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High-density polyethylene (HDPE) and polypropylene (PP) blends are widely used in industries requiring mechanically durable materials, yet the impact of processing parameters on blend performance remains underexplored. This study investigates the influence of blending sequence and screw speed on the properties of blends of HDPE and PP filled with 1.25 wt.% graphene nanoplatelets (GNPs). Changes in crystallization behaviour, tensile strength, and viscoelastic responses with blending sequence are studied. The addition of GNP increases the crystallization temperature (Tc) of PP in the PE/PP blend by 4 °C when GNP is pre-mixed with PE to form (PE+GNP)/PP blends. In contrast, when GNP is pre-mixed with PP to create (PP+GNP)/PE blends, the Tc of PP rises by approximately 11 °C, from 124 °C for the neat PE/PP blend to 135 °C. On the other hand, the Tc of PE remains unchanged regardless of the blending sequence. XRD patterns reveal the impact of blending regime on crystallinity, with GNP alignment affecting peak intensities confirming the more efficient interaction of GNPs with PP when premixed before blending with PE, (PP+GNP)/PE. Tensile moduli are less sensitive to the changes in processing, e.g., screw speed and blending sequence. In contrast, elongation at break and tensile toughness show distinct variations. The elongation at the break of the (PP+GNP)/PE blend decreases by 30% on increasing screw speed from 50 to 200 rpm. Moreover, the elongation at the break of (PE+GNP)/PP prepared at 100 rpm is ~40% higher than that of the (PP+GNP)/PE. (PE+GNP)/PP displays a 'quasi-co-continuous' morphology linked to its higher elastic modulus G′ compared to that of the (PP+GNP)/PE blend. This study highlights the importance and correlation between processing and blend properties, offering insights into fine-tuning polymer composite formulation for optimal performance. [ABSTRACT FROM AUTHOR]

In this work, the effects of blend ratio and mixing time on the migration of multi-walled carbon nanotubes (MWCNTs) within poly(vinylidene fluoride) (PVDF)/polyethylene (PE) blends are studied. A novel two-step mixing approach was used to pre-localize MWCNTs within the PE phase, and subsequently allow them to migrate into the thermodynamically favored PVDF phase. Light microscopy images confirm that MWCNTs migrate from PE to PVDF, and transmission electron microscopy (TEM) images show individual MWCNTs migrating fully into PVDF, while agglomerates remained trapped at the PVDF/PE interface. PVDF:PE 50:50 and 20:80 polymer blend nanocomposites with 2 vol% MWCNTs exhibit exceptional electromagnetic interference shielding effectiveness (EMI SE) at 10 min of mixing (13 and 16 dB, respectively-at a thickness of 0.45 mm), when compared to 30 s of mixing (11 and 12 dB, respectively), suggesting the formation of more interconnected MWCNT networks over time. TEM images show that these improved microstructures are concentrated on the PE side of the PVDF/PE interface. A modified version of the "Slim-Fast-Mechanism" is proposed to explain the migration behavior of MWCNTs within the PVDF/PE blend. In this theory, MWCNTs approaching perpendicular to the interface penetrate the PVDF/PE interface, while those approaching in parallel or as MWCNT agglomerates remain trapped. Trapped MWCNTs act as barriers to additional MWCNTs, regardless of geometry. This mechanism is verified via TEM and scanning electron microscopy and suggests the feasibility of localizing MWCNTs at the interface of PVDF/PE blends. [ABSTRACT FROM AUTHOR]

Since the first publications of large amplitude oscillatory shear (LAOS) responses of polymeric materials in the 1960s, different approaches have been developed to express, analyze, and interpret nonlinear viscoelastic behavior of materials. LAOS is currently recognized as one of the most powerful rheological techniques to characterize nonlinear viscoelasticity, as the amplitude and frequency of the employed deformation can be controlled, allowing researchers to tune the strength of flow and time scale independently. Additionally, in contrast to small amplitude oscillatory shear (SAOS) flow, LAOS is not limited to a perturbation about equilibrium. Such flexibility makes LAOS an attractive rheological protocol to mimic numerous industrial applications. Recently, there has been significant progress in the LAOS characterization of polymeric materials via different analysis techniques, including Fourier transform rheology, stress decomposition, Chebyshev coefficients, sequence of physical processes, and intrinsic nonlinearity. These advances have been achieved through utilization of modern commercial rheometers with high torque resolution and strong computational power, making the exploitation of these techniques possible in the recent decade. This increased accessibility has seen the number of LAOS publications dramatically increase in the past few years. The current surge in interest in the use of LAOS tests necessitates the search for appropriate measurement techniques to probe the nonlinear response of complex fluids. Although this area has been significantly investigated by many researchers who measured and reported LAOS data from a wide range of rheologically-complex materials, there is still one question that needs to be answered: which method of LAOS analysis is best for a specific polymeric system? In fact, the high volume of publications in the past decade provides us a unique opportunity for such a query to validate the efforts on the LAOS developments and compare the utility and sensitivity of these protocols. In this review, we highlight the history and fundamentals of each technique in chronological order. We present parameters and equations of each method that are indispensable for LAOS interpretation. We also present experimental work in LAOS characterization of polymeric materials, classified into four categories: (1) polymer solutions and melts, (2) polymer nanocomposites, (3) polymer blends, and (4) hydrogels. Indeed, the raison d'être of this review paper is that the nonlinear rheological properties of the mentioned polymeric systems are very sensitive to their microstructural features. In each section, the challenges and perspectives will be discussed to enhance understanding of the performance level of each method. This review offers inspiration for the interpretation of LAOS data to help rheologists and newcomers, and to contribute to current and future developments in the field. [Display omitted] [ABSTRACT FROM AUTHOR]