Asphaltenes as a tackifier for hot‐melt adhesives based on the styrene‐isoprene‐styrene block copolymer

Abstract

The use of heavy crude oil asphaltenes and resins (termed asphaltenes) as the components of hot‐melt adhesives based on the styrene‐isoprene triblock copolymer was considered. The rheological, thermophysical, strength, and adhesive characteristics of the mixtures containing from 10 to 40 wt% of asphaltenes were studied. The addition of 10 to 20 wt% of asphaltenes enhanced the strength and adhesive properties of the mixtures and only slightly changed their rheology. The higher concentrations of asphaltenes reduced the viscosity of the mixtures but did not lead to improved characteristics of the adhesives. The ambiguous effect of asphaltenes is probably due to their uneven distribution between the microphases of the block copolymer as well as their ability to act both plasticizers and reinforcing particles depending on temperature. A comparison of asphaltenes and conventional tackifiers based on hydrocarbon resins revealed their comparable effect on the properties of the block copolymer.

Hot-Melt and Pressure-Sensitive Adhesives Based on Styrene-Isoprene-Styrene Triblock Copolymer, Asphaltene/Resin Blend and Naphthenic Oil

“…In the region of low frequencies ( ω < 1 rad/s), the loss modulus exceeds the storage one, i.e., SIS behaves more like a liquid and is able to function as a hot melt adhesive at sufficiently long observation times. In the high frequency region, SIS pass into the glassy state (due to the proximity of the test temperature to the glass transition temperature of polystyrene blocks, which is 75 °C [ 81 ]) and loses its ability to spread and stick under short-term exposure (less than 1 s).…”

“…Meanwhile, the introduction of ARB does not reduce the SIS cohesive strength but rather slightly increases it ( τ c , Table 1 , a note to the table contains statistical analysis data). This can be related to the fact that resins and asphaltenes pass into a glassy state upon cooling down to 25 °C and no longer plasticize the block copolymer; moreover, asphaltenes start to play the role of reinforcing particles [ 81 , 82 ]. In contrast, the addition of the same amount of oil (40%) to SIS expectably reduces its tensile strength by three times.…”

“…Moreover, the more the ARB content, the higher the shear and pull-off strength of the adhesive joints of the hot melt adhesive (and the data are becoming more statistically significant, see the note to Table 2 ). This may be due to both an increase in the cohesive strength of the mixture and an improvement in the wetting of the substrate by the adhesive when ARB is added to it [ 81 ]. However, the nature of the joint destruction is adhesive and the increase in the cohesive strength of the adhesive cannot be the main reason for improving its adhesive properties.…”

“…However, natural compounds that are close in physical–chemical properties to hydrocarbon resins are present in heavy crude oil and bitumen. Such compounds are called asphaltenes [ 80 ], whose rheology is similar to that of conventional tackifiers and which, like them, can form miscible (at least partially) blends with certain polymers [ 81 , 82 ].…”

“…Resins are natural crude oil surfactants [ 96 , 97 , 98 , 99 ] that stabilize asphaltenes [ 100 ] and improve their interaction with various media, including polymer matrices [ 81 ]. However, the viscosity of resins and asphaltenes is quite high even in the molten state [ 95 ], so a plasticizer may still be required to create a polymer adhesive.…”