Investigations of Highly Dispersible Silica Types and Silane Types in an OTR Cut Resistant Tire Tread Application

Rolling resistance has an analog in the Off-The Road (OTR) tire market referred to as Ton Mile Per Hour (TMPH).  This is an index of the heat generation as measured by tread temperature with respect to the load carried by the tire.  Improving the TPMH can increase the durability of the tire through reducing the tire operating temperature.  The application of the silica/silane technology tire has been tried earlier, but has had some limitations in “tearing, cut and chip” resistance.  The largest cause for tire removal in mining operations is related to rock damage.  It is estimated that this failure mode may be the cause for as high as 60 to 70 % of tire removals.  This work looks to optimize the use of silica by studying, in a partial factorial design of experiments (DOE). The effects of silica surface area and silane types to improve the cut resistance while producing a high TMPH of OTR tire tread compounds is investigated.

Hence the objective of this work to find an optimum formulation having low heat generation while providing high elongation and facture strength while at the same time having comparable or higher modulus.  The fracture improvement goal is to increase the elastic limit while increasing the stress storage capacity of the material.  The analysis will summarize the relative strength of each of these factors for these objectives of rubber viscoelastic and physical properties.

This study includes two highly dispersible tire silicas: ULTRASIL® 7000 GR with a specific surface area (SSA), measured by Cetyl trimethylammonium bromide (CTAB) adsorption, of 160 m²/g and ULTRASIL® 9100 GR with a SSA CTAB of200 m²/g.  Both silicas are evaluated at typical OTR loadings at different blend ratios with carbon black.  Silanes are varied as DOE factors to maintain or improve fracture resistance.  The silane DOE factors are: type of silane being sulfur crosslinking Si 69® (TESPT) or silanes providing lipophilic modification. The character of the lipophilic silane (alkyl chain length) provided by Dynasylan® PTEO (propyl) or Dynasylan® OCTEO (octyl) silanes; the total dosage of both silane types; and finally, the ratio of the silica-rubber coupling versus lipophilic hydrophobation of the silica surface.