Pendant Hydroxy Polyethylene Reactive Additives for Improved Mechanical Properties and Melt Processability of Poly(ethylene terephthalate)/Polyethylene Blends

Reactive compatibilization is an attractive solution to improve the mechanical properties of polymer blends that inherently result from plastic recycling processes. In this study, pendant hydroxy polyethylene reactive additives were synthesized through ring-opening metathesis polymerization (ROMP) and their ability to compatibilize poly(ethylene terephthalate) (PET)/polyethylene blends through reactive compatibilization was evaluated. The ROMP synthesis strategy enabled the deconvolution of the effects of overall number-average molar mass (M_n) and average molar mass between reactive hydroxy groups (M_g) on compatibilization effectiveness. The results of this study suggest a near-optimal M_g ∼ 1 kg/mol where the strain at break (ϵ_b) of the blend with 1 wt % additive is increased significantly (ϵ_b ∼ 280%) over the neat blend without the additive (ϵ_b ∼ 16%), independent of M_n. Near-optimal M_g additives were effective at industrially relevant reaction times of 5-10 min, at loadings as low as 0.5 wt %, and in blends containing one of two different types of PET, suggesting their versatility and commercial applicability. Extensional viscosity was characterized and melt strain hardening (MSH) was observed to be highly dependent on the viscosity ratio between the matrix and dispersed phases, which is a function of temperature. When MSH is present, we show that reactive compatibilizers capable of forming branched reaction products offer an improvement to the MSH, compared to linear analogues. These findings suggest that branched compatibilizers may be advantageous for melt processability of compatibilized recyclates in processes dominated by strong extensional flows, such as film blowing, foaming, and thermoforming.