Hydroperoxides

Oxidation Kinetic

Thermomechanical stress during processing cycles accelerates the formation of these reactive sites. Virgin resins contain low levels of these compounds, whereas regrind material often shows higher concentrations due to previous exposure to heat and shear. The increased density of these radical precursors in regrind forces a faster depletion of stabilisers like phosphites and hindered phenols.

Manufacturers track the chemical activity of these intermediates to prevent premature discolouration and loss of impact strength in finished goods.

Polymer Instability

Molecular degradation progresses through a cycle of initiation, propagation, and termination that relies on the cleavage of oxygen-oxygen bonds. When hydroperoxides reach a critical thermal threshold, they break down into alkoxy and hydroxy radicals. These species strip hydrogen atoms from adjacent polymer chains, creating new carbon-centered radicals that continue the cycle of damage.

A moulder managing high-melt-flow polymers must regulate barrel temperatures precisely to slow this rate of chain scission. Control of these radical sources remains the primary method for maintaining the structural integrity of recycled plastic streams.

Processing Impact

Melt stability decreases as the concentration of these internal oxidants rises in the feedstock. Excess levels lead to viscosity fluctuations that manifest as uneven fill patterns and surface defects during high-speed injection cycles. Part specifications require a stable molecular weight distribution that only low levels of these compounds permit.

Residual radical activity after the moulding process often causes long-term brittleness in the field.