JEC COMPOSITES MAGAZINE - Issue #48 - May 2009 - 67

Compressive strength was measured according to the ASTM D 3410 standard on the same composite in the longitudinal fibre direction (along the fibre axis). The results show a 15% improvement. even more pronounced (9% higher flexural strength), especially for fracture toughness, which is as high as 26%. Reinforcement mechanism With EpoCyl™ products, the supposed improvement mechanism is related to the crack deflection and crack pinning induced by the presence of carbon nanotubes in the matrix. Due to their high surface area, the energy absorbed by the void formation around CNT is higher than with a conventional toughening agent. This significantly increases the G1C properties of the final composite material. The level of improvement depends on the capacities of the host matrix itself (as is the case with any other toughening agent). Thermo-mechanical performance The coefficient of thermal expansion (CTE) was measured in the transverse fibre direction for configurations without nanotubes and EpoCyl™-based configurations. The results indicated a significant reduction in CTE (about 17%), which is key to the dimensional stability of any composite structure. - Inducing an antistatic behaviour All the EpoCyl™-based products were characterized to investigate the additional benefits of CNT reinforcement in a composite structure. It was observed that the surfaces and the whole structure (volumetrically) of the products become antistatic. This is a key advantage in applications like antistatic coating or E-painting (to prevent paint losses), while also improving surface finish. This is also a solution to improve conductivity in composite materials. - Inducing a fire retardant behaviour CNT reinforcement of composites also improves their fire retardant properties without any additional additives. Preliminary tests showed a significantly improved fire resistance behaviour. The final resin material does not burn or drip. These observations are still under evaluation. Fig. 5: Schematic representation of various mechanism increasing fracture toughness. Results for Sizicyl™ products The sizing’s properties were investigated on glass fibre to demonstrate its reinforcing effect on the final composite. The composites were produced using neat resins or EpoCyl™ formulations (Table 1). Table 1: Final composite material properties. Type of composite Virgin glass Fibre/Epoxy resin Sized glass fibre with CNT/Epoxy resin Virgin glass Fibre/Epoxy resin filled with CNT Sized glass fibre with CNT/Epoxy resin filled with CNT Flexural strength (MPa) 1225.957 G1C (J/m2) 374.6141 In the case of SizyCyl products, the presence of CNTs at the fibre surface (which in the end is at the fibre/matrix interface) increases the interfacial surface due to the high aspect ratio of CNTs. The greater interfacial adhesion surface increases energy absorption during debonding or crack propagation, thereby significantly increasing the interfacial shear strength of the laminates in a composite structure. This fibre sizing mechanism also increases fibre stiffness without chemically damaging treatment at higher temperatures. Such nanoscale reinforcement has an impact on properties like flexural strength (+10%) and fracture toughness (+25%), as summarized in Table 1. 1325.092 414.1454 Opportunities and potential markets As explained before, Nanocyl products and CNT reinforcement can provide high mechanical properties and improved overall performance in composites. Therefore, they are excellent candidates for applications in high-end composite materials. Besides the applications based on the dispersion quality, low viscosity and mode applications, there could be some instant high-end applications. For instance, the Sizicyl™ technology can be applied to carbon fibres to produce higher modulus composite materials without any negative impact on damage tolerance. On the other hand, EpoCyl™ products can be used to 1286.459 467.2778 1350.56 474.375 A significant improvement in flexural strength (8%) and fracture toughness (G1c) (11%) can be seen when combining the sized fibres with a neat resin. With EpoCylTM products, this effect is No48 May 2009 / jec composites magazine 67

JEC COMPOSITES MAGAZINE - Issue #48 - May 2009

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #48 - May 2009