The absorption of humidity together with the presence of oxygen and moisture can produce molecular reorganization, from the breakdown of a molecular chain to its oxidation [ 9 9 Canevarolo, S. Fundamentals of degradation and stabilizations of polymers. La Mantia Ed. Shrewsbury: Rapra Technology. Another factor that may influence the polymer life cycle is related to the effect of stress cracking, which may influence the macroscopic properties of the tissues, such as the weave and warp of the fabric [ 35 35 Zhang, H.
Comparison and analysis of thermal degradation process of aramid fibers. Journal of Fiber Bioengineering and Informatics, 3 3 , Thermal degradation process os polysulphone aramid fiber. Thermal Science, 18 5 , The degradation process may also cause changes in the properties of the polyaramide, such as loss of brightness, changes in color, cracking and the decrease of mechanical properties [ 26 26 Wang, H. The blades of armor are not exposed directly to solar radiation, nor direct exposure to weathering, since the blades are arranged in layers, coated by at least two additional layers of different impermeable fabrics [ 1 1 Companhia Brasileira de Cartuchos — CBC.
Part A, Applied Science and Manufacturing, 37 9 , In this sense, the objective of this study is to evaluate the loss of the mechanical properties of polyaramide fibers used as raw material for the manufacture of ballistic armor with different dates of manufacture and use after exposure to natural weathering. The polyaramide fibers came from tissues samples of ballistic armor that was more than 5 years old, that had been disposed of by the logistic center of the Brigada Militar of the State of Rio Grande do Sul.
The fiber samples had a dtex of - unused vest and , for a vest that was normally used for five years , referred to as K10 and K05 respectively. Teijin aramid ballistics material handbook. ASTM D standard pratice for outdor weathering of plastics. The main characteristics of the fibers used for the tensile test are summarized in Table 1 and Figure 1 showing the difference of the weave of the polyaramide fabric samples from left and right fabrics.
This allowed for a normal incidence of solar radiation over the entire surface of the samples. Figure 2 shows the climatic conditions maximum Precipitation and maximum UV index UVI , moisture and average total monthly rainfall during the total period studied.
It was observed that the highest temperatures occurred during the months of November to March , but the maximum temperature in January , which reached over to January , and between September to January the frequency of rainfall was higher, reaching mm values. Regarding the UVI, the values were high during the spring and summer, reaching values over 12, which is classified as extreme. In addition, the gloss G of the samples was measured.
As can be observed in Figure 3 , the fibers were glued on to a cardboard base, with a grammage of g. Tensile tests of polyaramide fibers were carried out according to ASTM DM in a universal test machine using specimens tested with a length of mm and a load cell of N, an extension speed of 5 mm min -1 , and a gauge length of 25 mm. Each tensile value reported is the average of a 10 specimen test.
For the scanning electron microscopy SEM analysis, the samples were deposited in a carbon type stuck to stub, metalized with gold. Porto Alegre: Bookman. For the calculation of the polyaramide fiber diameters a 50 micron scale was used and based on the image it was divided into an area of nine equal divisions containing a significant amount of fibers for analysis, the average was obtained.
The procedure was repeated in the delimited areas, and the mean diameter was calculated. The advantage of this method was the correct division of the zones with a low error in the diameter estimation, with two weights, considerably reducing the error.
Figure 4 shows the results of the colorimetric parameters of the polyaramide K05 and K10 samples before and after exposure to natural weathering. These color changes indicate chain cleavage due to the hydrolytic degradation of the polyamides. Such photo degradation features are reported by Bittencourt [ 12 12 Bittencourt, G. The change of coloration, as well as the loss of brightness, represented by the decrease of Luminosity c the fiber became more opaque and increase of fiber roughness.
The decrease of the Gloss d , can be attributed to hydrolysis too, in addition to this, there was environmental stress cracking too, due to the climatic conditions to which they were exposed, greater periods of precipitation and temperature variations, which depleted the fibers, being faster in samples k The signs of degradation reached the superficial layers of the tissues, causing an initial discoloration, facts reported by Wang et al.
The initial colorimetric results of the degradation of the samples were very similar for the K05 and K10 samples. However, due to the difference in the fabric weaving and the yarn, after two months of continuous exposure to the weather, it was observed that the brightness indicators related to the roughness were not uniform. Surface nanostructuring of kevlar fibers by atmospheric pressure plasma-induced graft polymerization for multifunctional protective clothing.
Maguire-Boyle , Michael V. Liga , Qilin Li , Andrew R. Nanoscale , 4 18 , Preparation of magnetically separable N-halamine nanocomposites for the improved antibacterial application. Journal of Colloid and Interface Science , 2 , Synthesis of N -halamine-functionalized silica—polymer core—shell nanoparticles and their enhanced antibacterial activity. Nanotechnology , 22 29 , Permeability and chemical analysis of aromatic polyamide based membranes exposed to sodium hypochlorite.
Antimicrobial polyethylene terephthalate PET treated with an aromatic N -halamine precursor, m -aramid. Journal of Applied Polymer Science , 6 , Improved Antimicrobial Efficacy of m-Aramid. Textile Coloration and Finishing , 21 5 , Broughton , S. Worley , T. Journal of Engineered Fibers and Fabrics , 2 4 , Pair your accounts. Your Mendeley pairing has expired. Please reconnect. This website uses cookies to improve your user experience.
By continuing to use the site, you are accepting our use of cookies. The fibres can be spun or woven into mats or fabrics to exploit these exceptional properties. Kevlar is made by a condensation reaction of an amine 1,4-phenylene-diamine and and acid chloride terephthaloyl chloride.
The kevlar chains are relatively rigid and tend to form mostly planar sheets, similar to those of silk. This is due to the para -orientation of the benzene rings. When kevlar is spun the chains lock together via H-bonds to form a sheet that has a very high tensile strength. The sheets also stack radially, like the spokes on a wheel, allowing additional interactions between the face-to-face aromatic groups on neighbouring sheets to help to increase the strength of the overall fibre. As mentioned above, the most well-known application for kevlar is in personal armour, such as bulletproof vests, combat helmets, face-masks, etc.
But Kevlar can also be used in sports equipment, such as inner linings for bicycle tyres, tabletennis bats, bow strings for archery, paraglider suspension lines, and motorcycle safety clothing. Believe it or not, body armor is manufactured with an expiration date, which is usually around 5 years after a vest is produced. You might have thought that expiration dates are limited to items like food and medicine, but body armor and other similar safety products also have a shelf life.
This is because the chemical compounds that make up a vest, such as industrial fiber or Kevlar, degrade over time. A number of other factors can speed up the degradation process, too. This also means that storing your vest in a humid location can quicken the degradation process.
Using your vest in environments with high exposure to ultraviolet radiation can also shorten shelf life. Commonly, body armor vests are exposed to UV rays when worn out in the sunlight for extended periods.
Even something as simple as a change in your weight can diminish the protective quality of your gear. If a vest presses too snuggly or not snuggly enough against your body, stress may be put on the ballistic panels as they move around inside the carrier.
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