# Efficient Approach for Direct Robust Surface Grafting of Polyethyleneimine onto a Polyester Surface during Moulding

## TL;DR

The paper presents a method to modify polyester surfaces during molding by grafting polyethyleneimine, resulting in stable and durable surface properties.

## Contribution

A novel and efficient surface grafting method for polyester during molding is introduced, enabling stable amide bond formation and controllable surface modification.

## Key findings

- XPS analysis showed high conversion and even distribution of amino groups on the polyester surface.
- The grafted polyethyleneimine layer resisted multiple cycles of alkaline extraction.
- Surface modification effectiveness was influenced by the molar mass of polyethyleneimine.

## Abstract

This paper uses a very effective way for surface modification of thermoplastic polymers during moulding. It is based on a grafting reaction between a thin layer of a functional polymer, deposited on a substrate in advance, and a polymer melt. In this paper, a glycol-modified polyethylene terephthalate (PETG) that was brought in contact with a polyethyleneimine layer during fused filament fabrication is investigated. The focus of this paper is the investigation of the reaction product. Grafting was realised by the formation of stable amide bonds by amidation of ester groups in the main chain of a PETG. XPS investigations revealed that the conversion of amino groups was very high, the distribution was even, and the quantity of amino groups per polyester surface area was still very high. The surface properties of the produced polyester part were mainly characterised by polyethyleneimine. The grafting was able to resist several cycles of extraction in alkaline solutions. The stability was only limited by saponification of the polyester. The degree of surface modification was dependent on the molar mass of polyethyleneimine. This could be rationalised, because grafting only occurred with the one polyethyleneimine molecule that is in close vicinity to the polyester surface when both components come in contact. Fused deposition modelling was chosen as the model process with control over each processing step. However, any other moulding process may be applied, particularly injection moulding for mass production.