P014_RPN_20150112.qxp 1/7/2015 3:27 PM Page 1 14 Rubber & Plastics News ● January 12, 2015 www.rubbernews.com Technical Examining functionalized butyl rubber By Kevin Kulbaba, An expected increase in the plateau Dana Adkinson and Jon Bielby Executive summary modulus, GN, is observed for the butyl Lanxess Inc. ionomer as ionic aggregates act as phys- Many industrial rubber applications are X_Butyl I4545P is a new butyl-based material that has been developed by ical crosslinks. subjected to cyclical stress or deforma- Lanxess and contains a persistent ionic charge attached to the butyl backbone. In Here, GN is estimated from the G’ at tions, which can cause cracks to initiate addition to the properties of traditional butyl rubber (impermeability and low the frequency of the G” minima. The GN and propagate, leading to failure of the temperature flexibility), this new butyl ionomer displays many unique physical of 3.0x105 Pa obtained for BIIR-h is sim- rubber article. The fatigue process in- and dynamic properties, including excellent green strength, improved polymer- ilar to that of reported values for poly- volves the formation of cracks due to natu- filler interaction and the formation of stable pellets. isobutylene between 2.9x105 Pa to rally occurring flaws or the aging process. Incorporation of the butyl ionomer in an bromobutyl inner liner compound for- 3.2x105 Pa,15-17 while the butyl ionomer As minimizing the propagation of mulation has been shown to provide improved green strength leading to greater was found to be 3.8 x10.5 cracks is critical for many applications dimensional stability needed during extrusion and calendering processes. This increase in modulus is useful in in their service life, improving fatigue is The final cured article shows significant improved crack growth resistance and butyl applications where an increase in a major challenge for dynamically adhesion to carcass compounds without impacting the other compound properties. elasticity is desired or where greater co- loaded rubber products. Such properties may lead to longer lasting tire inner liners, which can be of bene- hesive strength is required, such as for Many types of polymers, fillers, and vul- fit for off-the-road tire manufacturing and retreading operations. adhesives. canization systems are used in rubber ap- Another difference in the butyl plications (all of which are known to influ- ionomer rheology is seen in the decrease ence fatigue behavior)1-2 in order to achieve melt viscosity and relaxation time. The interactions allow for improved green in the mid-frequency (10-2 to 101 rad/s) a wide range of mechanical properties. solubility behavior and the glass transi- strength and polymer-filler interactions as G”, which is normally identified with the Ionomers are polymers that contain a tion temperature also can be affected by well as the formation of stable pellets.10-14 relaxation of the non-functionalized small amount of covalently bound ionic ionic associations.3-8 In Fig. 1, the butyl ionomer is charac- polymer chain through reptation, con- functionality dispersed in a nonpolar ma- Relaxation of the ionic groups is terized through its rheological properties tour length fluctuations and constraint trix. They are an important class of poly- thought to proceed through a mechanism and is evaluated in a halobutyl-based release mechanisms as described by the mers as ionic interactions produce large of “ion hopping” where ion pairs hop to an- rubber compound to demonstrate the per- tube model.18-20 changes in physical, mechanical and rhe- other aggregate, allowing the stress of the formance attributes of this new material. Conversely, for the butyl ionomer, re- ological properties compared with poly- polymer chain segment containing the ion laxation after the entanglement time, Te, mers that do not contain ionic groups.3-8 group to relax.7-9 Raw polymer characterization (Rouse time of the chain segment be- Ionomers are microphase-separated Butyl ionomer is a new class of butyl Fig. 2 displays the storage (G’) and tween entanglements) proceeded through materials, where the ionic groups aggre- polymer that has been developed by the loss (G”) modulus mastercurves of high the “hopping” of ionic aggregates to re- gate into domains, which act as re- generation of permanent ionic groups Mw brominated butyl rubber (BIIR-h) duce the stress as well as relaxation versible crosslinks, strongly influencing bound to the polymer backbone. and butyl ionomer at a reference tem- through reptation.7,21,22 the polymer behavior. In addition to the properties of tradition- perature of 20°C. A maximum in G” was detected for the The ionic clusters affect the viscoelastic al butyl rubber polymers (impermeability Time-temperature-superposition was butyl ionomer at approximately 10 rad/s response with an increase in modulus, and low temperature flexibility), the ionic successful for the ionomer due to the and is attributed to the relaxation of ion- large difference between the entangle- ic aggregates, with T representing the ment and ionic relaxation times. A small average duration of an ion pair multi- Fig. 2. G’ (solid symbols) and G” (open symbols) mastercurves at a reference tem- amount of ionic functionality (0.4 mol plet. The “ion hopping” relaxation mech- perature of 20°C. percent) gave rise to large changes in anism subsequently hindered reptation the polymer’s viscoelastic properties. and imparted a much greater terminal Fig. 1. BIIR-based phosphonium ionomers. The authors Kevin Kulbaba is the technical marketing manager for NAF- TA-focused butyl rubber at Lanxess Inc., located in London, Ontario. His work focuses on business development for butyl rubber materials and applications. Kulbaba has more than 17 years of experience in the field of polymer science, including 12 years with elastomers and rub- ber compounding. He studied chemistry at the University of Western Ontario and obtained his doctorate in inorganic polymer chemistry at the University of Toronto. Fig. 3. Temperature dependence of the shift factors. Kulbaba is a member of the Canadian Society of Chemistry, American Chemical Society and the On- Kulbaba tario Rubber Group. Dana Adkinson is a senior research scientist at the Research and Development Center for Lanxess in London. She focuses on the development of new butyl-based materials geared to- ward expanding the application scope of butyl rubber. She received her doctorate in chemistry from the Universi- ty of Western Ontario in 2005. Her work has resulted in more than 12 patent ap- plications. Jon Bielby is a senior research scientist at the Global Research and Development Cen- Adkinson ter for the Butyl Rubber Business unit of Lanxess in London. He leads the physical and dynamic material research laborato- ry in support of the development of new butyl-based materials, fo- cusing on expanding the application scope of butyl rubber. He received his degree in physics from the University of Waterloo in 1996 and accepted a position at Lanxess (then Bayer) in 2000. Bielby P015_RPN_20150112.qxp 1/7/2015 3:29 PM Page 1 www.rubbernews.com Rubber & Plastics News ● January 12, 2015 15 Technical relaxation time or disentanglement fore, creep testing was employed to de- cal properties for the blend compounds. inner liner with repeated heat cycles. time, Td, on the polymer to such an ex- termine the terminal response, with the Table II outlines the change in Mooney Crack propagation was determined tent that it is not measurable in the ex- zero shear viscosity being calculated: viscosity and Mooney scorch of the using a DeMattia flex tester on samples perimental window. halobutyl blend compounds relative to the that were aged for one week at 100°C. This indicates that the butyl ionomer control. The 10 percent increase in Mooney The results show that the rate of crack may be more difficult to handle than viscosity can be attributed to improved propagation for the BB-ION10 blend BIIR-h in certain industrial processes. filler dispersion and the presence of low was comparable to the control formula- The temperature dependence of the concentrations of ionic aggregates at such tion while the crack propagation for the experimental shift factors, aT, used to where JN(t) is the Newtonian creep com- temperatures. BB-ION20 compound was enhanced (re- construct the viscoelastic mastercurves pliance.27 Table II also highlights the change in fer to Fig. 6). obeyed the Williams, Landel and Ferry Fig. 5 displays the shear creep curves green strength relative to the mill shrink- Since the physical crosslinks due to equation:15,23 of BIIR-h and butyl ionomer. The creep age of the compounds. the ionic interactions are reversible, the response validated the impact of only a Significantly, the blends shows a 40-90 incorporation of the butyl ionomer into small amount of ionic content towards percent improvement in green strength the polymer matrix appears to impart the rheological properties as the creep of (peak stress) with no negative impact on self-healing properties, whereby the ion- the butyl ionomer is greatly reduced. the mill shrinkage, thereby resulting in ic aggregates break and re-form. The zero shear viscosity was found to an enhancement in dimensional stability Thus, a substantial reduction in the While polyisobutylene is known for its increase by more than a decade from of an uncured compound without signifi- fatigue properties of the cured rubber weak temperature dependency,24-26 the 3.6x108 Pa-s for BIIR to 4.2x109 Pa-s for cantly increased nerve, which is desir- article could be realized once again with shift factors were influenced strongly by butyl ionomer. Lower Mw brominated able for extrusion or calendering opera- the addition of low levels of the butyl 8 ionic functionality as the temperature butyl rubber (BIIR-l), with a ␩0 of 1.82x10 tions.