Dimensional Stability of LDPE Foams with CO₂ + i-C₄H₁₀ Mixtures as Blowing Agent: Experimental and Numerical Simulation

Polyethylene foams, which account for a large share of the total production of thermoplastic foams, are mainly produced through the extrusion foaming process with butane as the blowing agent. Drawbacks exist in terms of the safety hazards of the blowing agent as well as the aging requirement for eliminating residual butane prior to shipping to customers, which usually takes 1–2 weeks and poses significant cost and logistical challenges. Eliminating the safety risks and reducing the aging time are the major challenges facing the industry. In this work, CO2 is used as an inert gas to blend with isobutane (i-C4H10) in the foaming process to dilute the concentration of i-C4H10 and hence eliminate the safety risks. The solubility of pure gas and gas mixtures in low-density polyethylene (LDPE) was measured under experimental foaming conditions, and the diffusivity of pure gas and gas mixture in LDPE was clarified by desorption experiments. Subsequently, the foaming behavior of LDPE with CO2 + i-C4H10 mixtures was studied, and the shrinkage behavior of the LDPE foams was investigated by means of experimental analysis and numerical simulation of dimensional stability. The results showed that unlike the LDPE foams blown with CO2 that present severe shrinkage and poor appearance, the LDPE foams blown with the CO2 + i-C4H10 mixture exhibited much better dimensional stability. Moreover, the addition of more than 36 wt % i-C4H10 to the blowing agent mixture in the foaming experiment could not only facilitate the controllable preparation of cell morphology but also effectively solve the shrinkage problem of LDPE foams.