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Comparison of the performance of vulcanized rubbers and elastomer/TPE/iron composites for less lethal ammunition applications.


Composites are a very important class of materials in polymer science and engineering [1]. Composites have superior properties compared to those of the individual components, providing synergy between the phases. Polymer composites usually contain finely distributed reinforcing materials within a plastic or rubber phase. One of the oldest examples is thermoset carbon-filled rubber [2]. The carbon black is distributed in the elastomer phase at the micron level and forms a reinforcing network [2]. Another example is impact-modified thermoplastics. For instance, high-impact polystyrene (HIPS) contains micron-sized polybutadiene rubber particles, some of which are chemically attached to the polystyrene phase. Interestingly, one of the earliest examples of nanostructured materials are thermoplastic elastomers (TPEs) in which the plastic phases are distributed in a continuous elastomer phase at the nanometer scale [3, 4]. TPEs can be categorized as segmented multiblock and triblock copolymer-based TPEs, thermoplastic olefin blends (TPOs), or dynamically vulcanized TPEs (thermoplastic vulcanizates [TPVs]) [5]. Generally, in a block-type TPE with a soft elastomeric continuous phase and discreet nanometer-sized rigid plastic phases, the hard segments provide physical cross-links and determine the mechanical strength, heat resistance, and upper service temperature of the TPE, and strongly affect the oil and solvent resistance. The chemical nature of the soft segments, on the other hand, has an influence on the elastic behavior, low temperature flexibility, thermal stability, and aging resistance. The ratio of soft and hard segments determines the overall properties of a block-type TPE. The "cross-links" by the hard domains are physical in nature, which makes them reversible; hence, TPEs can be processed as plastics and are recyclable. They combine the advantages of low fabrication cost and recyclability associated with thermoplastics, and low hardness and elasticity associated with thermoset rubbers. Well-known examples of triblock-type TPEs are the styrenic block copolymers with a general formula SES, where S represents the hard amorphous polystyrene blocks and E represents the soft elastomeric block. Poly(styrene-block-butadiene-block-styrene) (SBS) and poly(styrene-block-isoprene-block-styrene) (SIS) were first commercialized in the 1960s and are available in a wide range of hardnesses, depending on the polystyrene to polybutadiene or polyisoprene ratio. Poly(styrene-block-isobutylene-block-styrene) (SIBS) is a newly commercialized block-type TPE, with inherent high damping properties due to the polyisobutylene (PIB) segment [6-8]. Together with chemical and heat resistance, exceptional low temperature properties, ease of processing, and recyclability make this TPE a suitable candidate for a wide variety of applications. Butyl (isobutylene isoprene rubber [IIR]), the well-known specialty elastomer, is also based on PIB, containing a small amount (1-3 mol%) of isoprene for cross-linking sites. IIR is known for low permeability and high damping, and is more resistant to environmental conditions than highly unsaturated rubbers (butadiene or isoprene rubbers; BR and IR), due to the lower number of double bonds present [9]. Based on the attributes of SIBS and IIR, they were selected as polymeric matrix for developing less-lethal ammunition (LLA) with desired performance in terms of impact and low temperature properties. Instead of chemically cross-linking IIR with sulfur, SIBS was used to provide shape retention. In order to achieve the desired density, SIBS/IIR blends were filled with iron, and an IIR/SIBS/iron 50/50/233 was used to build a new LLA (J.E. Puskas, B. Kumar, A. Ebied, and B. Lamperd, U.S. patent applied for in 2003 [10]).

The use of lethal force by law enforcement agencies is becoming politically and socially unacceptable. It has always been desirable by the corrections community to achieve control without causing serious injuries by using various nonlethal or less-lethal weapons [11]. The demand for less-lethal weapons has led manufacturers to develop new devices for law enforcement agencies. Unfortunately, less lethal technologies to date have proven to be either impractical or ineffective, or a combination of both [12]. Reportedly, the single most important legal issue that faces law enforcement, correctional administration, and public managers is the liability issue for misusing less-lethal weapons [13]. The importance of developing improved LLAs for peacekeeping applications (e.g., for a handgun that can target a hijacker in a cockpit without penetrating the air-plane's fuselage, or can be used in crowd control events) was also realized after the September 11, 2001 terrorist attacks in the United States. Unfortunately, it appears that LLA such as plastic and rubber bullets have been developed on a trial-and-error basis, with the error resulting in tragic circumstances [12-18]. There are barely any scientific articles in this field, with most of the material-related information available in patents.

A patent by Bilsbury et al. [19] discloses a practice ammunition projectile composed of a compacted blend of fine lead particles and thermoplastic resins such as poly(ethylene terephthalate) or poly(butylene terephthalate). With 60 wt% lead, these projectiles had a density of 7 [gcm.sup.-3]. The use of environmentally toxic lead is undesirable, since during firing of the projectile lead vapors can be released into the air.

Another patent, filed in 1993 by Belanger et al. [20], discusses the development of practice ammunition consisting of a compacted mixture of fine copper powder, Nylon 11 or nylon 12, and a coupling agent such as organo-zirconate to accommodate the high copper loading of 90 wt% that resulted in an overall density of 5.7 [gcm.sup.-3]. The primary aim of developing this composite was to provide lead-free practice ammunition. Considering the high copper loading, along with the high hardness of copper (Brinell hardness 874 MN[m.sup.-2]), such a projectile would most likely cause severe injuries.

The 1982 patent by Lefebvre [21] discloses a rubber bullet having a Shore A hardness of 40-55, with a diameter less than the bore of the gun barrel. Examples of carbon black-filled thermoset rubbers disclosed in this invention include ethylene-propylene-diene rubber (EPDM), natural rubber (NR), synthetic polyisoprene (IR), and polybutadiene (BR) rubbers, with carbon-black loading of 150 parts per hundred rubber (phr) with 24 phr of processing oil.

In another patent, Dubocage et al. [22] disclose a projectile based on cross-linked BR filled with metallic powder, cross-linking carboxyl-capped polybutadiene with a poly-epoxide. Typical metal fillers cited include iron, iron alloys and compounds, barium compounds (such as barium sulfate), and tungsten and tungsten alloys, yielding a compound density between 2 and 2.9 [gcm.sup.-3]. The composite was then molded into a ball and compressed into a gun shell.

In our earlier report, based on FTIR and energy dispersive X-ray (EDX) measurements, we reported the composition of four existing rubber projectiles: the rocket, the tube, the monoball, and the multiball rounds, shown in Fig. 1 [10].

The rocket projectile was found to consist of an EPDM-carbon black-based composite with Shore A hardness of 62 and density of 1.4 [gcm.sup.-3]. The tube projectiles were made of carbon black-EPDM/styrene-butadiene rubber (SBR) filled with aluminosilicate/calcium carbonate, with Shore A hardness of 62 and density of 4.1 [gcm.sup.-3]. The monoball projectile consisted of an NR/IR/aluminosilicate-based composite with Shore A hardness of 46 and density of 1.6 [gcm.sup.-3]. The multiball rounds were made of an EPDM-calcium carbonate-based composite with Shore A hardness of 62 and density of 1.3 [gcm.sup.-3]. These LLAs were also tested for energy transfer, which was correlated with blunt impact causing treatable injuries based on the work of Bir et al. [23]. They specified a maximum allowable deflection of 6.93 mm and the maximum tolerable energy transfer of 3700 N on impact without serious injury in the thoracic region. With the desirable 76 [ms.sup.-1] (250 [fts.sup.-1]) muzzle velocity, this translated to a weight of about 15 and 25 g, for 20- and 12-gauge projectiles, respectively. This in turn defined the minimum density of the projectiles to be 2.4 [gcm.sup.-3]. The 12- and 20-gauge projectiles were designed and manufactured using the SIBS/IIR/iron 50/50/233 composite; the details have been reported [10].


The concept of TPE/non-cross-linked elastomer blends is applicable to different block-type TPEs and elastomers. This article will compare the performance of various highly-filled TPE/elastomer composites in terms of hardness, creep, and dynamic mechanical properties. It will be shown that the SIBS/IIR/iron 50/50/233 composite has unique dynamic properties, which are best suited for LLA applications.



Butyl elastomer (IIR, grade RB301, unsaturated, 1.6 mol%, Mooney viscosity [M[L.sub.1+8], 125[degrees]C], 51) was obtained by courtesy of Bayer Inc., Sarnia, Ontario, Canada. SIBS (grade 73T, 30 wt% polystyrene, density 0.92 [gcm.sup.-3], JIS-A hardness 50, tensile strength 13.1 MPa with 440% elongation and melt flow rate (MFR) [230[degrees]C, 2.16 kg] 8.4 g/10 min) was obtained courtesy of Kaneka Corporation, Osaka, Japan. SIS (grade D1107, 15 wt% polystyrene, density 0.95 [gcm.sup.-3], Shore A hardness 32) and SBS (grade D1102, 28 wt% polystyrene, density 0.88 [gcm.sup.-3], Shore A hardness 66) were obtained courtesy of Kraton Polymers, Houston, Texas, USA. NR, pale crepe (grade SMR CV50, Mooney viscosity [M[L.sub.1+4], 80[degrees]C] 50) was obtained courtesy of Ashland Rubber Inc., Oakville, Ontario, Canada.

Iron powder (grade Atomet 67, 71.4% of 100 to +325 U.S. Mesh and 23.2% of 325 U.S. Mesh, density 7,800 [gcm.sup.-3]) was obtained from Quebec Metal Powders Limited.

Polymer Blending

All blends were prepared in a laboratory internal mixer (Haake Rheocord model "Rheomix 3000") with cam-type rotors operating at 35 rpm at 160 [+ or -] 10[degrees]C. First, the block copolymer was added and allowed to soften for 2 minutes. Then, the elastomer was added and mixed for another 2 minutes before the addition of the iron powder, and mixing was continued for another 5 minutes.

Polymer and Composite Characterization

Compression molding of test specimens was carried out in an electrically heated hydraulic press at a pressure of 3.5 MPa and 166[degrees]C for 30 minutes. The die was then air cooled to room temperature before removing the sample to prevent puncture or deformation.

Hardness measurements were carried out using an Instron Model 902 Shore A durometer with a conical indenter (ASTM D 2240) on 6-mm-thick compression molded sheets.

Compression creep behavior was analyzed using a Haake DEFO-Elastomer instrument, by applying a constant load (75 N) to a compression molded cylindrical specimen (10-mm diameter and 10-mm height) at 40[degrees]C and measuring the change in sample height for 30 minutes.

Dynamic mechanical analysis (DMA) in compression was carried out using an MTS 831 Elastomer Test System (MTS Systems Corporation, USA) on compression-molded cylindrical specimens (10-mm diameter and 10 mm-height) under a static strain of 7% with 3% dynamic strain. Frequency sweeps (0.01-500 Hz) were carried out at 50, 0, and -50[degrees]C. Temperature sweeps (-100 to 100[degrees]C) were obtained at 10 Hz using a GABO EPLEXOR145, with 2[degrees]C/min heating rate.

Differential scanning calorimetry (DSC) was carried out using a TA Instruments 2920 Modulated DSC model at a heating rate of 10[degrees]C/min. [T.sub.g] values were measured in the second heating cycle after normalizing thermal history.

Scanning electron microscopy (SEM) analysis was carried out with a JEOL JSM 848 instrument using 15-kV beam energy on specimens fractured in liquid nitrogen and sputtered with 13-nm gold coating.


SIBS/IIR/Iron Composites

Dynamic Mechanical Thermal Analysis (DMTA) Analysis. As discussed in the Introduction, we recently reported that the 50:50 blend of IIR and SIBS with 233 parts of iron powder was suitable for the preparation of novel LLA [10]. The blends included in the comparative analysis are shown in Table 1.

The density of all blends met the minimum density requirement of 2.4 [gcm.sup.-3] [10]. It was shown that the performance of this new highly-filled elastomer-TPE composite satisfied the requirements for this specialty application in terms of shape retention characterized by compression creep, and energy transfer on impact characterized by moduli and damping characteristics. Figure 2a and b presents the temperature sweeps. The moduli profiles of all the composites shown in Fig. 2a are very similar, with the indication of two broad low-temperature transitions. The tan[delta] plot of the IIR/iron composite (with no SIBS) in Fig. 2b shows two broad but distinctly different transitions. In comparison, unfilled IIR (RB301) and PIB had a single, broad, low-temperature transition under similar test conditions [24]. Broad low-temperature transitions are characteristic of IIR and PIB, which were shown to exhibit three relaxation processes in the glassy-rubbery transition [25, 26], each of which can be associated with a cluster of different rigidity and structural order [27]. At the same time, DSC showed practically identical glass transition temperature, [T.sub.g] (-68[degrees]C) for IIR and IIR/iron. The low-temperature (-60[degrees]C) transition of the IIR/iron composite in Fig. 2b can be assigned to the "regular" IIR or PIB [T.sub.g]. The broad transition at around -20[degrees]C can be associated with the transition of IIR or PIB chains restricted by polymer-filler interaction. It is interesting that the -20[degrees]C peak is larger than the -60[degrees]C peak. A similar phenomenon is well-known for IIR/carbon-black composites; DMA shows two transitions while DSC indicates a single [T.sub.g] for both neat IIR and IIR/black [2].


The SIBS/IIR/iron composites also display two distinct broad transitions, with the -20[degrees]C peak always being larger than the -60[degrees]C peak. The area under the -60[degrees]C peak decreases with increasing SIBS content, which demonstrates increasing restriction of the butyl and PIB chains by the SIBS network structure. The -20[degrees]C transitions are very similar to each other and the IIR/iron composite, thus we believe that they represent some kind of interaction between the iron filler and the butyl and PIB chains, restricting their mobility. On the other hand, the Shore A hardness of the highly-filled composites would indicate no or very weak polymer-filler interaction. This apparent contradiction should be further investigated. SEM analysis of SIBS50 revealed encapsulation of the iron particles by the continuous rubber phase, as shown in Fig. 3. Hard polystyrene (PS) phases at the nanometer scale, also distributed in the continuous rubber phase, can also be discerned in the pictures. It is reasonable to consider restriction of the rubber chains in the vicinity of the iron particles and the PS phase, accounting for the higher-temperature DMA transition. Table 1 demonstrates that the Shore A hardness increases with the addition of SIBS, which was explained with the introduction of hard amorphous styrenic domains into the continuous soft elastomeric phase. The IIR/iron composite with no SIBS has very low Shore A hardness, in spite of the high filler loading. The Shore A hardness of the existing less-lethal projectiles investigated (see Fig. 1) was in the range of 60-85 (with the exception of the monoball). It is interesting to note that even the SIBS/iron composite mix had lower Shore A hardness than existing ammunition (Table 1). Softer composites are expected to be better suited for LLA; hardness was one of the important criteria for the optimization and analysis of less-lethal projectiles [10]. However, hardness, which can be regarded as a single-point stiffness measurement, can hardly give an idea of the performance of these projectiles under realistic conditions. Less-lethal projectiles are normally fired at a velocity of about 250 ft/sec (~75 m/sec), thus the estimated frequency range of the deformation upon impact is estimated to be about 16,000 to 21,000 Hz (~102,000 to 132,000 rad/sec). Hence, we thought that stiffness analysis in a wide frequency range (dynamic stiffness) should be a better way to compare the performance of various less-lethal projectiles.


Dynamic Stiffness Analysis. High frequency dynamic mechanical analyzers are very commonly used in the tire industry to evaluate the performance of the elastomer-based composites at high velocity. Another approach is the TTS, which has been applied to block-type TPEs [28] and filled butyl rubber [29], but is normally believed to be inapplicable to highly-filled systems. TTS was applied using the frequency sweeps at -50, 0, and 50[degrees]C and the Williams-Landel-Ferry (WLF) method (IRIS-7 software [30]). The master curve obtained for SIBS50 and the log shift factor ([a.sub.T]) vs. 1/T plots for all composites are shown in Fig. 4a and b, respectively.

Although only three temperature sweeps were available to construct the master curves, the near linearity of the log([a.sub.T]) - 1/T plots indicate that TTS could be used for the stiffness analysis. Table 2 lists the WLF constants together with the Vogel-Fulcher (VF) constants calculated as b = 2.303[C.sub.1][C.sub.2] and [T.sub.[infinity]] = [T.sub.0] - [C.sub.2] (31). Interestingly, the VF constants for SIBS50 are very close to those published earlier for linear and branched PIB [30-34].

The stiffness function is defined by Eq. 1

S([omega]) = [G'([omega])]/[[[omega].sup.2[delta]/[pi]]cos[delta][GAMMA](1 - 2[delta]/[pi])]. (1)

This can be related to materials at the critical gel point. According to Winter and to Chambon, the complex modulus follows a power law in the entire frequency region at the critical gel point ([p.sub.c]) [35-37].


G*([omega],[p.sub.c]) = [GAMMA](1 - n)S(i[omega])[.sup.n] (2)

where [GAMMA](1 - n) is the gamma function, S is the strength of the network at the critical gel point, and n is the relaxation exponent. The relaxation exponent may have values in the range of 0 < n < 1, depending on the molecular architecture. At the critical gel point the stiffness is independent of frequency. Visualizing the blends as a network held together by the labile cross-links of the SIBS, one can attempt to apply Eq. 1. Indeed, the labile nature of this type of "crosslink" was demonstrated for hydrogenated polystyrene-b-polybutadiene-b-poly(methyl methacrylate) (SBM) triblock terpolymers; the master curve constructed from frequency sweeps at an amplitude of 1% shows network behavior with no crossover between storage (G') and loss shear moduli (G"), while at an amplitude of 20% the network is disrupted enough to cause the blocks to respond like a linear polymer with a crossover between G' and G" [28].


Figure 5 shows the stiffness plots for the SIBS/IIR composites. IIR, SIBS25, and SIBS75 have similar profiles, with the IIR composite showing the lowest values in the whole range. In contrast, SIBS50 showed the lowest stiffness up to about [10.sup.6] rad/sec, above which it had the highest stiffness of all the composites. In the frequency range of interest for the LLA application (~102,000 to 132,000 rad/sec) the dynamic stiffness of SIBS50 is the lowest and independent of frequency. The reason for this interesting behavior is unknown at this time and requires further investigation. Based on the VF constants listed in Table 2, one can theorize that a continuous butyl rubber phase dominates the dynamic response of this composite.

Other TPE/Elastomer/Iron Composites

DMTA Analysis. The performance of the iron-filled SIBS/IIR 50/50, i.e., SIBS50, blend was compared with other composites. Table 3 shows the composites included in the comparative study. The composites had nearly identical densities, reaching the minimum required 2.40 [gcm.sup.-3]. The SIBS/NR/iron composite was softer than the SIBS/IIR/iron composite, while the SBS/NR/iron composite was significantly harder and the SIS/NR/iron composite was extremely soft. SIS had less PS and was softer than the other TPEs, and this latter blend was a sticky, gluey substance as it was removed from the mixer--degradation most likely occurred during mixing. Thus, this blend showed extremely high-compression creep, in comparison with the other blends shown in Fig. 6. The compression creep behavior of the blends scales with their softness; SIBS/NR/iron shows the highest deformation at 23%, with SIBS/IIR/iron and SBS/NR/iron showing 12% and 6% under the same testing conditions. In comparison, iron-filled SIBS showed 4% deformation [10]. The similarly low creep of SBS/NR/iron could be due to the occurrence of branching (grafting) or cross-linking reactions, catalyzed by iron [9, 38].


Figure 7a and b compares the temperature dependence of the dynamic mechanical properties of the various filled TPE-elastomer blends. The tan[delta] plot of SBS/NR/iron shows a low transition at -80[degrees]C (Fig. 7b), assigned to the polybutadiene, while the other sharp transition at -50[degrees]C can be assigned to the NR. SIS/NR/iron shows only one transition as expected, while SIBS/NR/iron and SIBS/IIR/iron show two transitions with more pronounced and broader change for the latter. The plateau occurs at around -40[degrees]C for SBS/NR/iron, -30[degrees]C for SIS/NR/iron, and 0[degrees]C for SIBS/NR/iron and SIBS/IIR/iron. At temperatures above 0[degrees]C, SBS/NR/iron shows higher moduli values than the other blends that display similar values.


The SIBS/IIR/iron composite shows two tan[delta] peaks at -60 and -20[degrees]C, similar to those seen in Fig. 2b. The SIBS/NR/iron also shows double peaks, but the -20[degrees]C peak is much smaller than that for the SIBS/IIR/iron. In the case of the SIBS/NR/iron the -20[degrees]C transition might be construed as an indication of branching/cross-linking in the NR phase, catalyzed by iron, which would restrict segmental motion. However, this would be in contradiction with the creep measurement data that showed high creep for SIBS/NR/iron (Fig. 5). Considering this apparent contradiction, we could conclude that the iron catalyzes both branching/cross-linking and degradation of the NR phase. The higher moduli of the SBS/NR above -40[degrees]C (see Fig. 7a) further supports this proposition--in this case, intermolecular cross-linking between the polybutadiene blocks of the SBS and the NR could also occur, resulting in high modulus and low creep. The SBS/NR/iron composite also shows two tan[delta] peaks; a small one at -80[degrees]C and a larger one at -50[degrees]C. The former can be assigned to the polybutadiene blocks of the SBS, and the latter to the NR phase [9]. The position of this peak coincides with the single transition of the SIS/NR/iron composite.


Based on the DMA analysis, some type of restriction of the elastomer by the filler is evidenced in SIBS/IIR/iron and SIBS/NR/iron, while other composites did not show interaction. This phenomenon should be investigated further.

Dynamic Stiffness Analysis. Dynamic stiffness analysis was also carried out for the TPE/elastomer composites using TTS. The log([a.sub.T]) - 1/T plots were close to linear, and Table 4 lists the WLF and VF constants.

Figure 8 shows the stiffness plots. The stiffness of SIBS/IIR/iron is the lowest in the lower frequency range, with SBS/NR/iron displaying quite higher values. It is also apparent that, with the exception of SBS/NR/iron (gradually decreasing stiffness with frequency), the stiffness of the composites is independent of frequency below about 2 X [10.sup.5] rad/sec, with an abrupt change occurring between [10.sup.5] and [10.sup.6] rad/sec. The stiffness sharply drops for SIS/NR/iron, while it sharply increases for SIBS/NR/iron. SIBS/NR/iron shows the lowest stiffness below 2 X [10.sup.5] rad/sec, and the highest above [10.sup.6] rad/sec. The reason for this behavior is not clear at this time. However, the stiffness analysis supports the results of impact testing reported in Ref. 10, showing that the SIBS/NR/iron composite is well-suited less lethal projectiles.


The stiffness of SIBS/IIR/iron 50/50/233 was also compared to that of the existing less lethal ammunitions shown in Fig. 1. The stiffness plots are displayed in Fig. 9. Note that the frequency range in Fig. 9 is different from that of Figs. 4 and 8, since due to hardening of the specimens it was not possible to test the rocket and tube projectiles at lower temperatures needed to extend the range to higher frequencies (>[10.sup.6] rad/sec). However, this frequency range was still in the estimated firing frequency range for these projectiles. Above [10.sup.2] rad/sec, the SIBS/IIR/iron showed much lower stiffness than the commercial LLAs--within the estimated firing frequency range the difference is 2-3 orders of magnitude. Therefore, the new SIBS/IIR composite is expected to have superior performance compared to existing LLAs.

A prototype novel LLA ("Wasp") was produced and successfully tested using the 3-rib model by Bir et al. [23]; the results will be published elsewhere.


In conclusion, a newly developed IIR/SIBS/iron 50/50/233 composite showed unique performance in dynamic applications such as LLA. In comparison with other compositions, it displayed frequency-independent minimum stiffness in the desired range. DMTA analysis showed two low-temperature transitions for IIR/iron and other composites containing SIBS. This indicates limited mobility of the rubber phase in the vicinity of the iron filler and/or PS discreet phases. This phenomenon was not seen in ironfilled SIS/NR or SBS/NR composites. SIBSS50 showed much lower stiffness than existing less lethal ammunition.
TABLE 1. Composition, Shore A hardness, and density of various IIR/SIBS/
iron composites.

 Composite designation
Ingredients (a) IIR SIBS25 SIBS50 SIBS75 SIBS100

IIR 100 75 50 25 0
SIBS 0 25 50 75 100
Iron powder 233 233 233 233 233
Compression creep, % 32 22 12 11 4
Shore A hardness 19 23 36 44 53
Density, [gcm.sup.-3] 2.40 2.42 2.44 2.46 2.49

(a) Compositions are in part per weight.

TABLE 2. WLF ([C.sub.1], [C.sub.2]) and VF (B, [T.sub.z]) constants for
SIBS/IIR/iron composites, [T.sub.0] = 273.15 K.

Sample [C.sub.1] [C.sub.2] (K) b [T.sub.[infinity]] (K) Ref.

IIR 10.19 181.81 4772.36 91.34 [31]
PIB 8.65 159.15 3170 114 [31]
 8.79 159.15 3220 114 [32]
 8.96 151.15 3120 122 [33]
 8.60 167.15 3310 106 [34]
SIBS25 11.20 195.95 5932.52 43.15
SIBS50 8.65 170.80 3402.50 102.35
SIBS75 13.50 230.00 6092.18 77.20
SIBS 11.14 203.36 4648.25 91.97

TABLE 3. Characteristic data for highly-filled TPE/elastomer/iron
50/50/233 blends.

Blend designations

Density ([gcm.sup.-3]) 2.41 2.40 2.41 2.44
Shore A hardness
 TPE 54 32 66 53
 Composite 30.4 19.9 47.8 36
Compr. creep, % 23 -- 6 12

TABLE 4. WLF and Vogel-Fulcher constants for TPE/elastomer/iron
composites, [T.sub.0] = 273.15 K.

 [C.sub.1] [C.sub.2] (K) [T.sub.0] (K) b

SIBS 8.65 170.80 273.15 3402.50
SIS/NR 9.55 218.71 273.15 4810.23
SIBS/NR 11.88 212.67 273.15 5818.57
SBS/NR 15.68 203.23 273.15 7338.85
NR (32) (a) 8.86 101.6 248 2070.4

 [T.sub.[infinity]] (K)

SIBS 102.35
SIS/NR 54.44
SIBS/NR 60.48
SBS/NR 69.92
NR (32) (a) 146.4

(a) [T.sub.0] = 248 K.


We thank Jon Bielby of Lanxess Inc. in Sarnia, Ontario for providing the butyl samples and helping us with the DMA measurements; Elizabeth Takacs of the Centre for Advanced Polymer Processing and Design, McMaster University, Hamilton, Ontario for her assistance in the preparation of blends; and Anne Lang for SEM analyses. Useful discussions with and advice from Prof. H. Winter is also acknowledged.

Presented at the Meeting of the Polymer Processing Society (PPS), Akron, Ohio, June 20-24, 2004.

Contract grant sponsors: Materials and Manufacturing Ontario (MMO); Pine Tree Law Enforcement Products of Canada Ltd.

BR butadiene rubber
EPDM terpolymer of ethylene, propylene and a diene
PIB polyisobutylene
IIR isobutylene-isoprene rubber (butyl rubber)
IR isoprene rubber
JIS-A hardness Japanese Institute of Standards (JIS K6301); 0 to 100
LLA less-lethal ammunition
SBR styrene-butadiene rubber
SBS poly(styrene-b-butadiene-b-styrene) block copolymer
SIBS poly(styrene-b-isobutylene-b-styrene) block copolymer
SIS poly (styrene-b-isoprene-b-styrene) block copolymer
TPE thermoplastic elastomer
TTS time-temperature superposition
VF Vogel-Fulcher
WLF Williams-Landel-Ferry


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Judit E. Puskas

Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909

Bhuwneesh Kumar, Amer Ebied

Department of Chemical and Biochemical Engineering, The University of Western Ontario, London, Ontario N6A 5B9, Canada

Barry Lamperd

Pine Tree Law Enforcement Products of Canada Ltd., 1200 Michener Road, Sarnia, Ontario N7S 4B1, Canada

Gabor Kaszas

Lanxess Inc., 1265 Vidal St. South, Sarnia, Ontario N7T 7M2, Canada

Jan Sandler, Volker Altstadt

Department of Polymer Engineering, University of Bayreuth, Universitatsstr. 30, 95440 Bayreuth, Germany

Correspondence to: J.E. Puskas, e-mail:
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Author:Puskas, Judit E.; Kumar, Bhuwneesh; Ebied, Amer; Lamperd, Barry; Kaszas, Gabor; Sandler, Jan; Altsta
Publication:Polymer Engineering and Science
Geographic Code:1CANA
Date:Jul 1, 2005
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