Kinetic analysis of the degradation of HDPE+PP polymer mixtures

Abstract

An in depth understanding of the kinetics of the decomposition of plastic mixtures is necessary to enhance chemical recycling approaches, in particular by pyrolysis. The fact that plastic waste is usually composed of mixtures of plastics constitutes a hindrance for secondary recycling but may not be a particular difficulty for tertiary recycling. In this study, an analysis of the thermal degradation of mixtures of high‐density polyethylene (HDPE) and polypropylene (PP), in different proportions, was carried‐out under pyrolysis conditions using thermogravimetric analysis (TGA) under nonisothermal conditions, at different heating rates. Both isoconversional and model‐fitting approaches were used to estimate kinetic parameters from the experimental information. It was found that both the degradation of HDPE and PP, as well as their mixtures, can be described by a single‐step degradation process but that the degradation process is influenced by the proportion between the two plastics. The HDPE/PP mixtures in which PP has a higher ratio than HDPE cause the degradation onset temperature for the mixture to be lower than either pure PP or pure HDPE. Also, it was found that the apparent activation energy estimated was lower for these mixtures in comparison with the pure polymers. This implies that there are extensive interactions between the plastics during the degradation procedure and, from an operational point of view, it may be actually easier to degrade plastic mixtures than the corresponding pure streams, a conclusion that is important in the context of tertiary recycling of plastic mixtures. Furthermore, it was observed that a compensation effect exists that encompasses all the kinetic data for the mixtures, regardless of the composition, indicating that, although significant changes occur in relation to the activation energy, the underlying degradation mechanism remains the same.

Valorization of Cork and High-Density Polyethylene and Polypropylene Wastes in Cork–Plastic Composites: Their Morphology, Mechanical Performance, and Fire Properties

“…PP r , therefore, degrades at lower temperatures than HDPE r . These results are in agreement with the literature [51][52][53][54]. For PP r , the peak of the MLR occurs at 391 (±6) • C and reaches 4.45 (±0.02) × 10 −3 s −1 .…”

Kinetic Analysis of Thermal Degradation of Recycled Polypropylene and Polystyrene Mixtures Using Regenerated Catalyst from Fluidized Catalytic Cracking Process (FCC)

“…In the Miura-Maki integral method, the approximation of the temperature integral is the same as that used in the KAS method, Equation (12). To derive the Miura-Maki integral method, it is assumed that the activation energy model is distributable to approximate the right-hand side of Equation (13).…”

“…The kinetic study from recycled plastic waste has been carried out by thermogravimetric analysis (TGA) to obtain mass loss data of the mixed plastic waste with respect to time and temperature. It was performed following the procedure described by Briceno et al [12] with some modifications. Thus, 25 mg sample (25% PP and 75% PS) with the addition of 10% regenerated catalyst was fed in the METTLER TOLEDO brand TGA-1 (Quito, Ecuador) thermobalance with a precision of ±0.1 mg using three heating rates (5, 10 and 15 K min −1 ) with nitrogen injection at a constant flow of 20 mL min −1 , heating from room temperature to 1023 K. For data validation, the temperature profiles of each test were performed for triplicate, and these results were corroborated from the first derivate DTG curves.…”

“…Moreover, polystyrene (PS) is one of the most difficult plastics to recycle due to its lower thermal stability with an activation energy value of around 140 kJ mol −1 [10,11]. However, studies of the behavior of plastic mixtures are more limited, PE and PP mixtures being the most studied at different rates and different compositions, where minimum amounts of PP generate a decrease in the activation energy and in the maximum degradation temperature both for HDPE and LDPE, which is due to the synergy effect of the mixture influenced mainly by the lower thermal stability of PP in these composites [12,13]. In addition, Dubdub et al [14] show the behavior of different plastics and their mixtures where the data obtained are adjusted to a single stage of thermal degradation, and the pyrolysis of pure plastic waste occurs in the order PS < PP < LDPE < HDP, while specific mixtures of PP and PS (50/50, wt%) present lower degradation with activation energy values between 144 and 188 kJ mol −1 [15].…”

Multi-Scale Modeling of Plastic Waste Gasification: Opportunities and Challenges

“…Regarding the first, the synergistic effect of the plastic mixture is a fact that has been proved previously [29] and is difficult to be addressed in a kinetic model. According to Briceno et al [159], the apparent activation energy of the degradation for a mixture of PP and HDPE is lower than the pure HDPE, and for the mixture with high content of PP and HDPE, is lower than the pure PP. Predicting the interaction between different polymers is not an easy task, since it is a function of different parameters, such as the reactivity of their intermediate products, the similarity of the polymer types to each other, the concentration of each component, and their mixing degree [160].…”