The response of aerospace composites to temperature and humidity
12.10 Nonaqueous environments
Organic solvents are used in paints, in paint strippers and as degreasing agents, so the resistance of organic polymer-based composites to these materials should be discussed. Cross-linked thermoset resins or crystalline thermoplastics do not dissolve in common organic solvents. However, the amorphous regions of the thermoplastics and the cured thermosets used as composite matrices will swell after contact. The solvent will tend to dissolve (i.e. diffuse) into the polymer in an analogous mechanism to moisture diffusion but at a higher rate. The degree of swelling will be maximised in contact fluids with a similar solubility parameter as the polymer matrix. The solubility parameters of the matrix and the solvent can be estimated using simple additive principles [45]. The concept of solubility parameters is simply described by Eqn (12.16):
where δsolvent and δpolymer are the solubility parameters.
The maximum plasticisation of the matrix will occur under these conditions which will lead to a high potential to creep under off-axis loads. The residual stress state will also be significantly modified, as discussed in this chapter.
Schulte [46,47] has demonstrated how different organic solvents, such as hydraulic fluid encountered in the aerospace structures, lead to a reduction in the secant modulus of ±45° glass fibre laminate under flexural fatigue and the number of cycles to failure. The matrix in this case was a polyether imide (PEI) which is plasticised by ingress of the fluid. A reduction in the matrix modulus means that the shear strength of the matrix will also be reduced with the consequence that the failure mechanism in flexure will change from matrix-fracture to delamination.
Matrix swelling also contributes to the loss of durability in the 0° composite where plasticisation causes buckling in the compressive face of the coupon [46,47]. This occurs because in compression, the plasticised matrix is unable to support the reinforcement.
The reader should be reminded that PEI is an amorphous polymer and is much more susceptible to solvents than partially crystalline polymers such as PEEK, which are used for structural composites.
Weatherhead [48] and Jones [7] provide a survey of the durability of resins to a range of environments.
Hepatic Toxicology
J.R. Roede, … D.R. Petersen, in Comprehensive Toxicology, 2010
9.26.5.2 Trichloroethylene
Trichloroethylene (TCE) is a widely used solvent since the early 1900s and is a highly effective degreasing agent in a variety of industrial settings. TCE has also been used as a dry cleaning solvent, an ingredient in printing inks and paints as well as a general anesthetic or analgesic. TCE is not believed to occur in nature; however, it has been found in both ground and surface waters as disposal waste from manufacturing establishments. Whereas the use of TCE in the United States has declined since the 1970s, human exposure remains a concern (Bakke et al. 2007).
Routes of exposure to TCE include common occupational exposures, such as inhalation and dermal absorption, and ingestion due to contaminated ground water (Bakke et al. 2007). TCE is primarily metabolized by CYP450 enzymes with CYP2E1 being the primary isoform responsible for biotransformation of TCE. CYP2E1 metabolizes TCE into trichloroacetaldehyde (chloral), which is the major reactive metabolite. Chloral is then further metabolized to trichloro- or dichloroacetate (Costa et al. 1980; Elfarra et al. 1998; Lash et al. 2000).
Owing to the fact that the metabolism of TCE yields a reactive metabolite, chloral, binding of this metabolite to cellular macromolecules such as proteins can lead to the alteration of normal cellular function (Halmes et al. 1996). For instance, binding of chloral to lysine residues of proteins could cause an alteration in or inhibition of that protein’s normal function. In this context, TCE-derived metabolites have been implicated in TCE-induced liver cancer in mice (Elfarra et al. 1998). Metabolism of TCE can also lead to oxidative stress and lipid peroxidation resulting in the production of other aldehydes such as malondialdehyde (MDA) and 4-HNE. As outlined above, these newly generated aldehydes can then modify cellular proteins resulting in altered homeostasis and/or the generation of haptens resulting in an immune response (Wang et al. 2006).
Advances in TCE Toxicology
Yan Jiang, … Tao Chen, in Advances in Molecular Toxicology, 2017
1 Introduction
Trichloroethylene (TCE), a volatile organic solvent, is widely used in industry as a metal-degreasing agent and in the production of chlorinated chemical compounds. As a result of the widespread use, TCE is a common contaminant in the atmosphere, ground water, drinking water, and food [1]. Occupational exposure to TCE occurs through inhalation and dermal contact, and the general public may be exposed to TCE through inhalation and ingestion of contaminated water and food. For all the three routes of exposures (ingestion, inhalation, and dermal contact), the metabolic pathways of TCE are similar [2]. TCE has been classified as carcinogenic to humans (Group 1) [3,4]. TCE also poses noncancer risks to the central nervous system, kidney, liver, immune system, reproductive system, and development of the fetus. This review will focus on the carcinogenicity (kidney and liver cancer), the immunotoxicity, and the cardiac developmental toxicity of TCE.
- The response of aerospace composites to temperature and humidity - December 21, 2024
