In situ grafting and compatibilization of polyethylene/EVA blends: a low-cost alternative to Surlyn ionomers in multi-layer impact pipes

Research background and core ideas

According to the research published in Volume 163 of Polymer Testing (author) Ali Khalili Gashtroudkhani、Nidal H.Abu-Hamdeh、Mohammed N.Ajour）， The blend system of polyethylene and EVA (ethylene vinyl acetate copolymer) has potential applications in high-performance pipes such as multi-layer impact pipes, but the insufficient compatibility between the two will limit the interface bonding and final performance. The study proposes the formation of in-situ graft copolymers as a means of reactive compatibilization of PE/EVA blends and positions it as a low-cost alternative to Surlyn ionomer systems.

Formula and processing points

The technical path of this work is not to add pre made compatibilizers, but to promote the in-situ generation of graft copolymers during the blending process, thereby establishing a stronger connection at the interface between PE and EVA phases.

. The value of this approach lies in simplifying the raw material system, reducing reliance on high priced ionomer compatibilizers, while maintaining the interlayer adhesion and mechanical integrity required for multi-layer pipes. For multi-layer molding processes such as extrusion and co extrusion, the reaction window for in-situ capacity expansion is closely related to processing temperature and residence time, and formula design needs to be considered in conjunction with processing conditions.

The significance of polymer aging and stabilization technology

From the perspective of polymer aging and weather stability, the interface state of PE/EVA blends directly affects their long-term performance.

. The weak areas of interface bonding often become channels for stress concentration and medium penetration, which are more prone to chain breakage and cross-linking under hot oxygen and photo oxygen conditions, resulting in decreased mechanical properties, surface pulverization or cracking. Improving interfacial bonding through reactive capacity expansion can help reduce such weak links and provide a more uniform substrate environment for the protective effects of antioxidant and photostable systems. In actual formulations, the vinyl acetate chains of EVA may participate in side reactions such as deacetylation at high processing temperatures, which puts higher demands on processing stability. At this point, the combination of processing stabilizing agents and antioxidant systems needs to balance color and melt flow maintenance during the melting processing stage, as well as thermal oxygen protection during the long-term use of the product. If the multi-layer impact tube is facing outdoor or illuminated environments, the weather resistant and stable design also needs to introduce a composite system of HALS (hindered amine light stabilizer) and UVA (ultraviolet absorber), and consider the distribution behavior of additives in the PE and EVA phases – the interface area expands after capacity expansion, and the distribution and migration path of additives change accordingly, which may affect the light stability efficiency.

Characterization and follow-up focus

This study uses in-situ graft copolymer formation as evidence of compatibilization and belongs to the work of formulation and performance level.

. For stabilization technology, it is worth paying attention to the performance retention of the expanded blend under accelerated aging conditions (thermal oxidation, UV), as well as the enrichment or dissipation of antioxidants and light stabilizers in the interface region. These information need to be confirmed through characterization methods such as infrared spectroscopy, thermal analysis, mechanical property tracking, and surface morphology observation. As far as the current source information is concerned, the study has not provided specific formulas for aging test data or stable systems, and the relevant conclusions should be limited to the aspects of capacity expansion and cost substitution.

Industry Insights

This work suggests that in the field of polyolefin blending modification and multi-layer pipe materials, reactive compatibilization can improve compatibility without relying on ionomer compatibilizers, thereby reducing raw material costs.

. For the polymer additive industry, this means that changes in formulation systems will shift the focus of stabilization requirements: interface engineering and the design of antioxidant systems, HALS/UVA complex systems need to be considered simultaneously to support the stable performance of products during processing and long-term service.

Information source:Reactive compatibilization of Polyethylene/EVA blends via in-situ graft copolymer formation: A cost-effective alternative to surlyn ionomers for high-performance multilayer shock tubes， Organized by Herun Chemical.