Abstract
Awareness of environmental issues has led to increasing interest from composite researchers in using “greener” materials to replace synthetic fiber reinforcements and petrochemical polymer matrices. Natural fiber bio-based thermoplastic composites could be an appropriate choice with advantages including reducing environmental impacts, using renewable resources and being recyclable. The choice of polymer matrix will significantly affect the cost, manufacturing process, mechanical properties and durability of the composite system. The criteria for appropriate monomers are based on the processing temperature and viscosity, polymer mechanical properties, recyclability, etc. This review considers the selection of thermoplastic monomers suitable for in situ polymerization during resin, now monomer, infusion under flexible tooling (RIFT, now MIFT), with a primary focus on marine composite applications. Given the systems currently available, methyl methacrylate (MMA) may be the most suitable monomer, especially for marine composites. MMA has low process temperatures, a long open window for infusion, and low moisture absorption. However, end-of-life recovery may be limited to matrix depolymerization. Bio-based MMA is likely to become commercially available in a few years. Polylactide (PLA) is an alternative infusible monomer, but the relatively high processing temperature may require expensive consumable materials and could compromise natural fiber properties.
Highlights
Fiber-reinforced composite materials have been widely used for marine applications due to their superior resistance to biological and chemical attack in the harsh marine environment [1,2]
This review paper discusses the selection of thermoplastic monomers with the potential for producing natural fiber-reinforced marine composites via in situ polymerization infusion during monomer infusion under flexible tooling (MIFT)
The major mechanical and thermal properties of the candidate thermoplastic polymers are summarized in Table 3 and directly influence the application of thermoplastic composites in the marine environment
Summary
Fiber-reinforced composite materials have been widely used for marine applications (marine renewable energy devices, offshore oil/gas infrastructure, boat hulls, etc.) due to their superior resistance to biological and chemical attack in the harsh marine environment [1,2]. This review paper discusses the selection of thermoplastic monomers with the potential for producing natural fiber-reinforced marine composites via in situ polymerization infusion during MIFT. Key considerations are monomer initial viscosity, process temperature, fiber/matrix interfacial compatibility and bonding, availability of bio-sourced monomer, mechanical and thermal properties of the product, moisture uptake, environmental burdens and recyclability. The mold clamping forces for pressure-driven RTM increase with the area, and RIFT/MIFT soon becomes the only sensible LCM option for the production of large surface area composite structures, for example, boat hulls or wind turbine blades [63,66]. RIFT is used for production with thermosetting resins, and MIFT for the in situ polymerization process to produce thermoplastic matrix composites. The key factors for a successful RIFT/MIFT process are (i) polymer rheology, (ii) reinforcement permeability, which quantifies resistance to resin flow [67], and (iii) processing temperature
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