Novel polymeric alloy
| NEOLOY | |
|---|---|
| Type | Nano-composite polymeric alloy |
| Main ingredient | Polyolefin |
| Additional ingredients | Polyamides, compatibilizers, anti-toxidants, colorants |
| Density p | 0.96 g/cm3 |
| Tensile strength(σt) | 19-32 MPa |
| Elastic limit/Yield | 12% |
| Glass temperature | 70°C |
| Melting point | >200°C |
| Linear expansion coefficient (α) | 80 ppm°C |
| Source[1] | |
Neoloy is the registered trademark for a novel polymeric alloy (NPA) composed of polyolefin and thermoplastic engineering polymer. It was developed specifically for use in high-strength geosynthetics. The first commercial application was in the manufacturer of polymeric strips used to form cellular confinement systems (geocells).
Neoloy (referred to in published research as Novel Polymeric Alloy – NPA) was developed to replace 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 (Leshchinsky, 2009).[2].
Used in the manufacture of geosynthetics, such as the PRS-Neoweb cellular confinement system, Neoloy provides geocells with a higher Tensile strength and stiffness, and are more durable over dynamic loading and under elevated temperatures than those made from HDPE (Han, 2011).[3] The lifespan of Neoloy-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
Neoloy 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 (an alloy), 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.[4]
The Neoloy 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 (DMA) 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.[5]
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 Neoloy 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 (HALS), antioxidants, UV light absorbers, and carbon black in the form of powders, fibers, or whiskers.
Properties
The polyolefin in the Neoloy polymer blend provides stress cracking resistance, hydrolytic resistance, very low temperature functionality and tear resistance, while the polyamide engineering polymer provides strength, stiffness, retention of mechanical strength at elevated temperatures, creep resistance and long-term dimensional stability. Neoloy has a coefficient of thermal expansion CTE less than about 80 ppm/°C; resistance to acidic media greater than polyamide 6 resin and/or resistance to basic media greater than PET resin; resistance to hydrocarbons greater than that of HDPE; creep modulus of > 400 MPa at 25°C at 20% of yield stress load for 60 minutes (ISO 899-1); and 1 percent secant flexural modulus > 700 MPa at 25°C (ASTM D790). Neoloy has a tensile strength in the range of 19.1 to 32 MPa with an elastic modulus of 440 to 820 MPa (at 2% strain).[1]
Applications
Neoloy was developed for a high-modulus geosynthetics, including geocells, geogrids and geomembranes, which require higher strength, stiffness and durability. In a geocell application, the high modulus of Neoloy means stiff and strong cell walls, which provide a very high elastic response to dynamic loading even after millions of cycles without permanent plastic deformation.[6] The strength and stiffness of Neoloy, as measured by tensile strength, long-term resistance to deformation, coefficient of thermal expansion (CTE) and performance at elevated temperatures (storage modulus), provides a performance lifespan previously available in geocell applications. This is a notable development in the geosynthetic / geocell industry, allowing the use of geocells for example, in structural reinforcement for flexible pavements, earth retention walls, and other heavy-duty geosynthetic applications, where long-term durability under heavy loading is critical (Leshchinsky, et al, 2009). At the same time, Neoloy properties enable the manufacture of lighter geocells which retain suitable engineering strength for moderate loading as typically found in slopes, channels and retaining wall applications.
See also
References
- ^ a b Halahmi, I., Erez, O., Erez, A., (2009, 2010), High Performance Geosynthetic Article , US Patents 7,674,516 B2, 7,541,084 B2
- ^ Leshchinsky, D. (2009) “Research and Innovation: Seismic Performance of Various Geocell Earth-retention Systems,” Geosysnthetics, No. 27, No. 4, 46-52
- ^ Han, J., Pokharel, S.K., Yang, X. and Thakur, J. (2011). “Unpaved Roads: Tough Cell – Geosynthetic Reinforcement Shows Strong Promise.” Roads and Bridges. July, 49 (7), 40-43
- ^ Halahmi, I., Erez, O., Erez, A., (2011), Process for Producing Compatibilized Polymer Blends, US Patent 8,026,309 B2
- ^ Halahmi, I., Erez, O., Erez, A., (2012), Multi-layer Sandwhich System for Geocells, US Patent 8,173,241 B2
- ^ Pokharel, S.K., Han, J., Manandhar, C., Yang, X.M., Leshchinsky, D., Halahmi, I., and Parsons, R.L. (2011). “Accelerated Pavement Testing of Geocell-Reinforced Unpaved Roads over Weak Subgrade.” Journal of Transportation Research Board, the 10th International Conference on Low-Volume Roads, July 24-27, Lake Buena Vista, Florida, USA