Atmospheric Plasma Treatment of Composites or Composite Materials is a broad field ranging from carbon and glass fiber based materials, metal and ceramic composites, composite building materials such as cements and concrete, reinforced plastics to organic (carbon-based) nanomaterials such and carbon nanotubes (CNT) and graphene. Atmospheric plasma can be utilized to clean, activate and modify surfaces to maximized composite bond performance in applications such as aircraft and space structures as well as UAVs, drones, automotive, racing and high performance sporting goods equipment.
The main benefit of atmospheric plasma composite materials processing is the ability to transition to out-of-autoclave (OOA) manufacturing processes for composites creating new market opportunities by offering cheaper processes with unlimited size options. Atmospheric plasma treatment of composites offers increased reliability and bond performance over traditional composite bonding processes such as sanding, grit blasting and toxic wet chemistry surface preparation methods. Automated non-contact surface preparation of composites with atmospheric plasma allows for lower equipments costs, minimal consumables and unlimited three dimensional (3D) surface profile processing.
Intrface Technologies has developed a proprietary atmospheric plasma process for the treatment hybrid thermoplastic polypropylene composites. Polypropylene based composites can offer cost advantages over traditional carbon and glass fiber composites but are difficult to bond. As with other low surface energy (LSE) plastics such as thermoplastic polyolefin (TPO) and polyethylenes (HDPE), polypropylene traditionally had to be mechanically attached or welded since true adhesive bonding did not work well with these materials. Bolts, clips and screws can be used with virtually any surface but they require additional steps to mold or create features for the attachment. Mechanical attachments can lead to stress concentrations which may result in plastic cracking and premature failures, and often result in unsightly and unnecessarily heavy surfaces.
High performance thermoplastics such as PEEK (Polyether ether ketone) and other aromatic polyethers are also difficult to to bond due to their low surface energy. PEEK and is used to fabricate items used in demanding applications, including bearings, piston parts, pumps, HPLC columns, compressor plate valves, and cable insulation and is considered an advanced biomaterial used in medical implants. Atmospheric plasma treatment of PEEK greatly increases surface energy and results in greatly improved bond as well and painting, coating, marking and printing performance.
Atmospheric plasma treatment of composites offers a clean, safe and non-contact surface preparation method the maximize reliability and bond performance of most composite materials. Contact us to discuss your composite bonding application needs.
Related articles:
- H.M. Saleem Ibal, S. Bhowmik, R. Benedictus., “Surface modification of high performance polymers by atmospheric pressure plasma and failure mechanism of adhesive bonded joints,” International Journal of Adhesion and Adhesives (Impact Factor: 2.22). 09/2010; 30(6):418-424. DOI: 10.1016. Abstract: In this investigation, the effects of atmospheric pressure plasma treatment on the surface energy of polyetheretherketone (PEEK), carbon fibers (CF) and glass fiber (GF) reinforced polyphenylene sulfide (PPS) are studied. A substantial improvement in the surface energy of these materials is observed after the atmospheric plasma treatment. It is observed that the polar component of surface energy is responsible for the increase in total surface energy of these materials. To make a comparison of atmospheric plasma treatment and low pressure plasma treatment on the surface energy, PEEK surface is also modified by low pressure plasma. It is observed that the surface modification of polymer by atmospheric pressure plasma is more effective in comparison to low pressure plasma both in terms of improvement of surface energy and bonded joint strength. Scanning electron microscopy of untreated and atmospheric plasma treated specimens is carried out to examine the surface morphology. After atmospheric plasma treatment, increased surface roughness is observed which helps in improving the adhesion properties. The improvement in adhesion properties of these materials is correlated with lap shear strength of adhesive bonded joints. Bonded joints are fabricated by employing recently developed ultrahigh temperature resistant epoxy adhesive. Tensile lap shear testing is also carried out using PPS-CF and PPS-GF as substrate materials. Lap shear tests results for these materials show three to four times improvement in joint strength after atmospheric plasma treatment. Finally, the fractured surfaces of the joints were examined by scanning electron microscope to understand the failure mechanism.Surface modification of high performance polymers by atmospheric pressure plasma and failure mechanism of adhesive bonded joints.
- Chandrashekar, A., Ramachandran, S., Pollack, G., Lee, J. S., Lee, G. S., and Overzet, L J., “Forming carbon nanotube composites by directly coating forests with inorganic materials using low pressure chemical vapor deposition,” Thin Solid Films 517, 525 (2008). Abstract: Low pressure chemical vapor deposition has been used to fill carbon nanotube (CNT) forests with inorganic materials (polysilicon and silicon nitride). Forest filling proceeds by deposition around individual CNTs. As the coating thickness around each CNT increases, the free volume between adjacent nanotubes is filled and finally results in a contiguous composite film. The process maintains the forest height and alignment; however, the coating thickness around the CNTs is in general smaller at the base of the forest than it is at the top. This can cause a contiguous solid film to form at the top of the forest while the forest is only partially filled at the base. Once the top of the forest becomes filled, it prevents growth from occurring at the base. Consequently, the growth process can cap the top of the forest and leave voids between thinly coated CNTs at the base. Such composites have reduced hardness (4 GPa or less). Depositing at reduced temperatures and/or decreased precursor gas flow rates reduces the void fraction through improving the step coverage modulus. This allows one to produce thick (> 50 μm) polysilicon-CNT composite films having hardness approximately equal to that of polysilicon thin films (12.4 GPa).
- Hicks, R. F., Babayan, S. E., Penelon, J., Truong, Q., Cheng, S. F., Le, V. V., Ghilarducci, J., Hsieh, A. G., Deitzel, J. M., and Gillespie, J. W., “Atmospheric plasma treatment of polyetheretherketone composites for improved adhesion,” SAMPE Fall Technical Conference Proceedings: Global Advances in Materials and Process Engineering, Dallas, TX, CD-ROM pp. 9 (2006). Abstract: A handheld atmospheric plasma has been developed to treat polyetheretherketone (PEEK) composites. The instrument produces a plasma beam that covers a circular area 2.5 cm in diameter. The plasma is fed with 30 L/min of helium and 0.45 L/min of oxygen, and is supplied with 80 W of radio frequency power (13.56 MHz). The plasma beam was swept over the composite surface to activate it for bonding. Following treatment, 3M AF-563 adhesive film was applied to 2.5 × 17.8 cm 2 strips of PEEK. The strips were joined together and cured, and a series of lap shear tests (ASTM D-3165) were performed. Plasma treated samples failed cohesively and showed average lap shear strengths of 43.2±0.6 MPa, whereas the untreated samples failed adhesively at much lower shear strengths. Environmental testing revealed that the plasma-exposed surfaces could sit for at least 8 hours at 49°C and 90% relative humidity prior to applying the adhesive with no loss of bond strength. The handheld plasma tool is safe, easy to use, environmentally friendly, and well suited for treating large, 3-dimensional PEEK panels.
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