Table 2.

Different levels of fillers mixed with Flexibond.

Code	Parameters	Level -2	Level -1	Level 0	Level 1	Level 2
A	WRPU (wt%)	6	12	18	24	30
B	WPCB (wt%)	2	4	6	8	10
C	RTW (wt%)	3	6	9	12	15

Note: Based on preliminary manufacturing trials and literature values, specific ranges of WRPU (6–30 wt%), WPCB (2–10 wt%), and RTW (3–15 wt%) were chosen. Below these concentrations, the WRPU, WPCB, and RTW reinforcement materials were not sufficiently bonded together, and above these concentrations the samples compromised processability and integrity. The coding system has five levels from − 2 to + 2 as noted in Table 2, which indicates the minimum to maximum workable values for these range values.