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Henkel has developed the Loctite Benzoxazine (BZ) composites family which includes prepregs, infusion resins, film adhesives and tooling materials.
According to Henkel, Loctite BZ is developed specifically for the aerospace industry and offers a solution over commonly used epoxies, phenolics and BMIs, in areas including product performance, storage, processing and health and safety. It says qualifications for benzoxazines prepregs are currently in progress for both the Airbus A380 and Comac C919, with the material fully tested according to major OEM programs and material systems baselines.
Henkel explains benzoxazines can compete in all ranges of service temperatures and toughness for both primary and secondary structure applications. Formulated and supplied in prepreg format, all BZ prepreg systems are produced using hotmelt, meaning no solvent is needed.
Furthermore, Henkel claims it has excellent storage life stability. When subject to thermal analysis over one year, BZ prepreg formulas demonstrate minimal change in differential scanning calorimetry (DSC) characteristics at room temperature. They also maintain their interlaminate shear strength (ILSS) after 12 months with just a slight drop in the flow characteristics of the resin.
The company states BZ provides superior stiffness and strength to weight ratios compared to metals, enabling for flexible design and delivering weight savings of up to 30%. When compared to epoxies, BZ shows outstanding fire and smoke performance and excels still further with regards to non-flaming and flaming toxicity, typically emitting 2% or less of the parts per million limit for each toxin.
Another advantage, Henkel states, is the low cure shrinkage. After measuring density before and after cure, BZ demonstrates shrinkage of only 1.06%, compared to equivalent epoxy shrinkage of between 4-5%.
Henkel explains that in addition, the lower heat of cure of the BZ system offers a lower exotherm potential. The material can demonstrate a heat of cure of only 106 Jules/Gram, compared to 210 joules/gram in a typical epoxy prepreg system. BZ systems also have a moisture pick-up rate of only 0.7-0.9%, compared to a typical toughened epoxy system’s rate of up to 3%. This means the material will pick up less weight over time, and demonstrate an improved hot/wet performance.
Henkel states Loctite BZ prepregs are optimised for automated processing, with its high service temperature iteration performing very well with both automated fibre placement (AFP) and automated tape-laying (ATL) even on the first round, and demonstrating good tack and drape. Machines used to prove AFP capability include trials at MTorres, Ingersoll and Electro-Impact, with no change in processing necessary compared to standard prepreg, apart from an adjustment to the correct size.
Loctite BZ prepreg resins eliminate the need for refrigerated shipping and storage, enable increased service temperatures, lead to improved safety and lower residual stress, contribute to better thermal stability and save at least 30% of weight compared to conventional metal structures.
To conclude, Henkel claims BZ demonstrate high hot/wet mechanical properties, ambient stability, excellent FST performance and low cure exotherm and shrinkage. In addition, the resins have proven highly successful in both automated processing and OOA, allowing for multiple systems capable of providing a balance of service temperature, toughness and processing.
Photo provided by Henkel
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