result of the thermal aging and are not simply passive residues from the initial synthesis. 

S.K. Young, W.L. Jarrett, and K.A. Mauritz. Studies of the aging of Nafion (R)/sihcate nanocomposites using Si-29 sohd state NMR spectroscopy. Polymer Engineering and Science 41, 1529-1539 2001. 

PbS/polyacrylonitrile nanocomposite which consists of quasi-spherical PbS particles of 8nm in diameter, homogeneously dispersed and well separated in the polymer matrix. The polyacrylonitrile was chosen, being a good heat-insulator and an aging-resistive material. To provide an homogeneous system, in which the reactants are well mixed at the molecular lever, and to ensure the presence of solvated electrons, absolute ethanol was used as solvent [2] ... 

This chapter reports the results of the literature that concerns the photooxidation of polymer nanocomposites. The published studies concern various polymers (PP, epoxy, ethylene-propylene-diene monomer (EPDM), PS, and so on) and different nanofillers such as organomontmorillonite or layered double hydroxides (LDH) were investigated. It is worthy to note that a specific attention was given to the interactions with various kinds of stabilizers and their efficiency to protect the polymer. One of the main objectives was to understand the influence of the nanofiller on the oxidation mechanism of the polymer and on the ageing of the nanocomposite material. Depending on the types of nanocomposite that were studied, the influence of several parameters such as morphology, processing conditions, and nature of the nanofiller was examined. 

Recently, La Mantia et al reported a study of LLDPE/clay nanocomposites with appropriate additives [103], The photochemical behavior of nanocomposites without and with different UV stabilizers was studied under artificial accelerated conditions of ageing. Addition of a metal deactivator to the LLDPE-clay nanocomposites was also compared. Stabilizing effect on the physical properties such as elongation at break and tensile strength were described. The most effective photostabilization of these LLDPE/clay nanocomposites was achieved in presence of the metal deactivator. 

Planes, E., Chazeau, L., Vigier, G., and T. Stuhldreier. 2010. Influence of sihca fillers on the ageing by gamma radiation of EDPM nanocomposites. Composites Science and Technology 70 1530-1536. 

Priestley, R. D., Rittigstein, P., Broadbelt, L. J., Fukao, K., and Torkelson, J. M., Evidence for the molecnlar-scale origin of the snppression of physical ageing in confined polymer fluorescence and dielectric spectroscopy studies of polymer-silica nanocomposites, /. Phys. Condens. Matter, 19, 205120-1 to 205120-12 (2007b). 

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