# Benchmarking adhesive performance in bonding FDM TPU to PBF PA12 3D-printed parts

## TL;DR

This paper compares different adhesives for bonding flexible TPU to rigid PA12 3D-printed parts and finds Loctite 401 with 770 primer to be the most effective.

## Contribution

The study benchmarks five adhesives for TPU-PA12 bonding without pretreatment, identifying Loctite 401 + 770 as the most reliable option.

## Key findings

- Loctite 401 + 770 achieved highest mean strengths in peel, shear, and tensile tests with low variability.
- DP8010 and Mannol underperformed compared to other adhesives, especially in peel and tensile testing.
- Cohesive failures were predominant, suggesting adhesive failure rather than substrate failure.

## Abstract

Additive manufacturing provides an efficient method to rapidly develop prototypes utilizing TPU, which is flexible, and Nylon (PA12), which is known for strength and chemical resistance. Five structural adhesives to bond, without plasma/flame pretreatments, flexible FDM TPU to rigid PBF PA12 were benchmarked using the ASTM D903 (180° peel), D2095 (butt-joint tensile), and D3163/D3164 (lap-shear) standards. The adhesives tested were Loctite HY4070, Permatex Plastic Welder, Mannol 9904, Loctite 401 with 770 primer, and 3M DP8010. Across five samples per test, Loctite 401 + 770 achieved the highest mean strengths with low scatter (COV ≤ 15%) in peel (2.6 N/mm), shear (3.0 MPa), and tensile (2.7 MPa) testing. Occasional adherend-side failures in shear suggested joint strengths approaching that of the substrate. The performances of HY4070 and Permatex were acceptable but fell below that of the Loctite 401 + 770. DP8010 and Mannol underperformed, especially in peel and tensile testing. Stress–displacement curves and failure-surface images suggest these adhesives predominantly experienced cohesive failures. Adhesive TPU-PA12 bonding using Loctite 401 with 770 primer is a robust, simple, and fast assembly approach when the presence of thin bond lines is acceptable. We minimize variability through defined process controls and, for durability-critical products, recommend next-stage tests: aging, impact, UV, and fatigue.