Aramids water absorption

The tensile strength of aramids are comparable to cast metals. In additions, they exhibit low creep and low water absorption. Therefore, these materials... 

Katayama J, Ohki Y. Comparisons of partial discharge resistance and dielectric properties after water absorption between polyetherimide and aramid insulating papers. lEEJ Trans Fundam Mater 2013 133(2) 51-6. 

Drilling and machining can damage composites. Several techniques exist for producing quality holes in composites. Carbon, aramid, and boron fiber reinforced materials each require different drilling methods and tools. When composites are cut, fibers are exposed. These fibers can absorb water, which weakens the material. Sealants can be used to prevent moisture absorption in the clearance hole. Sleeved fasteners can also provide fits that reduce water absorption as well as provide tightness. 

Tanaka K, Minoshima, KM, Grela V et al (2002) Characterizati(Hi of the aramid/epoxy interfaciai properties by means of pull-out test and the influence of water absorption. Comp Sci Technol 62 2169-2177... 

Kawagoe M, Hashimoto S, Nomiya M, Morita M, Qiu J, Mizuno W, Kitano H (1999) Effect of water absorption and desorption on the interfacial degradation in a model composite of an aramid fibre and unsaturated polyester evaluated by Raman and FT infra-red microspectroscopy. J Raman Spectrosc 30(10) 913-918... 

An aramid elastomer sample immersed in water at 23 C showed a weight gain of 1.19% for 25 h, and of 1.40% for 200 h. No weight gain after the 200 h immersion has been observed, indicating that 1.40% is the maximum value of water absorption [44]. 

Chemical properties of type II aramid elastomers have been reported in [43]. Water absorption tests were conducted at RT and at 100% relative humidity. The water absorption of a PTMO-containing aramid elastomer was only 1.0 wt%, while that of a poly(ethyleneoxide) (PEO)-containing elastomer was 80.5 wt% [43]. 

The hydrophilieity of the amide group leads to a significant absorption of water by all aramids. While the ehemistry is the driving factor, fiber structure also plays a very important role for example, Kevlar 29 absorbs 7% water, Kevlar 49 4%, and Kevlar 149 only 1%. Fukuda explored the relationship between fiber crystallinity and equilibrium moisture in great detail [23]. 

Aramid fibres absorb about 5% water, which can sometimes affect then-performance in aqueous liquids [24]. Some reinforced plastics applications involve repeated soak-dry cycles and it can be the drying stage, rather than absorption that causes damage. If the second absorption cycle produces more absorption in a given time than the first cycle did, it usually indicates permanent damage. 

Hydrophylicity of amide linkage leads to moisture absorption by all aramids. The skin-core structure of the p-aramid fibers plays an important role in the moisture absorption, which is critical for many structural applications of the FRP on their basis. Thus, Fhkuda and Kawai found that the ultrahigh modulus Kevlar 149 has a moisture uptake of 1% (20°C, 55% relative humidity), while in the regular brand Kevlar 29 it is -7% under the same conditions [34], Apparently, above a certain concentration, the water molecules could upset the intermolecular hydrogen bond formation (Figure 8.2) and affect the mechanical properties, as seen by the comparison of the mechanical properties of Kevlar 29 and Kevlar 149. The same authors found that the diffusion coefficient through the skincore structure of the Kevlar fiber is also of importance in the skin the trend is Kevlar 149 > Kevlar 29 > Kevlar 49 and in the core it is reversed Kevlar 29 > Kevlar 49 > Kevlar 149. 

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