New Considerations on the Determination of the Apparent Shear Viscosity of Polymer Melt with Micro Capillary Dies

Capillary rheometers have been widely used for the rheological measurement of polymer melts. However, when micro capillary dies are used, the results are usually neither accurate nor consistent, even under the same measurement conditions. In this work, theoretical modeling and experimental studies were conducted for a more profound understanding of the mechanism by which the initial and boundary conditions influence the inaccuracy in the apparent shear viscosity determination with micro capillary dies (diameters: 500 μm, 200 μm, 100 μm). The results indicate that the amount of polymer initially in the barrel, the pre-compaction pressure and the capillary die diameter have a significant influence on the development of the micro scale inlet pressure, which directly determines the accuracy of the measurement at low and medium shear rates. The varying melt compressibility was confirmed to be the main factor directly related to the inaccuracy in the micro scale apparent shear viscosity determination. It is suggested that measures such as reducing the amount of polymer initially in the barrel and increasing the pre-compaction pressure could be used to reduce the measurement inaccuracy.

The influence in difference of compatibilizers on the mechanical and rheological properties of LDPE/PLST blends

In this present study, low density polyethylene/plasticizer starch (LDPE/PLST) blends were prepared as a product to be used in disposable packaging (film applications), reducing the negative polymeric environmental effect. Because of their different molecular structures, LDPE blends with starch are fully immiscible; therefore, a compatibility agent is required. Three different polymer and/or copolymer: poly (vinyl alcohol) hydrolyzed 75% (PVOH), styrene-allyl alcohol copolymer (SAA) and polyethylene glycol (PEG) were selected as compatibilizers containing –OH groups. The effects of compatibilizer on the mechanical and rheological properties of LDPE/PLST blends were investigated and compared to LDPE/PLST without compatibilzer. The blends are also characterized by FTIR, which strongly indicates the existence of compatibilizers that can enhance phase interaction and promote compatibility in the blends of LDPE/PLST. Comparing to the blend without a compatibilizer, the tensile strengths of the blends containing PVOH and SAA increased significantly. The elongation at break results shows similar observation. The rheological measurement results suggested that the addition of a compatibilizer exhibited an increase in the shear stress and apparent viscosity comparing to the uncompatibilized blend except the blend with PEG which exhibited phase separation.

Rheological and mechanical properties of polypropylene/grape skin fiber composites

The use of natural fibers as fillers in polymer matrix composites is an alternative for reusing the fruit wastes that originated from the food industry. This work aimed to evaluate the effect of grape skin fiber (GSF) on the rheological and mechanical properties of polypropylene/GSF (PP/GSF) composites. The composites were prepared by extrusion followed by injection molding and characterized by rheological, morphological, and mechanical properties. Rheological measurement results showed an increase in viscosity at low frequencies. The relaxation time of the PP/GSF composites increased by about 415% with the increase in the GSF content from 1 to 3 phr. Capillary rheometry results indicated that the processability of PP was not compromised with the addition of GSF. Morphology analysis by scanning electron microscopy (SEM) indicated a good interaction between the PP matrix and GSF and a good dispersion/distribution of the fibers in the PP matrix. The impact strength decreased by about 14 and 17% with the addition of 1 and 3 phr, respectively, of GSF to PP whereas the elastic modulus remained almost unchanged.

Rheological Characterization and Modeling of Thermally Unstable Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)

Presently, almost every industry uses conventional plastics. Its production from petroleum and extensive plastic pollution cause environmental problems. More sustainable alternatives to plastics include bioplastics such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which is produced by bacteria and is biodegradable even in seawater. High temperature sensitivity as well as massive thermal degradation cause difficulties during the processing of PHBV. The aim of this work is to create a detailed rheological characterization and master curves to gain deeper knowledge about the material and its processing parameters. The rheological characterization was performed with frequency sweeps in the range of 0.1 rad/s to 628 rad/s and time sweeps over 300 s. Creating master curves at the reference temperature of 180 °C with the software IRIS delivers Carreau and Arrhenius parameters. These parameters allow for a calculation of the master curves for all other temperatures by means of the temperature shift factor. Moreover, the rheological measurements reveal a minimum rheological measurement temperature of 178 °C and a surprisingly high activation energy of 241.8 kJ/mol.

Evaluating the gas-laden ability of polymer melt under atmospheric conditions using a modified torque rheometer

To investigate the effects of incorporating gas and the associated influencing factors on polymer melt, a method of evaluating the gas-laden ability using modified rheometric measurements was proposed. In this study, common and widely used thermoplastic materials—polypropylene (PP) and high-density polyethylene (HDPE), and their blends with different weight ratios—were selected, and the rheological properties of neat melt and gas-laden melts were tested using a modified torque rheometer. The foamed samples were also produced using a regular injection-molding machine, and the foamed morphology was examined by scanning electron microscope (SEM). The comparison of rheological curves of neat melt and gas-laden melt indicated that the incorporation of gas influenced the rheological properties of the gas-laden polymer melts as evidenced by a decrease of zero-rotational torque and an increase in the melt flow index. The results also suggested that the gas-laden ability of polymer melt could be evaluated quantitatively by the decay (due to desorption) of gas using the modified rheological measurement method. This study also demonstrated that the gas-laden ability can be used to predict the foaming behavior of polymer melts.

Effect of talc and diatomite on compatible, morphological, and mechanical behavior of PLA/PBAT blends

Biodegradable nanocomposites were prepared by melt blending biodegradable poly(lactic acid) (PLA) and poly(butylene adipate-co-butylene terephthalate) (PBAT) (70/30, w/w) with diatomite or talc (1–7%). From the SEM test, the particles were transported to the interface of two phases, which acted as an interface modifier to strengthen the interfacial adhesion between PLA and PBAT. Talc and diatomite acted as nucleating agents to improve the crystallization of PBAT in the blends by DSC analysis. Moreover, adding the particles improved the tensile and impact toughness of the blends. The elongation at break with 5% talc was 78% (vs ∼21%) and the impact strength was 15 kJ/m2 (vs ∼6.5 kJ/m2). The rheological measurement revealed that the talc and diatomite reduced the viscosity of the blends. The results showed a good possibility of using talc- and diatomite-filled PLA/PBAT blends with high toughness for green-packaging and bio-membranes application.

A practical application of sensory and rheological measurement in the development of fish pâté quality attributes

The flavor and texture of fish pâté are the most important attributes for consumers. The aim of the study was to analyze and compare commercial fish pâté with a laboratory prototype by combining sensory and rheological measurements. Quantitative Descriptive Analysis and Texture profile were established by expert sensory panelists, while the texture was additionally examined through rheological measurement. The results show a statistically significant difference between samples in relation to four flavor characteristics (color, fish odor, flavor saltiness, p < 0.05) and five texture characteristics (surface, plasticity, spreadability, density, graininess, p < 0.05). Regarding texture profile, the commercial fish pâté showed firmer density, and spreadability than does the laboratory prototype. Sensory and rheological data for both samples were highly positively correlated. Although the laboratory prototype has reached a certain level of desirable characteristics of fish pate (color, taste, spices) the acceptability of the observed differences in texture should be examined on a representative sample of consumers.