INFLUENCE OF MASTICATION ON THE MICROSTRUCTURE AND PHYSICAL PROPERTIES OF RUBBER
The effects of the masticated state of isoprene rubber (IR) at the carbon black (CB) addition stage on subsequent mixing, microstructure, and physical properties in the case of a kneader with a characteristic large-diameter shaft are investigated by examining the mastication-time dependence. A sufficiently masticated IR shows a shorter black incorporation time, which results in an improved dispersion of CB and better physical properties. Observing the microstructure of a rubber compound using the atomic force microscope–based nanomechanical technique, poor CB dispersion is revealed for insufficient mastication. Specifically, large CB agglomerations surrounded by the interfacial rubber region with higher elastic modulus than that of a rubber matrix are formed. Such a large CB agglomeration, on the other hand, does not appear in rubber compounds with longer mastication times. The thickness of the interfacial region becomes shorter in these cases. These observations are further discussed by the concept of “rheological unit” introduced by Mooney et al. This study demonstrates that the microstructure of a rubber compound is highly heterogenous with rubber regions of different microscopic elastic moduli and that the microstructure has an influence on CB dispersion and the physical properties of rubber.ABSTRACT
Kneader with a tangential rotor.
Molecular weight distributions of masticated IR.
Temperature dependence of the viscoelastic properties for masticated IR at different mastication times. (a) G′, (b) G", and (c) loss tangent.
Relationship between the temperature of masticated IR and mastication time.
Mixing chart of the kneader as a function of mastication time. Mastication time: (a) 0.5 min, (b) 1 min, (c) 3 min, (d) 5 min, (e) 10 min.
Relationship between (a) BIT, (b) the total mixing time of the IR compound, and mastication time.
Relationship between the G′ (0.1%)/G′ (4%) ratio at 80 °C of IR and mastication time.
Relationship between the tensile properties and mastication time. (a) Tensile strength (TB), (b) elongation at break (EB), and (c) modulus (M100).
Relationship between (a) the crack length on the De Mattia fatigue measurement, (b) the wear index in DIN abrasion measurement, and mastication time.
(a) JKR elastic moduli mappings, (b) adhesive force mappings by AFM, and (c) TEM images. The scan size of AFM is 3.0 μm and that of TEM is 2.0 μm.
(a) Topographic image (3.0 μm) of mastication time of 3 min and (b) its histogram.
Four-valued mapping images of the JKR elastic moduli. Mastication time: (a) 0.5 min, (b) 1 min, (c) 3 min, (d) 5 min, and (e) 10 min. The supposed rheological units discussed in the “Effect of the State of Masticated IR on Rubber Mixing, Microstructure, and Physical Properties” are depicted as ellipses drawn with dashed line.
Histograms of (a) the adhesive force mapping image and (b) the JKR elastic moduli mapping image without a CB area for 5 min of mastication.
Relationship between mastication time and (a) the fractions of JKR elastic moduli in three rubber regions and (b) the peak values of JKR elastic moduli in two rubber regions.
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