JEC COMPOSITES MAGAZINE - Issue #43 - September 2008 - 58

KNOW-HOW Materials g…/… Development of helicopter blade coatings Fig. 4: Change in tensile strength, hardness, and elongation after water immersion blade led to a significant reduction in manufacturing costs, weight savings, and erosion protection properties verified by substantial testing panels. The programme was then terminated because of changed corporate priorities and the technology was never commercialized. Some properties of the Lonzacure-cured Airthane PET-91A elastomer are given in Table 2a and 2b. Multiple variants of both prepolymer and cure options are commercially available. NAT intends to build on the unrealized potential of this group of elastomers based on the commercially available materials, and to enhance their heat conductivity properties. Tab.2a: Processing conditions Resin name Lonzacure MCDEA level, 95% stoichiometry (%) Airthane temperature (°C) Lonzacure temperature (°C) Process temp. 17.1 80 100 4 130 30 48/130 Adding even moderate amounts of polybutadiene resin to polyester polyol-based polyurethanes markedly improves the hydrolytic stability of the cured polyurethane. Figures 4 show test results from two comparable polyurethane systems containing a 24.4 wt. percent polybutadiene resin/75.6 wt. percent polyester polyol mixture and based only on polyester polyols. High hydrophobicity The core polybutadiene aliphatic chain imparts significant hydrophobic properties to polybutadiene-based urethane as compared to traditional urethanes. Sand bounces off the fractures upon impact, while raindrops change shape and continue to penetrate the substrate. Therefore, improved hydrophobic properties are essential for the protection from rain erosion. Additionally, more hydrophobic materials will be less prone to icing while facilitating the de-icing procedure. Pot life (min.) - 80°C Mould temperature (°C) Demould time (min.) Post-cure (hrs./temp. °C) Tab.2b: Selected elastomer properties Hardness (A/D) Modulus (Pa) 100% elongation (°C) 200% elongation (°C) 300% elongation (°C) Elongation (%) Tear resistance (PLI)(°C) Die C Split/trouser Airthane temperature (°C) 582 57/86 92/42(°C) .875*104 1,485 1,870 3.58*104 479 Compressive stress (Pa) 5% deflection(°C) 10% deflection(°C) 15% deflection(°C) 20% deflection(°C) 25% deflection Compression set (%) Rebound (%) NBS abrasion index 254.5*104 419.3*104 578*104 .76*104 1*104 13.8*104 39.3*104 172.4*104 Low-temperature flexibility Another attribute of polybutadiene-resin-based polyurethane systems is their outstanding properties at low temperature. This characteristic is attributable to the rubbery polybutadiene backbone. Many polyurethane elastomers derived from polybutadiene resins have brittle points as low as -70°C. This characteristic also contributes to excellent thermal cycling properties. Adhesion properties Adhesion strength to both galvanized steel and aluminium is high, characterized by a lap shear within (758-1172)*104 Pa (ASTM D102). It changes little with ageing, water immersion at room temperature and boiling point, and salt water immersion. Thermally-conductive materials Conductive polymer composites are typically formed by adding thermally-conductive fillers to a polymer matrix. For instance, various carbon fillers are frequently used to increase a composite’s thermal and electrical conductivity. Table 3 lists the thermal conductivity of some common materials relevant to the context of this project [8]. The three fillers selected for this project are pitchbased carbon fibres, carbon black, and synthetic graphite. Pitchbased carbon fibres have a unique set of properties that are not easily attainable by polyacrylonitrile(PAN)-based carbon fibres. For example, PAN-based fibres have a maximum modulus of about 650 GPa, whereas pitch-based fibres can reach 1000 GPa. Pitch-based fibres are also significantly more thermally and electrically Airthane PET-91A-based elastomers This approach was thoroughly validated by the General Electric Company in the late 1990s as part of a programme for the construction of lightweight aircraft engine blades [7]. Through rigorous trials, a material with superior erosion characteristics was obtained from TDI and TMEG pre-polymers, a component marketed by Air Products and Chemicals under the name Airthane PET-91A. After cure by Lonza’s Lonzacure bis-dianiline diamine curative, the resulting elastomer, combined with N-phenylbenzamine (antioxidant) and Tinuvin 765 (hindered amine light stabilizer), was moulded into the blade metal core scaffold. The new composite JEC Composites Magazine / No43 September 2008

JEC COMPOSITES MAGAZINE - Issue #43 - September 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #43 - September 2008