Laser surface texturing for surface preparation of adhesive bonding of polypropylene

Abstract Adhesive bonding is an important joining technique in the industry. However, challenges persist when joining polymers, particularly due to their low surface energy, which impedes adhesion. This study explores the potential of femtosecond laser surface texturing to enhance the adhesive bonding of polypropylene. By modifying surface properties through laser parameters such as power, frequency, and scanning speed, the surface energy of polypropylene increased notably, reaching up to between $$38\;\mathrm{mNm}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>38</mml:mn> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mi>mNm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> and $$44\;\mathrm{mNm}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>44</mml:mn> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mi>mNm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , compared to cleaned-only samples with isopropanol and AP1-CLR at $$&lt;25\;\mathrm{mNm}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>&lt;</mml:mo> <mml:mn>25</mml:mn> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mi>mNm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> but still lower as SACO-Blasting with $$&gt;72\;\mathrm{mNm}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>&gt;</mml:mo> <mml:mn>72</mml:mn> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mi>mNm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> . Two adhesives were analyzed: Acralock PP1-02 (Methyl Methacrylate) and 3M Scotch-Weld DP420NS-Black (epoxy-based adhesive), both of which exhibited increased bonding strength under optimized laser treatment. Additionally, mechanical interlocking effects created by laser structuring contributed to stronger bonds. The methyl methacrylate adhesive also demonstrated improved fracture patterns, showing a shift toward cohesive failure. Despite the promising results, further optimization of laser parameters is required to refine surface characteristics specifically for polypropylene, address variations in bonding performance across different adhesives and enhance the reproducibility of the bonds, to reach the performance of other pretreatments like SACO blasting.