Infrared welding of cross-linkable polyamide 66

Abstract

Introduction 1.Radiation cross-linking of polyamide 66Radiation cross-linking is a well-known and established technique for enhancing the properties of thermoplastic polymers. Typical radiation sources are gamma rays, electron beams and X-rays [1]. The radiation induced cross-links between the macromolecules lead to improved physical properties and allow a wide range of industrial applications like for example pipes and tubes, hip joint pans, foams, shrinking-fit products or automotive applications [1][2][3]. In 1952, Charlesby described the influence of radiation on the properties of polyethylene for the first time [4,5]. Subsequent investigations extended the knowledge about radiation cross-linking and the possible material range [6]. The process of cross-linking can be divided into two main reactions. High-energy radiation transfers energy to the atoms and results in an ionization or excitation of the atoms during the primary reaction [1,2]. Further reactions lead to the formation of radicals. These radicals enable cross-linking of the polymer in its amorphous region in a secondary reaction [1,2]. Aside from the formation of covalent bonds, degradation, chain scission and oxidation can occur, possibly causing the material properties to deteriorate [1]. The resulting three dimensional covalent networks between the macromolecules results in an increase in the short-term temperature resistance and a rubbery-elastic behavior above the crystallite melting temperature, Figure 1 [ 7,8]. These covalent bonds also influence the melting and crystallization behavior towards lower temperatures [1,3,8,9]. Aside from polyethylene, other polymers, such as polyamide, can be cross-linked by high energy radiation [6]. In order to attain economical radiation exposure rates, cross-linking agents are needed. These polyfunctional monomers, e.g. triallyl isocyanurate (TAIC), allow a cross-linking at lower and economical radiation Abstract. Radiation cross-linking of polyamide 66 with electron beams alters the material's characteristics. This leads to a varied relationship amongst the process, structure, and properties for infrared welding cross-linked polyamide 66. A threedimensional network of covalent bonds results in an impeded melt flow and altered welding characteristics. Compared to non-cross linked polyamide, a changed energy input in the weld during infrared heating and a reduced meltdown can be observed. Such thermal developments and a reduced meltdown affect the resulting weld strengths. Welding factors of almost 60% of base material strengths can be achieved. A clear influence of the heating time on the weld strength can be observed. The scope of this article is to investigate the influence of radiation cross-linking on the material characteristics and, by extension, the resulting processing and welding characteristics. Mechanical and optical investigations serve to highlight the influence of radiation cross-linking on the infrared welding process of polyamide 66.

Thermoplastic Overmolding onto Injection-Molded and In Situ Polymerization-Based Polyamides

“…Also, special technologies are developed which help shape the final parts. Among others, overmolding, special joining techniques [3] and also the development of some special electrical or thermal properties [4] could play a key role in their future development.…”