What is the science behind polyethylene bonding?

Polyethylene (C20H40) has single bonds from twenty carbon atoms to forty hydrogen atoms. It is a polymer chain of ten linked ethylene (C2H4) monomers, which have two carbon atoms and four hydrogen atoms.
In an ethylene monomer, the two carbons are double bonded to themselves, while the hydrogens are single bonded to the carbons. When the ethylene monomers link to form Polyethylene, however, the bonds turn into all single bonds.