Effect of proton and ion beam treatment on cyclic olefin copolymer parts prepared via injection molding
Graphical abstract
Introduction
Plastic parts are currently being employed for a wide range of applications such as automobile, electronics, biology, and medical fields since they possess practically very attractive strong points such as high moldability, versatility, low cost and high production rate [[1], [2], [3]]. Compared with other materials, plastic materials have a relatively short service life in products due to their poor mechanical, thermal and chemical properties [4,5]. For instance, when polymeric parts are used as an electric insulator for fusion reactors, the damage to polymer induced by neutrons and/or ions is a must-resolve problem [[6], [7], [8]].
Ion irradiation can modify and improve the properties of materials by implanting ions such as proton, argon, nitrogen, and metals [[9], [10], [11]]. It is a very efficient way for changing the microstructure of target materials in the advanced material science and engineering [3,12]. Ion beam treatment on plastics is widely utilized due to its effectiveness, environmental friendliness, and facile access. Depending on the energy power, fluence, and profile of ions, ion beam deposits energy inside the target material. Ion bombardment in general causes an irreversible change of surface properties due to the following two mechanisms: one is the momentum transfer to target atoms, and the other is the electronic excitement of target material. These mechanisms are also called the nuclear stopping and electronic stopping [[13], [14], [15]]. In particular, polymers can interact with ion at relatively low energy irradiation and experience chain scission, formation of free radical, carbonization, and cross-linking, leading to significant changes in molecular weight, polymer phase, crystallinity, and so on [12,16,17]. However, the microstructural change of materials induced by ion beam implantation is not fully understood to develop high performance products [[18], [19], [20]].
Cyclic olefin copolymer (COC), an amorphous engineering polymer is used in various applications such as display, optics, healthcare, and microelectronics due to its good mechanical properties, high moisture barrier, and excellent optical properties including exceptional transparency [21,22]. For instance, it is currently being employed as a polymeric substrate material for light guide panel (LGP), which requires good flowability, mechanical properties and dimensional stability. On the other hand, the usage of COC is enlarged by improving its surface properties.
In this study, we investigated the influence of proton and ion beam irradiation on injection molded plastic parts. A light guide panel (LGP) was designed and fabricated with use of injection molding. The chemical and physical properties of the COC panels were analyzed after implanting proton and ion beam to the plastic substrate. To the best of our knowledge, this is the first report regarding the change in the physico-chemical properties of COC after proton and ion implantation. The manufacturing process of the specimen was numerically simulated using finite element method. The residual stress and hardness of the samples were measured and evaluated experimentally.
Section snippets
Experimental
COC was purchased from TOPAS advanced polymers (USA) and used for injection molding. The polymer pellets with a diameter of approximately 1 mm were completely dried 70 °C for 5 h before the injection molding. During the melting process of the pellets, the cylinder and nozzle temperature of the injection molding equipment was set to 330 °C, which is high enough to melt the COC. The mold wall temperature was varied in the range from 110 °C to 135 °C, which was measured directly using a
Numerical simulation
Finite element method was employed to model the injection molding of the plastic parts. The continuity, the momentum, and the energy equations were considered in the numerical calculation as below:where ρ indicates the density, the velocity vector, P the pressure, the viscous stress tensor, the gravity/body-force vector, the specific heat at constant pressure, β the coefficient of thermal expansion, η the so-called generalized
Results and discussion
Fig. 1 presents the photograph of the part fabricated using injection molding. Ion implantation can induce changes in chemical structures of COC, including chain scission, free radical formation, and cross-linking. At the same time, gases and low molecular weight species may be eliminated, and amorphous carbon layer can be formed on the surface. Ion beams can collide with carbon and hydrogen atoms and recoil. In order to predict the penetration depth of proton and nitrogen ion beams, the
Conclusions
In this paper, we studied the effect of proton and ion beam treatment on the injection molded parts. To do this, an LGP was designed and prepared via injection molding. The changes in the chemical and physical properties of the COC panel were investigated after the ion beam irradiation. The penetration depths of the ion beams into the samples were calculated with use of the SRIM code. The injection molding process was numerically simulated to help understand the manufacturing process of the
Acknowledgements
This research was supported by the research fund of Dankook University in 2018 and by the Basic Research Program (2018R1D1A1A09084192) of the National Research Foundation (NRF) funded by the Ministry of Education, Science and Technology, Korea. The authors also acknowledge the support from the Soft Chemical Materials Research Center for Organic-Inorganic Multi-dimensional Structures, which is funded by the Gyeonggi Regional Research Center Program (GRRC dankook 2016-B03).
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