Abstract
The performance of many consumer products suffers due to weak and inconsistent bonds formed to low surface energy polymer materials, such as polyolefin-based high-density polyethylene (HDPE), with adhesives, such as cyanoacrylate. In this letter, we present an industrially relevant means of increasing bond shear strength and consistency through vacuum metallization of chromium thin films and nanorods, using HDPE as a prototype material and cyanoacrylate as a prototype adhesive. For the as received HDPE surfaces, unmodified bond shear strength is shown to be only 0.20 MPa with a standard deviation of 14 %. When Cr metallization layers are added onto the HDPE at thicknesses of 50 nm or less, nanorod-structured coatings outperform continuous films and have a maximum bond shear strength of 0.96 MPa with a standard deviation of 7 %. When the metallization layer is greater than 50 nm thick, continuous films demonstrate greater performance than nanorod coatings and have a maximum shear strength of 1.03 MPa with a standard deviation of 6 %. Further, when the combination of surface roughening with P400 grit sandpaper and metallization is used, 100-nm-thick nanorod coatings show a tenfold increase in shear strength over the baseline, reaching a maximum of 2.03 MPa with a standard deviation of only 3 %. The substantial increase in shear strength through metallization, and the combination of roughening with metallization, may have wide-reaching implications in consumer products which utilize low surface energy plastics.
Highlights
Joining together two surfaces using a polymeric adhesive, such as cyanoacrylate, has been commonplace for decades, but the resulting bonds still suffer from major performance issues [1]
Bonds made with low surface energy polyolefin-based materials, such as high-density polyethylene (HDPE), suffer from insufficient bond strength with a large standard deviation [2, 3]
We note that all adhesive joints failed through delamination or tearing of the HDPE surfaces—adhesion to the stainless steel was maintained in all tests
Summary
Joining together two surfaces using a polymeric adhesive, such as cyanoacrylate, has been commonplace for decades, but the resulting bonds still suffer from major performance issues [1]. Bonds made with low surface energy polyolefin-based materials, such as high-density polyethylene (HDPE), suffer from insufficient bond strength with a large standard deviation [2, 3]. Like in some medical devices, adhesive bonding is the only method that is acceptable due to the high cost of alternative methods and additional constraints like dissimilarity of the materials to be bonded [4, 5]. The combination of adhesives that bond to a wide range of materials, like cyanoacrylate, and low surface energy polymeric materials, like HDPE, are necessitated by the constraints of the design. The low bond strength between these materials derives from the absence of polar groups on the polymer surface and the weak chemical interaction between the polymer and adhesive [6, 7]
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