Editing Kevlar (section)

==Structure and properties==
[[Image:Kevlar chemical structure H-bonds.svg|thumb|upright=1.8|Molecular structure of Kevlar: '''bold''' represents a [[monomer]] unit, '''dashed''' lines indicate hydrogen bonds.]]
When Kevlar is [[spinneret (polymers)|spun]], the resulting fiber has a [[tensile strength]] of about [[Pressure|{{cvt|3620|MPa|psi}}]],<ref>{{cite journal | last1 = Quintanilla | first1 = J. | year = 1990 | title = Microstructure and properties of random heterogeneous materials : a review of theoretical results | journal = Polymer Engineering and Science | volume = 39 | issue = 3| pages = 559–585 | doi = 10.1002/pen.11446 }}</ref> and a [[relative density]] of 1.44 (0.052&nbsp;lb/in<sup>3</sup>).  The polymer owes its high strength to the many inter-chain bonds. These inter-molecular [[hydrogen bonds]] form between the carbonyl groups and N''H'' centers.  Additional strength is derived from [[aromatic stacking interaction]]s between adjacent strands. These interactions have a greater influence on Kevlar than the [[Van der Waals bonding|van der Waals]] interactions and chain length that typically influence the properties of other synthetic polymers and fibers such as [[ultra-high-molecular-weight polyethylene]]. The presence of [[Salt (chemistry)|salt]]s and certain other impurities, especially [[calcium]], could interfere with the strand interactions and care is taken to avoid inclusion in its production. Kevlar's structure consists of relatively rigid molecules which tend to form mostly planar sheet-like structures rather like [[silk]] protein.<ref>Michael C. Petty, ''Molecular electronics: from principles to practice'', John Wiley & Sons, 2007, p. 310</ref>