The Modification of Useful Injection-Molded Parts' Properties Induced Using High-Energy Radiation

Abstract

The modification of polymer materials' useful properties can be applicable in many industrial areas due to the ability to make commodity and technical plastics (plastics that offer many benefits, such as processability, by injection molding) useful in more demanding applications. In the case of injection-molded parts, one of the most suitable methods for modification appears to be high-energy irradiation, which is currently used primarily for the modification of mechanical and thermal properties. However, well-chosen doses can effectively modify the properties of the surface layer as well. The purpose of this study is to provide a complex description of high-energy radiation's (β radiation) influence on the useful properties of injection-molded parts made from common polymers. The results indicate that β radiation initiates the cross-linking process in material and leads to improved mechanical properties. Besides the cross-linking process, the material also experiences oxidation, which influences the properties of the surface layer. Based on the measured results, the main outputs of this study are appropriately designed regression models that determine the optimal dose of radiation.

Keywords: beta radiation; cross-linking; injection molding; mechanical properties; oxidation; polymers; regression; surface properties.

Figure 1

Droplet profile analysis: θ—wetting contact angle; h—droplet height, r_b—droplet radius at contact point; and R—entire droplet radius [5,40].

Figure 2

Bonded joint (dimensions in mm): (1) adhesive layer; (2) area of test machine grips; (3) shear area [39,40].

Figure 3

Proposed regression models–the effect of radiation dose on surface and adhesion properties: (aI) HDPE, free surface energy; (aII) HDPE, load-bearing of adhered joints; (bI) PA66, free surface energy; (bII) PA66, load-bearing of adhered joints.

Figure 4

The bonded surface for HDPE after shear strength test: (a) Image of original surface; (b) image of surface modified by β radiation; (c) topography of non-modified surface; (d) topography of surface modified by β radiation.

Figure 5

The bonded surface for PA66 after shear strength test: (a) Image of original surface; (b) image of surface modified by β radiation; (c) topography of non-modified surface; (d) topography of surface modified by β radiation.

Figure 6

The infrared spectra: (a) HDPE, untreated; (b) HDPE, after β radiation treatment.

Figure 7

The infrared spectra: (a) PA66, untreated; (b) PA66, after βradiation treatment.

Figure 8

Mechanical properties of HDPE: (a) spatial portrayal of regression models (tensile strength); (b) spatial description of regression models (bending strength); (c) responsive area (tensile strength); (d) responsive area (bending strength).

Figure 8

Mechanical properties of HDPE: (a) spatial portrayal of regression models (tensile strength); (b) spatial description of regression models (bending strength); (c) responsive area (tensile strength); (d) responsive area (bending strength).

Figure 9

Mechanical properties of PA66: (a) spatial portrayal of regression models (tensile strength); (b) spatial description of regression models (bending strength); (c) responsive area (tensile strength); (d) responsive area (bending strength).

Figure 10

The dependence of bending stress on deformation: (a) HDPE; (b) PA66.

Figure 11

The effect of radiation on gel content: (a) PA66; (b) HDPE.

Figure 12

The optimal dose for HDPE: (a) tensile strength/free surface energy; (b) bending strength/free surface energy; (c) tensile strength/load-bearing of adhered joints; (d) bending strength/load-bearing of adhered joints.

Figure 13

The optimal dose for PA66: (a) tensile strength/free surface energy; (b) bending strength/free surface energy; (c) tensile strength/load-bearing of adhered joints; (d) bending strength/load-bearing of adhered joints.