*3.4. Effect of Processing Parameters through 3 Grades*

Figures 2–11 show the impact of process conditions on color output over all three grades in terms of CIE dE\* values, as created by Design-Expert® L\*, a\*, and b\* represents CIE tristimulus data, related graphics were also created. However, because dE\* takes precedence in this paper, the figures for these tristimulus values are limited. A common occurrence for the grades responsible for the reddest pigment modifications, a design of the experiment was carried out. The goal of the tests was to figure out what processing and material characteristics were producing color discrepancies. The color difference and the processing factors were explored for correlations. With Design-Expert®, general trends were charted, and trials were carried out and statistically analyzed. The experiment was designed with temperature, speed, and flow rate are three processing conditions for a total of 45 runs; these runs were done in three grades (1, 2, and 3) for one parameter while keeping the other two constants, as shown in Table 2.

Five levels were employed to conduct experiments on these three parameters. For example, temperatures reached 230, 240, 255, 270, and 280 ◦C. For each grade and level, values for the four responses (L\*, a\*, b\*, and dE\*) were taken from three different coupons and three different positions on each of these coupons. Figures 1–9 show the variation in color output for grades 1, 2, and 3 as a function of the three processing settings.

**Figure 2.** Temperature effects on dE\* for Grade 1, Grade 2 and Grade 3.

**Figure 3.** Effect of screw speed on dE\* for Grade 1, Grade 2 and Grade 3.

**Figure 5.** Effect of processing parameters on grade 3, L\*.

**Figure 7.** Effect of feed rate on dE\* for Grade 1, Grade 2 and Grade 3.

**Figure 9.** Tristimulus versus feed rate on grade 3.

**Figure 10.** Cube desirability between grade 3 and dE\*.

**Figure 11.** Interaction and overlay plot at 750 rpm.

#### *3.5. Effect of Temperature on dE\**

Figure 2 depicts the fluctuation in dE\* about temperature, demonstrating that color output deviation increases somewhat for grades 1 and 3. However, at 280 ◦C (level five), it became more prominent for both classes—because of the high temperature causing some breakdown in the formulation's resin or additives. When comparing grade 2 to the previous grades, the color output divergence increased dramatically.

#### *3.6. Screw Speed Effect on dE\**

Figure 3 shows that at 775 and 800 rpm, the responses of grades 1, 2, and 3 to screw speed change are very comparable. This appears to be responsive to screw speed changes due to a higher shear rate, which increases pigment particle dispersion in the extruded material. It is also worth noting that for grade 1, level three had the lowest dE\* value. For the three grades, color output begins to improve above 775 rpm. Furthermore, the color output divergence increases dramatically when comparing grade 2 to grades 1 and 3. The shear rate has the same effect on grade 2 as it does on grades 1 and 3.

#### *3.7. Feed Rate Effect on Color*

Similarly, Figure 4 illustrates the fluctuation in dE\* as a function of feed rate. Grades 1, 2, and 3 showed a similar trend to temperature and speed fluctuation (Figures 1 and 2). The feed rate varied between 20 and 30 kg/h. for levels one and five, all three grades demonstrated slight variances from the optimum color output. This could be attributed to a rise in the shear rate at both the maximum and lowest feed rates. In the compounding mixer, this improves the flowability and dispersion of pigments. Furthermore, it shows how they may have a lowering of dE\* values differ depending on the feed rate. This could be related to enhanced pigment dispersion, as higher feed rates cause stronger shear, which leads to better pigment dispersion [37,38].

#### *3.8. Interactions Effect of L\* Values*

The interactions between L\* and the processing parameters are depicted in Figure 5**.** All other parameters were fixed, while each was adjusted to five different levels. Only the interactions for L\* are shown for the sake of brevity. Figure 5 shows that variations in processing circumstances impact L\* values almost like they affect dE\* values. A similar trend variation was seen (L1, L2, L3, L4, and L5).

However, the L\* values for L3 showed the slightest variance and the same value for the three processing parameters for the target color output, especially for grade 3.

Furthermore, Figure 5 depicts the relationship between processing conditions and (L\*) in distinct ways.

Increasing the temperature and weight percentage of PC1 with (higher melt flow index) showed a significant effect in lower viscosity value and decreased color matching values (dE\* ). The formulation and processes effectively controlled the viscosity, and microtomed plastic sections performed characterizing to different thicknesses and temperatures. The optimal number of particles was increased at higher temperatures and thickness [39]. Characterization of polycarbonate formulation at different temperatures was also analyzed. They were rheologically characterized using the rotational rheometer [40].

#### *3.9. Effect of Grades on dE\**

Figure 6 shows that dE\* values for grades 1 and 2 were greater than those for grade 3. This could be because grade 3 used fewer pigments and had better pigment dispersion than grades 1 and 2.

#### *3.10. Grades and Feed Rate Interactions*

Figure 7 shows the effect of feed rate on color output across the three grades (when screw speed is 750 rpm and temperature is 255 ◦C). Figure 7 and Table 7 show that feed rate appears to have the most significant impact on dE\* for all three grades. This can be seen at both low and high feed rates, and it could be due to better dispersion.


**Table 7.** Optimum processing values for color output.

In addition, Table 7 confirms the optimum processing readings for the three grades. The optimum color values are for grade 3 and grade 1.

#### *3.11. Effect on b\* Values*

Figure 8 shows that grades 2 and 3 to b\* change responses were comparable. In their formulas, both grades had the same amount of pigment. As a result, this emphasizes the need for having the same pigment composition and the precision of minute pigment loading. It is provided to demonstrate how minor modifications in a formulation can result in major color variations, leading to lot rejection. More precise measurements should be adopted when weighing any pigment amount, especially when working with sensitive formulations. An in-depth study and understanding of pigment interactions can improve first-pass color production [41,42].

This paper aimed to evaluate the influence of various processing parameters on the dispersion quality of polycarbonate compounds. In addition, the influences of parameters, pigment size distribution, and morphology on the pigment dispersion were also studied [43].

This study reviews the impact of scanning microscopic methods to evaluate the influence of various processing parameters on the dispersion quality of the polycarbonate compound. Experimental data were compared with historical data records [44]. Figure 9 indicates that the feed rate increased the tristimulus color values of dL\*, da\*, db\*, and dE\* for grade 3. It indicates the federate has a significant response on color output.

#### *3.12. Desirability and Overlay Plots*

The following figures show the desirability and overlay plot between processing parameters and grades. Figure 10 is a 3-D view of the predicted desirability for the interaction of processing parameters in terms of dE\* = 0.478. It can be created for each optimal discovery.

Figure 11 illustrates the overlay plot between temperature and feed rate, while screw speed was constant at 750 rpm. In the factor space, the graphical optimization showed the area of possible response values. The yellow region represents the area that meets the required target value, while the gray area represents the area that does not. The points represent the optimum L\*, a\*, b\*, and dE\* values for the grades under consideration. The optima occur at 225 ◦C, 750 rpm, and 29 kg/h, achieving the optimum average value of dE\* (0.68) for all grades.

#### **4. Conclusions**

The current study reveals that different grades respond differently to the desired color output under operating conditions. It is also clear that grade 3 had the best color output value. This could be due to the decreased number of pigments utilized in grade 3's material formulation and, hence, better dispersion of these pigments than in grades 1 or 2. As a result, grade 3 had the lowest MFR readings. A high MFR causes a decrease in viscosity, ultimately breaking the bonds and increasing the flowability of the mixing material.

The impacts of processing factors on color outputs of various grades were investigated, and statistical analysis was used to find correlations between the inputs and outputs. Experiments using general trends (G.T.) and response surface methods (RSM) based on the design of experiments were used to determine the optimum of extrusion settings and color values (DOE). Color outputs and optimal processing conditions were predicted with predictive models.

Different grades produced different color outputs under the same or similar operating conditions.

Finally, it is evident that the three grades had various formulae, but they all had the same color. The optimal color output values and grades were chosen based on our simulation.

From the ANOVA, the *F*-value implied the model was significant for dE\*. Feed rate seems to have the most significant effect on dE\* of the output color for grade 3. A lowering of dE\* values was observed at higher and lower feed rates. This may be due to better dispersion; at increased feed rates, the higher flow generates higher shear, which was associated with better dispersion of pigments. This, in turn, improves the mixture's homogeneity and effectively improves the dispersion of pigments and the quality of the output color. In many cases, mixing resins is required to produce the desired outcomes. However, different resins have different flow rates. The addition of one resin may increase the viscosity of the masterbatch and must go through a melting stage for testing and controlling the quality of the incoming material, which has a substantial impact on color matching. Further research will identify the best processing parameters for various grades and color formulas, resulting in significant waste reduction and faster delivery times for small numbers and prototypes.

**Author Contributions:** J.A. and R.I. were in charge of the study's design. J.A., R.I. and I.T. performed the statistical analyses, and all authors contributed to the interpretation of the results. The final document, which was drafted by J.A., R.I. and I.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**

