Novel polymeric alloy
Novel polymeric alloy is a polymeric alloy composed of polyolefin and thermoplastic engineering polymer with enhanced engineering properties. NPA was developed for use in geosynthetics. One of the first commercial NPA applications was in the manufacturer of polymeric strips used to form Neoloy® cellular confinement systems (geocells).
Novel polymeric alloy was developed as an alternative to high-density polyethylene (HDPE) in geosynthetics. Although HDPE is widely used due to its low cost, ease of manufacturing and flexibility, its relatively high creep, low tensile strength and sensitivity to elevated temperatures limit its use, for example, in long-term, critical geocell applications.
Used in the manufacture of geosynthetics, such as cellular confinement system, novel polymeric alloy provides higher tensile strength and stiffness, and is more durable over dynamic loading and under elevated temperatures than those made from HDPE. The lifespan of NPA based geosynthetics, such as geocells, makes them suitable for long-term design in infrastructure, such as highways, railways, container yards and high retaining walls.
Production
Novel polymeric alloy is compounded for geosynthetic applications, such as high-modulus geocells or geogrids. In geocell applications strips are co-extruded in multi-layer strips. Outer layers are a blend of polyolefins while the core layer is formed from a high performance polymer. The blend is generally immiscible, where the high performance polymer is dispersed in a matrix formed by the polyolefins. Since polymer blends are basically unstable, they undergo stabilization during melt processing, at a nano-level combined with compatibilized material.The novel polymeric alloy core layer/s is made of a high performance polymer compound with a storage modulus of ≥1400 MPa at 23 °C, measured by Dynamic Mechanical Analysis at a frequency of 1 Hz according to ASTM D4065; or an ultimate tensile strength of at least 30 MPa. The outer layers are usually made of a polyethylene or polypropylene polymer, with a blend or alloy with other polymers, fillers, additives, fibers and elastomers. The high performance alloys of polyamides, polyesters, and polyurethanes are combined with polypropylene, copolymers, block copolymers, blends and/or other combinations.
Manufacture
While most polypropylene homopolymers are too brittle and most polypropylene copolymers are too soft, certain grades of polypropylene polymers are stiff enough for engineering purposes, yet soft enough so that a geosynthetic can be handled for installation. These polymers are modified, via proprietary treatment processes and the addition of additives such as nanoparticles to attain the required physical properties.Unlike low crystalline polymers such as polypropylene, which require a post-extrusion processing such as orientation, cross-linking, and/or thermal annealing, higher crystalline polymers such as novel polymeric Alloy can be extruded as strips and welded in section without post-extrusion treatment. The sheet can be extruded into strips and welded, sown, or bonded together to form geosynthetic products. Such additives (stabilizers for polymers) may be selected from, among others, nucleating agents, fillers, fibers, hindered amine light stabilizers, antioxidants, UV light absorbers, and carbon black in the form of powders, fibers, or whiskers.