EFFECTS OF SMALL RANGE COLOR (PIGMENT) CONCENTRATION LEVELS IN COMBINATION WITH GAMMA STERILIZATION ON PLASTIC INJECTION MOLDED PARTS

Transcription

1 EFFECTS OF SMALL RANGE COLOR (PIGMENT) CONCENTRATION LEVELS IN COMBINATION WITH GAMMA STERILIZATION ON PLASTIC INJECTION MOLDED PARTS Trivikrama Bhanoji Pala, Mechanical Engineering, New Jersey Institute of Technology, Newark, NJ, I. Joga Rao, Mechanical Engineering, New Jersey Institute of Technology, Newark. NJ. Abstract Color (pigment) concentration levels play a significant role in changing the mechanical properties of an injection molded part. Higher concentration levels could result in functional failure of the parts [1]. A general rule of thumb, concentration levels between 3-5% or 5-10% are being used across different industries to achieve the required color. The above concentration levels are considered as small range concentration levels in this manuscript. Effects of sterilization (radiation) plays an important role on the plastic injection molded parts. The combination of gamma radiation sterilization and color concentration is very useful to the medical devices and food processing Industry. An experimental study is conducted to find out the effects of both small range color concentration and gamma radiation sterilization on the mechanical properties such as tensile strength, strain at yield and break on the Injection molded parts. In this study, Injection molded specimen made up of (polypropylene) and Acrylonitrile Butadiene Styrene (ABS) which are exposed to gamma sterilization of 25 kgy (kilo gray) dose are considered as it common normal dose used for plastics [8]. Depending upon the specific polymer and additives involved. There is no impact on tensile strength, while the strain at yield and at break shown an considerable with increase in the percentage of pigments in case of (polypropylene). There is no trending observed in case of ABS resin. Outcomes may influence performance and should be evaluated in advance by functional testing. Hence product designers may need to assess the impact of these small pigment concentration levels in combination with the sterilization effect with respect to the base resin and need to specify the acceptable pigment concentration levels in combination with sterilization in their product drawings or in product specification documents. Introduction In the present medical device Industry there is demand for using plastic with lot of color concentration in combination with sterilization. Pigments are generally colored, organic or inorganic solid powder, and usually are insoluble. They are not affected physically or chemically in the substrate in which they are incorporated. Pigments can give a full range of colors. The pigments are versatile coloring agents that come with all round features to give credence to its suitability in a variety of mediums. Generally plastics are processed by injection molding, extrusion, blow molding, thermoforming, rotational molding, foam processes, and calendaring. Effects of colorants during injection molding can be seen on mold shrinkage, cycle time, mixing, and crystallization temperature. As per the requirements of the product design, various color concentrations are added to the base resin during the injection molding process. This colorant can be added in two ways: a) hand-mixing the resin before molding b) by screw compounding automatically by hopper loader. In Medical device industry single-use disposable technologies have been used in medical devices industry the 1970s on a limited scale. It is only since the 21st century that such technologies are being implemented for large-scale manufacturing (e.g., upstream, downstream, and product filling applications). The forces driving the wider adoption include improving or eliminating cross contamination, sterility assurance, process efficiencies, operator protection, and cost savings. Single-use disposable technologies are generally manufactured from plastic polymers involving processes of injection molding, extruding, and blow molding. The applications include devices for making aseptic connections, sampling devices, mixing devices, product-hold bags, and disposable manifold systems. Each of these systems is used to process or contain fluids including additives, buffers, bulk intermediates, and final formulations [8]. In food packaging industry, due to the extremely wide variability of irradiated foods, indirect effects on their packaging have to be established for each particular product and package. In turn, the direct effect of irradiation may be predicted to some extent. Although general guidelines may be drawn, each material must be investigated very carefully for each specific application [6]. Sterilization is a term referring to any process that eliminates or kills all forms of life and other biological agents. Sterilization can be achieved with one or more of the following: heat, chemicals, irradiation, high pressure, and filtration. Sterilization is distinct from disinfection, sanitization, and pasteurization in that sterilization kills, deactivates, or eliminates all forms of life and other biological agents. Sterilization can be achieved using electromagnetic radiation such as electron beams, X-rays, gamma rays, or irradiation by subatomic particles. Electromagnetic or particulate radiation can be energetic enough to ionize atoms or molecules (ionizing radiation), or less energetic (non-ionizing radiation). This study employed gamma radiation. It is very penetrating, and is commonly used for sterilization of disposable medical SPE ANTEC Anaheim 2017 / 2086

2 equipment, syringes, needles, cannulas and IV sets, and food. It is emitted by a radioisotope, usually Cobalt- 60(60Co) or caesium-137 (137Cs). The important variables for gamma radiation are the strength of the radiation dose (i.e., measurement of how much energy is absorbed when something is exposed to the radiation source) and the exposure time. The measurement of radiation is expressed in units called KiloGrays (kgy). One gray is the absorption of one joule of radiation energy by one kilogram of matter. There is also considerable variation with types of plastic. For example, a relatively low dose of radiation is required to sterilize polypropylene when compared with polystyrene. Furthermore, the assessment of the dose is more straightforward for small items, such as a plastic container, and more complex for single-use systems. Considering these factors, a common radiation dose used for plastics is in the range kgy [8]. So, in this study 25 kgy dose of radiation is considered. This study investigate the effect of small color concentrations which are exposed to the gamma sterilization of 25kgy dose on mechanical properties specifically, two base resins are used in this study: Polypropylene () with Melt flow in the range of 20 gram/10min and Acrylonitrile Butadiene Styrene (ABS) with Melt Flow in the range of gram/10 min. The colorant used for and ABS was blue and purple respectively. Early Study Results [2] & [3] Comparison of Mechanical Properties before and after gamma irradiation of with no colorant [3]. Table 3: Summary results for resin with no colorant. Tensile strength Increasing trend Strain at yield Decreasing trend Methods The samples used for this study were injection molded ASTM Type 1 specimen as shown in Figure 1 () and Figure 2 (ABS). Colorants of and ABS are weighed in calibrated weighing machine in the respective ratios of 1%, 2%, 5%, 7% and 10% of base material and were hand mixed in tumbler for 30 minutes. The prepared resin was used to produce injection molded ASTM Type 1 dog bone specimens at respective molding conditions. Five specimen each 1%, 2%, 5%, 7% and 10% of colorants are used for both and ABS resins. So, total of 25 specimens of and 25 specimens of ABS were used in this study. All of these 50 specimens were exposed gamma with 25 kgy (kilo gray) dose. ASTM D Standard Test Method for Tensile properties of plastics were used for tensile testing. Type 1 tensile bars were conditioned to 40ºC and, 50% RH. Following tables shows the summary results of effects of smaller range color (pigment) concentration levels (1%, 2%, 5%, 7% and 10%) on both and ABS resin injection molded parts [2]. Table 1: Summary results for resin with small level of color concentration levels. Base Resin Property Tensile strength Strain at yield Strain at break Comments No trend Increasing Table 2: Summary results for ABS resin with small level of color concentration levels. Base Resin ABS Property Tensile strength Strain at yield Strain at break Comments No trend increasing trend Figure 1: Injection molded base resin with ASTM Type 1 Specifications. Figure 2: Injection molded ABS base resin with ASTM Type 1 Specifications. Results and Discussion Plots below show the variation observed for each mechanical property with respect to color concentrations. If R squared value is > 0.5 at liner trend line, it is considered SPE ANTEC Anaheim 2017 / 2087

3 as partial trending. Figures 3-5 are for resin and Figures 6-8 are for ABS resin Figure 5: Strain at break variation for resin Figure 3: Tensile Strength variation for resin Figure 3 represents resin tensile strength versus colorant R squared value is which is less than 0.5 at liner trend line and hence no trend is observed. Figure 5 represents resin strain at break versus colorant R squared value is and which is greater than 0.5 at liner trend line and hence partially is observed. So, as the % colorant increases strain at break decreases. Figure 4: Strain at yield variation for resin Figure 4 represents resin strain at yield versus colorant R squared value is and which is greater than 0.5 at liner trend line and hence partially is observed. So, as the % colorant increases strain at yield decreases. Figure 6: Tensile strength variation for ABS resin Figure 6 represents ABS resin tensile strength versus It shows R squared value is which is less than 0.5 at liner trend line and hence no trend is observed. SPE ANTEC Anaheim 2017 / 2088

4 Table 4: Summary results for resin Tensile strength No trend Strain at yield Strain at break Table 5: Summary results for ABS resin Figure 7: Strain at yield variation for ABS resin Figure 7 represents ABS resin strain at yield versus It shows R squared value is and which is less than 0.5 at liner trend line and hence no trend is observed. Figure 8: Strain at break variation for ABS resin Figure 8 represents ABS resin strain at break versus It shows R squared value is and which is less than 0.5 at liner trend line and hence no trend is observed. Figures 3 to 6 shows the mechanical properties trends for resin with different concentration levels. Figures 7 to 10 shows the mechanical properties trends for ABS resin with different concentration levels. Tensile strength No trend ABS Strain at yield No trend Strain at break No trend Table 1 and Table to 2 show the summary of results of testing for both and ABS respectively. Conclusions It was found that the effects of small range color concentration resin exposed to 25kGy gamma radiation showed no trend in the tensile strength and showed partially for strain at yield and strain at break. And also found that small range color concentration ABS resin exposed to 25 kgy gamma radiation showed no trend in tensile strength, strain at yield and strain at break. If these change in mechanical properties are important, then the small range color concentration in combination with gamma radiation are useful for product designer during designing a product. Manufacturers should be cognizant of the possible impact and the outcomes may influence performance and should be evaluated in advance by functional testing. Acknowledgement The authors would like to acknowledge the support of Mahesh, Hemanth and Aditya for their support. References 1. Shantanu Shivdekar, Boston Scientific, Understanding the impact of Pigment Loading level on Injection molded components, - SPE ANTEC Trivikrama Pala and Dr. I.J. Rao, Effects of small range color (pigment) concentration levels on plastic injection molded parts, - ANTEC 2016, The Plastic Technology Conference Indianapolis, USA, May Trivikrama Pala and Dr. I.J. Rao, Effects of external process (sterilization) on the plastic injection molded parts, - Proceedings of the SPE ANTEC Anaheim 2017 / 2089

5 2016 International Conference on Polymer Science and Engineering, New Orleans, USA, August Andrew W. Salamon and R. Bruce Cassel, the Perkin Elmer Corporation, Thermogravimetry of Polymers, - SPE ANTEC Myer Ezrin, Gary Lavigne, Mark Dudley, Laura Pinatti and Fiona Leek Retired, Institute of Materials Science, The Role of Analytical and Physical Methods in Plastics Failure Analysis, - SPE ANTEC M. Pentimallia,, D. Capitanib, A. Ferrandoc, D. Ferric, P. Ragnia, A.L. Segreb Gamma irradiation of food packaging materials: an NMR study. 7. Antonios E. Goulasa, Kyriakos A. Riganakosb, MichaelG. Kontominas, Effect of ionizing radiation on physicochemical and mechanical properties of commercial multilayer coextruded flexible plastics packaging materials. 8. Madhu Raju Saghee Application of Sterilization by Gamma Radiation for Single-Use Disposable Technologies in the Biopharmaceutical Sector. SPE ANTEC Anaheim 2017 / 2090