Rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend

ABSTRACTPoly(lactic acid) (PLA) was melt blended with low density polyethylene (LDPE) with the aim of replacing commodity polymers in future applications. Because cost of PLA is quite high, it is not economically feasible to use it alone for day to day use as a packaging material without blending. In this work, PLA was blended with LDPE in different ratios by using a laboratory scale single screw extruder. The prepared blends were characterized in terms of rheological and mechanical properties. Rheological properties were studied using a capillary rheometer, and the Bagley's correction was performed. True shear rate (γr), true shear stress (τr), true viscosity (ηr) and non‐Newtonian index (n) were determined. The relationship between true viscosity and temperature was also studied, and the flow activation energy at a constant shear stress (Eτ) was determined. The mechanical properties of the blends were investigated on dog bone‐shaped samples obtained by injection molding, tensile tests were performed using Testometric M350‐10KN, stress at break, strain at break and Young's modulus were determined. Rheological results show incompatibility between the two polymers where the true viscosity of the blend decreased with increasing PLA content below the line of mixing rule, also it was found that the blend exhibits shear‐thinning behavior over the range of the studied shear rates. The mechanical results also showed incompatibility between PLA and LDPE in the blend, where stress at break and Young's modulus of the blend increased with increasing PLA content, whereas strain at break of the blends was similar to that of neat PLA. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd.

Binary and ternary blends of poly(lactic acid) (PLA), polystyrene (PS) and acrylonitrile-butadiene-styrene (ABS) were prepared using a one-step extrusion process. Rheological and mechanical properties of the prepared blends were determined. Rheological properties were studied using a capillary rheometer, shear rate, shear stress, non-Newtonian index, shear viscosity and flow activation energy were determined. Mechanical properties were studied in term of tensile properties, stress at break, strain at break, and Young’s modulus were determined. The effect of the composition on the rheological and mechanical properties was investigated. The results show that the ternary blend exhibits shear-thinning behavior over the range of the studied shear rates where the true shear viscosity of the blend decreases with increasing true shear rate, also it was found that the true viscosity of the blend decreases with increasing ABS content. The mechanical results showed that, in the most cases, the stress at break and the Young’s modulus improved by the addition of ABS.

A continued increase in the use of plastics has led to an increasing amount of plastics ending up in the waste stream; and the increasing cost of landfill disposal and public interest in support of recycling has meant that plastics recycling must increase. In this work, the effect of multiple extrusion and injection of poly(lactic acid)/polystyrene polymer blend (PLA/PS) on its rheological and mechanical properties is presented. Rheological properties were studied using a capillary rheometer, apparent shear rate (γ a), apparent shear stress (τ a), apparent viscosity (η a), and flow activation energy were determined. The mechanical properties of the blend were investigated on dog bone-shaped samples obtained by injection molding, tensile tests were performed, stress at break, strain at break, and Young’s modulus were determined. The results showed that the apparent viscosity of PLA/PS blend decreases monotonously with increasing the processing number. Also it was found that stress and strain at break of the blend decrease sharply after two processing cycles, whereas the processing number has a little effect on Young’s modulus.

A modification of the piston head of the Instron rheometer has enabled its use in studying rheological properties of SBR elastomers over a shear rate range of 30–2500 sec.−1. In place of the usual piston head, a Teflon plug with a cavitated bottom was used. This eliminates leakage between the piston and barrel and results in uniform force traces that can be extrapolated to zero barrel length to yield the total force of extrusion. Hence, it gives a practical means to study, on sound theoretical basis, the rheological properties which are all important in the prediction of factory processing behavior and factors which influence it. Extrusions of SBR 1712 and 1712-HAF compound were made through capillaries having 180° entrance angles, diameters of 0.033, 0.043, 0.052, and 0.070 in. and length/diameter ratios near 1, 2, 4, 6, 8, and 10 at temperatures of 80, 90, 110, and 130°C. and crosshead speeds of 1/2, 1, 2, and 5 in./min. Linear fits were found between length/diameter (L/D) ratio and the force of extrusion (at zero barrel length). The slopes of these lines give values of true shear stress which fit one relationship to Newtonian shear rates at each of the four temperatures independent of die dimensions. Plots of log true shear stress versus log true shear rate show curvilinear behavior for clear SBR 1712 elastomer over the entire shear rate range of 45–3900 sec.−1 at all four temperatures. The same plots for the HAF compound of SBR 1712 showed curvilinear behavior below shear rates of 100 sec.−1 and linear behavior above with a power law exponent of 6.1. There is a great difference in slopes between lower and higher shear rates at all four temperatures. This indicates that extrapolation from low shear rate instruments cannot be made to predict behavior at higher rates common to factory equipment. This observation holds for both clear SBR 1712 elastomer and its HAF compound. True shear stresses at corresponding true shear rates (and therefore viscosities) were considerably higher for the compound than for the clear elastomer, as was expected. However, the addition of black reduces the extent of deviation from Newtonian behavior. Even though uncorrected for recoverable shear strain, viscosities were calculated and used to calculate activation energies according to the Arrhenius equation. Straight lines were obtained covering temperatures at 90, 110, and 130°C. at all shear rates with activation energies of 1.5 kcal./mole of both the clear elastomer and its compound. Log viscosity at 80°C. in all cases was above the straight lines through the log viscosities at the other three temperatures. This indicates a higher activation energy at temperatures below 90°C. Addition of black apparently does not affect substantially the identity of the rheological unit. Extrusion die swell was found to decrease with increasing temperature and increasing L/D ratio at all rates of shear. At a given temperature it increases rate of shear. Swell was anisotropic for the clear elastomer but not for the compound.

The effects of wood fibers on the rheological and mechanical properties of polystyrene/wood (PS/wood) composites were investigated. The composites with different ratios of PS and wood were prepared by means of internal mixer and, additionally, two different sizes of the wood particles were used, such as ∼100 and ∼600 µm. The rheological properties were studied using capillary rheometer, apparent shear rate, apparent shear stress, apparent viscosity, power law index, and flow activation energy at a constant shear stress were determined. The rheological results showed that the shear stress–shear rate variations obeyed a power law equation, and the composites exhibited shear thinning. The flow activation energy of the composites increased with the addition of wood particles. Mechanical results showed that stress at break of the composites was higher than that of pure PS, whereas the strain at break and impact strength of the composites were lower than that of PS. In addition, the mechanical properties of the present composites were improved when the small size of wood particles were incorporated.

ABSTRACTThe influence of acrylonitrile–butadiene–styrene (ABS) copolymer content on the properties of polylactic acid (PLA)/low density polyethylene (LDPE) blend (50/50) was investigated in the present paper. The blend (PLA/LDPE/ABS) was prepared in different ratios using a laboratory scale single screw extruder. The prepared blends were characterized in terms of rheological and mechanical properties. Rheological properties were studied using a capillary rheometer, and the Bagley's correction was performed. Shear rate (γr), shear stress (τr), shear viscosity (ηr), and non‐Newtonian index (n) were determined. The relationship between shear viscosity and temperature was also studied, and the flow activation energy at a constant shear rate (Eγ) was determined. The mechanical properties of the blends were investigated on dog‐bone‐shaped samples obtained by an injection molding machine. The tensile tests were performed using Testometric M350‐10KN, and the stress at break, strain at break, and Young's modulus were determined. Rheological properties revealed that the blend exhibited shear‐thinning behavior over the range of the studied shear rates, and the viscosity of the blend increased as the ABS content increased, whereas the flow activation energy decreased. Based on the mechanical properties determined for the prepared blends, it was found that no relation between ABS content and stress at break of the blend was regarded, whereas Young's modulus was significantly improved by the addition of ABS. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

In this work, rheological and mechanical properties of acrylonitrile–butadiene–styrene/corn starch composites (ABS/starch) were studied. The composites were prepared using a laboratory-scale, single-screw extruder. Rheological properties were determined using the single-screw extruder, apparent shear rate (γ a ), apparent shear stress (τ a ), apparent viscosity (η a ), non-Newtonian index (n), and flow activation energy at a constant shear rate (E γ) and constant shear stress (E τ). Mechanical properties in terms of tensile tests were performed using Testometric M350-10KN, stress at break, strain at break, and Young's modulus were determined. Rheological results showed that the composites are pseudo plastic in behavior, and the apparent viscosity of the composites increases with increasing starch content above the additive rule, which indicates a partial compatibility in the composite. It was also found that the flow activation energy of the composite increases with increasing starch content. The mechanical results showed that the strain at break of the composite decreases sharply by the presence of starch, whereas the Young's modulus increases with increasing starch content.

In this work, rheological properties of poly (lactic acid) (PLA), low density polyethylene (LDPE) polymer blends were investigated in the molten state. The experiments were carried on a capillary rheometer. The effect of shear stress, temperature and blending ratio on the flow activation energy at a constant shear stress and melt viscosity of the blends are described. The results showed that the PLA/LDPE polymer blends are pseudo plastic in nature, where there viscosity decreases with increasing shear stress. Also it was found the melt viscosity of the blends decreases with increasing PLA content in the blend.

The viscosities of a number of monodisperse polystyrene melts have been measured using a capillary rheometer. The materials covered a molecular weight range of 43,000–460,000. Shear rates of 1.54–1540 sec.−1 and temperatures of 350–450°F. were studied. The effect of molecular weight distribution of polydisperse polystyrene was also measured. It was found that while low shear viscosity was dependent on Mw, higher shear melt viscosities depended on averages between Mw and Mn until at 1000–2000 sec.−1, Mn controlled viscosity. Agreement with the 3.4‐power dependence of zero shear viscosity was good. Similar exponential relationships were found, with higher rates of shear, corresponding to smaller values of the exponent. Constant values of the exponent were found at constant shear stress but not at constant shear rate. Agreement with the constancy of the activation energy for viscous flow for various molecular weights and distributions at constant shear stress was good. However at constant shear rate, ΔE decreased as the molecular weight average increased and as the distribution broadened. Viscosity versus shear rate master curves were constructed by using the Buehe‐Harding procedure. All monodisperse polystyrenes showed excellent fit with the master curve. Other molecular weight distributions did not. Master curves also were constructed for measurements of dynamic viscosity versus frequency for monodisperse polystyrene. These curves when compared to steady state viscosities failed to confirm the correspondence of ηa to either |η*| or to η′.

ABSTRACTPoly(lactic acid) (PLA), a biosource, biodegradable polymer, is not suitable for some important polymer processing operations, such as film blowing and blow molding, due to its low melt strength. Moreover, while it has high tensile modulus and strength in the solid state, it exhibits low ductility. The present work is an extension of our earlier effort to improve the processability and mechanical properties of PLA by blending with poly[(butylene succinate)‐co‐adipate)] (PBSA), a biodegradable polymer with lower glass transition temperature. We evaluate the influences of incorporation of an epoxy chain extender and nanoclay on the properties of the blend. Since earlier work was conducted in a batch mixer, the influence of melt processing in the twin screw extruder and the differences between products obtained in the extruder and the batch mixer are evaluated and explained. Based on earlier work, the following PLA/PBSA blend ratios of 90:10, 80:20 and 70:30 were selected. All the samples were prepared in the twin‐screw extruder at two different screw speeds (50 and 150 rpm), to evaluate the effects of residence time and shear rates. The morphology and structure of the blends were examined using field emission scanning electron microscopy. Transmission electron microscopy (TEM) and X‐ray diffraction (XRD) were used to evaluate the levels of intercalation and exfoliation in the nanocomposites. The chain extension reaction was evaluated using nuclear magnetic resonance (NMR) spectroscopy and other techniques. Rheological properties (dynamic oscillatory shear and elongational viscosity measurements) and mechanical characteristics of the pure components, blends, and nanocomposites were studied and discussed in light of the composition and morphology of the blends and the nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42664.

Melt rheology and extrudate swell properties of talc filled polyethylene compounds

Crystallization, melting, hydrolytic degradation, and mechanical properties of poly(trimentylene terephthalate)/poly(lactic acid) (PTT/PLA) blends have been investigated. The blends show a single and composition-dependent glass-transition temperature (T g) over the entire composition range, implying that these blends are fully miscible in the amorphous state. The observed T g is found to increase with increasing PLA content and fitted well with the Gordon–Taylor equation, with the fitting parameter k being 0.91. The cold-crystallization peak temperature increases, while the melt-crystallization peak decreases with increasing the PLA content. Both the pure PTT and PTT/PLA blends cannot accomplish the crystallization during the cooling procedure and the recrystallization occurs again on the second heating. Therefore, on the thermogram recorded, there is exothermal peak followed by endothermal peak with a shoulder. However, to pure PLA, no crystallization takes place during cooling from the melt, therefore, no melting endothermic peak is found on the second heating curve. WAXD analysis indicates PLA and PTT components do not co-crystallize and the crystalline phase of the blends is that of their enriched pure component. With increasing PLA content, the hydrolytic degradation of the blend films increases, while both the tensile strength and the elongation at break of the blend films decrease. That is to say, the hydrolytic degradation of the PTT/PLA blends increases with the introduction of PLA at the cost of the decrease of the flexibility of PTT.

Binary and ternary blends of poly lactic acid (PLA), acrylonitrile-butadiene-styrene (ABS) and tapioca cassava starch (TCS) were prepared by the help of melt blend method. Rheological and mechanical properties of the prepared blends were studied. Rheological properties were studied using capillary Rheometer, shear rate, shear stress, the non-Newtonian index, were determined .Mechanical properties were studied in terms of tensile properties, stress at break, strain at break and Young's modulus have been determined by help of Universal Test Machine (UTM-3969).The results shows the ternary blends reveals shear-thinning behavior, over the range of the studied shear rates where the true shear rate of the blend decreases while increasing the shear rate. It also found that the true viscosity of the blend decreases with increased ABS content.

Vinyl ester resins with varied acid values (11, 22, 32, 38, and 48 mg KOH/g solid) were prepared by reacting epoxy-novolac resin with methacrylic acid. The rheological behavior of these synthesized vinyl ester resin (VER) samples containing styrene as reactive diluent was studied using a Haake Rotovisco RV 20 viscometer. The apparent viscosity was found to be inversely proportional to the square root of the acid value in the temperature range of 25–40°C and at shear rates ranging from 100–800 sec−1. The zero-shear viscosity of these VER samples containing styrene (40% w/w) as reactive diluent decreased linearly with temperature. The activation energies for flow at constant shear stress (25–100 Pa) for a particular sample were found to be constant. The activation energy at constant shear rate decreases with the increase in the shear rate (50–400 sec−1). The activation energy at constant shear rate and shear stress decreased with the increase in the acid value. The viscosity of vinyl ester resin containing styrene as reactive diluent decreased almost 50 times with the increase in the concentration of reactive diluent from 30% to 100% (w/w of the resin).

Melt rheology of poly(vinylidene fluoride) (PVDF)/low density polyethylene (LDPE) blends