  Recycling has become a predominant subject in industry and science due to a
rising concern for the environment driven by high production volume of
plastics. Replacement of virgin polymers with their recycled analogs is not
always possible because recycled polymers cannot met the same property profiles
as their virgin counterparts. To avoid deterioration of the mechanical
properties, it is proposed to replace a virgin polymer with a recycled polymer
of another grade whose characteristics (measured in tensile tests) are close to
those of the virgin material. This approach opens a way for the use of recycled
polymers in short-term application, but its suitability for long-term
applications has not yet been assessed. A thorough experimental investigation
is conducted of the mechanical response of virgin high-density polyethylene
(HDPE) used for insulation of pipes and recycled HDPE manufactured from
post-consumer plastic waste (their stiffness, strength and elongation to break
adopt similar values). A model is presented in viscoelastoplasticity of
semicrystalline polymers. Its parameters are determined by matching
experimental data in short-term relaxation and creep tests. The lifetime of
virgin and recycled HDPE under creep conditions is evaluated by means of
numerical simulation. It is shown that the stress-time to failure diagrams for
virgin and recycled HDPE practically coincide.
