Rheological Properties of Polyethylene Color Masterbatches Containing Pigment RED 122 (2,9-Dimethylquinacridone) Modified by Silanes Using Pulverization Method

Abstract

Polyethylene color masterbatches containing pigment RED 122, 2,9-dimethylquinacridone, ((2,9-dimethyl-5,12-dihydroquinolino[2,3-b]acridine-7,14-dione) modified by the pulverization method in ball mills were obtained. As pigment-modifying agents, isobutyltrimethoxysilane IBTMS and octyltrietoxysilane OTES were used. The viscoelastic properties of the prepared masterbatches were investigated by using an oscillation rotational rheometer. The impact of the 2 wt.% of coloring masterbatch on the rheological behavior of polyethylene during processing at 170 °C was analyzed. Storage shear modulus G', loss shear modulus G″, complex viscosity η* and loss factor tan δ were analyzed. Modification prevents the agglomeration of modified pigment particles in the masterbatch, leading to a significant increase in the storage shear modulus G', from 13.83 kPa (masterbatch containing pigment RED 122) to 58.74 kPa (pigment modified with 2 wt.% of IBTMS) and 49.67 kPa (pigment modified with 2 wt.% of OTES). The analysis of the continuous relaxation models showed that the modified pigment influenced the relaxation of melted polyethylene. The tendency of the silane-modified pigment to create its "own structure" in the polyethylene carrier via particle-particle interactions was estimated based on rotational tests at low and high shear rates. The larger area of viscosity loops was determined at 170 °C for the masterbatch containing 1 wt.% of OTES-modified pigment, 2574.44 Pas(1/s), as compared with the reference masterbatch, 464.88 Pas(1/s). The Carreau and Carreau-Yasuda viscosity models were applied to analyze the flow curve and the changes in viscosity as a function of the shear rate. After pigment modification, the zero shear viscosity µ₀ of the mixtures of polyethylene/pigment masterbatch changed from 234.9 Pas (pigment RED 122) to 305.9 Pas (pigment modified with 1 wt.% of IBTMS). The influence of the modified pigments on the crystallization of polyethylene and its thermal stability was investigated. The temperatures of melting T_m were determined.

Keywords: polyethylene masterbatches; quinacridone pigments; viscoelastic properties.

Figure 1

The chemical structure of 2-9-dimethylquinacridone pigment.

Figure 2

The chemical structure of modifying agents: (a) isobutyltrimethoxysilane IBTMS, (b) octyltriethoxysilane OTES.

Figure 3

A diagram illustrating the method of pigment RED 122 modification by silanes used and the masterbatch production process.

Figure 4

The SEM pictures of pigment RED 122 at magnifications of 1000, 5000, 50,000 and 100,000 times (SEM microscope, LEO 1530 Gemini, producent Zeiss/Leo, Oberkochen, Germany). Red circles mark the stacked together large pigment aggregates.

Figure 5

The SEM pictures of pigment RED 122 modified with 1 wt% of isobutyltrimetoxysilane IBTMS at magnifications of 1000, 5000, 50,000 and 100,000 times (SEM microscope, LEO 1530 Gemini, producent Zeiss/Leo, Oberkochen, Germany).

Figure 6

dTGA plots of silane-modified RED 122 pigment: (a) pigment modified with 1 and 2 wt.% of IBTMS; (b) pigment modified with 1 and 2 wt.% of OTES.

Figure 7

The reflectance plots for RED-1% IBTMS (a) and RED-1% OTES pigment (b). Blue curve – the reference Pigment RED 122, Green plot modified pigment, respectively RED-1% IBTMS (a), RED-1% OTES (b).

Figure 8

The storage shear modulus G′ (a) and loss shear modulus (b) measured at 170 °C as a function of oscillation strain for the masterbatches containing pigment RED 122 and IBTMS and OTES silane-modified pigments; the angular frequency applied was 10 rad·s⁻¹.

Figure 9

Complex viscosity η* measured at 170 °C as a function of oscillation strain for the masterbatches containing pigment RED 122 and silane-modified pigments; the angular frequency applied was 10 rad·s⁻¹.

Figure 10

Loss factor tan δ measured at 170 °C as a function of oscillation strain for the masterbatches containing pigment RED 122 and silane-modified pigments; the angular frequency applied was 10 rad·s⁻¹.

Figure 11

Storage shear modulus G′ (a) and loss shear modulus G″ (b) measured at 170 °C as a function of angular frequency for the masterbatches containing pigment RED 122 and silane-modified pigments; the oscillation strain applied was 0.5%, and the temperature was 170 °C.

Figure 12

Continuous relaxation spectra for polyethylene samples containing 2 wt.% of various masterbatches melted at 170 °C (a). Normalized relaxation spectra H_i/H_max = f(τ_i) for melted samples containing 2 wt.% of masterbatches (b).

Figure 13

Complex viscosity η* measured as a function of temperature for the masterbatches containing pigment RED 122 and silane-modified pigments (a), and for the polyethylene containing 2 wt.% of added masterbatches (b); the applied angular frequency was 10 rad·s⁻¹, the applied oscillation strain was 0.02%, and the heating rate was 5 °C·min⁻¹.

Figure 14

Shear viscosity μ of masterbatches containing RED 122 pigment and pigments modified by silanes. The rotational tests were carried out at 170 °C as a function of the applied shear rate in range of 0.001–300 s⁻¹. A—the Newtonian plateau for the pure polyethylene; B—the zone of shear thinning behavior of the pure polyethylene.

Figure 15

Shear viscosity μ of masterbatches containing RED 122 pigment and pigments modified by IBTMS and OTES silanes measured at 170 °C as a function of the shear rate. Index A in the graph means that the viscosity was measured using an increasing shear rate; index B means that the viscosity was measured using a decreasing shear rate.

Figure 16

dTGA plots of polyethylene containing 2 wt.% of pigment RED 122 color concentrate (MB) and IBTMS silane-modified RED 122 pigment or 2 wt.% of color concentrate containing pigment modified with OTES.

Figure 17

SEM pictures of pellets of masterbatch MB containing RED 122 pigment (concentration pf pigment 30 wt.%) at magnifications of 25,000 times. The pictures were taken as a cross-section of the granulate along the X axis (a) and as a cross-section along the Y axis of the granulate (b). Red circles mark the pigment aggregates and voids in material structure.

Figure 18

SEM pictures of pellets of masterbatch MB_IBTMS 1% (a) and MB_IBTMS 2% (b). The pictures were taken as a cross-section of the granulate along its X axis. Red circle marks the pigment aggregates.

Figure 19

SEM pictures of pellets of masterbatch MB_OTES 1% (a) and MB_OTES 2% (b). The pictures were taken as a cross-section of the granulate along its X axis. Red circle marks the pigment aggregates.