Mixture–Process Design and Multiresponse Optimization of Starch–Gelatin Films Containing Nopal-Opuntia spp. Mucilage: Mechanical Properties and Apparent Mass Loss

The performance of biopolymer films depends on both composition and formation conditions. This study evaluated films containing constant amounts of Nopal-Opuntia spp. mucilage, glycerol, and vinegar using a 16-run mixture–process design with four starch–gelatin ratios and post-drying thermal-treatment settings of 40 or 60 °C for 5 or 10 min. Maximum tensile stress, a provisional modulus, elongation, and apparent mass loss in soil and outdoors were analyzed over 48 days. Model adequacy was assessed using fit statistics, leave-one-formulation-out predictions, and influence diagnostics. The primary multiresponse solution assigned lower relative importance to the two gravimetric responses than to the three mechanical responses and corresponded to starch/gelatin 0.25/0.75 at 40 °C for 5 min (D = 0.644), coinciding with observed run F04. Equal-response and gravimetric-loss-emphasis solutions were retained as sensitivity analyses; their intermediate times are unconfirmed model interpolations. F04 showed the highest observed stress (1.614 MPa) and provisional modulus (24.358 MPa), F16 the greatest elongation (99.269%), and F09 the greatest observed apparent mass loss (93.0% in soil and 95.0% outdoors). One film was manufactured per run, the starting mass used for gravimetric calculations was nominal, and no confirmatory runs were conducted. Accordingly, the estimates remain formulation-specific and exploratory; mass loss does not demonstrate biodegradation.