Preparation Process Orthogonal Optimization and Mechanical Properties of Microcellular Foam Polypropylene

Abstract

Melt strength, pressure and the amount of gas have significant effects on the foaming of polypropylene (PP). It is convenient to study the influence of these factors on foaming effect by orthogonal test. The experiment result shows that within the set factors and levels, the improvement of melt and the concentration of foaming masterbatch has the greatest influence on the cell size and density of foamed PP, respectively. When the concentration of azodicarbonamide (ADC) is 15 %, PP/ethylene‐propylene terpolymer (EPDM) = 90:10, and SiO2 content is 3%, the foaming effect is the best. At this time, the cell diameter decreases by 42.7%, cell density increases by more than 7.5 times compared with that without optimization. Material density decreases from 0.92 to 0.56 g cm−3. It is also found that good closed‐cell structure can improve the bending and impact properties of PP in varying degrees, especially the impact strength is 55.7% higher than that of neat PP. Finally, the promoting mechanism of cell structure on mechanical properties of materials is discussed, which is of great significance for the preparation of microfoamed PP materials and the deep research of its cell structure.

Foam processability of polypropylene/sisal fiber composites having near‐critical fiber length for acoustic absorption properties

“…Nevertheless, the peak attributed to α* transition in the tan δ curves (Figure 12C), was particularly affected after foaming. The strain‐induced crystallization that occurs during foaming significantly affects the crystallinity, crystal structure, lamellar thickness and grain boundary slip that may have led to the observed change in the α * transition 46 …”

“…In composites, an increase in fiber concentration shows a gradual increase in the glass transition temperature. The presence of fibers restricts the mobility of the amorphous chain segments which leads to an increase in the T g with an increase in fiber concentration 24,46,47 . After foaming, the T g was found to increase further probably because the formation of cells pushes the solid matrix into thin cell walls enhancing the interaction between fibers and polymer molecules.…”

“…The strain-induced crystallization that occurs during foaming significantly affects the crystallinity, crystal structure, lamellar thickness and grain boundary slip that may have led to the observed change in the α* transition. 46 The value of tan δ was found to be independent of fiber concentration in the foamed composites. The T g , however, displays a peculiar behavior after foaming.…”

“…The presence of fibers restricts the mobility of the amorphous chain segments which leads to an increase in the T g with an increase in fiber concentration. 24,46,47 After foaming, the T g was found to increase further probably because the formation of cells pushes the solid matrix into thin cell walls enhancing the interaction between fibers and polymer molecules. The stronger interaction further confines the polymer chains around the fiber and leads to an increase in the T g .…”

Thermochemical Foaming of Mixed Single-Use Plastics Toward Flame Retardant Potential Foams

“…When the POs are foaming in the unmelted state, the crystalline regions seriously affect the diffusion of gas, resulting in less dissolved gas in the polymer matrix, and a significant difference in gas content between the crystalline and amorphous regions. , When foaming is carried out above the melting points of the POs, due to the linear structure of the molecular chains, the melt strength severely decrease. Furthermore, the cell walls with lower melt strength cannot withstand the bidirectional tensile force caused by pore growth, resulting in pore rupture, merging, and escape of foaming gas, which seriously affects the pore morphology and foaming rate. − …”