Sulfur styrene modified

Figure 4. Gel permeation chromatograms of the styrene-modified sulfur materials. Samples are identified by percentage of styrene used (w/w sulfur) and heating time at 140°C. (a)...

Sulfur Concrete Modified with Styrene. If styrene is added to sulfur melts, the viscosity rises to a maximum within a few minutes irrespective of the styrene concentration (Figure 9). After reaching the maximum value, the viscosity decreases steadily to a constant final value which depends on the amount of styrene added. This characteristic behavior may be caused by thermal polymerization of the styrene followed by degradation of the polymer by reaction with sulfur. 

The use of styrene to modify sulfur melts and thus to improve the binder properties was unsuccessful. When producing sulfur binder modified with styrene, reaction times of at least 1.5 hr at 140°C were used, since by then the viscosity maximum had been passed and a constant viscosity value had been reached. Sulfur melts plasticized by... 

In examining the strength properties of sulfur concrete modified with styrene, the compressive strength was insufficient and worse than in the case of unmodified sulfur concrete (Table VI). After 70 days storage, however, the compressive strength of the test samples modified with 10 wt % styrene increased to 432 kp/cm2, which is an average of 46%. The increase in the test samples modified with 5 wt % styrene was 4%, corresponding to a value of 526 kp/cm2. 

Of the various chemical modifiers for sulfur which we have examined over the years we must single out the Thiokol family of additives as some of the most effective sulfur modifiers available (10). Unfortunately they are expensive, but their effects are long term. One of the most deceptive of the sulfur additives is styrene monomer (JJ) which is attractive because of its low cost. One can obtain an unusually wide variation of properties in sulfur-styrene mixtures by controlling the degree of reaction. Unfortunately these property modifications are transient, so much so that we use it infrequently and for only some special purpose. The transient characteristics of styrene-sulfur mixtures are attributed to the attack of the polystyryl radicals on the sulfur-sulfur bonds and the rapid opening of the sulfur rings. 

Compressive strength (Figure 6) of sulfur has a very high initial figure falling to a level at about 7000 kNm 2. The modified materials have much lower values, which with the lower levels of additive (5 and 10% styrene), increase rapidly after approximately two weeks, presum-... 

Figure 5. Shore D hardness vs. log time plots of modified sulfur materials. Samples are identified by percentage of modifier used (w/w sulfur) and heating time at 140°C. The onset of sample shattering is indicated by X. (a) Sulfur (b) 5% dicyclo-pentadiene, 3 hr (c) 10% dicyclopentadiene, 3 hr (d) 25% dicyclopentadiene, 3 hr (e) 5% styrene, 3 hr (f) 10% styrene, 3 hr (g) 25% styrene, 3 hr (h) 25% myrcene, 0.8 hr.

Since plasticized sulfur has better mechanical properties than elementary sulfur, the properties of sulfur modified with styrene or dicyclo-pentadiene (DCP) as binder for aggregates were examined. These modifiers seemed to be the most favorable because of both improvement in properties and low price. Furthermore, as stated in the literature, DCP-modified sulfur has a lower combustibility (15). 

Dicyclopentadiene, dipentene, styrene, CTLA polymer, and methyl-cyclopentadiene dimer were used as modifiers. These modifiers are all available in commercial quantities at 5-12 cents/lb. All contain unsaturated double bonds suitable for direct reaction with sulfur. The materials used in this investigation were from the following sources ... 

Laboratory Reaction Tests. It was necessary to understand the reaction parameters for the modifiers dipentene, styrene, and dicyclopentadiene to aid future field stabilization tests. Laboratory tests were performed to define the typical character of the material in the liquid and solid state. The conditions necessary to form completely plastic noncrystalline sulfur with each modifier were also established. 

In general, sulfur penetration into soil test specimens depended on both temperature and modifier concentration. Using styrene or dicyclo-... 

Sulfur can be fully plasticized by using the modifiers dipentene, styrene, and dicyclopentadiene. Sulfur can be plasticized with dicyclo-pentadiene at two minimum concentrations, as indicated in Table III 13% at reaction temperatures of < 140°C and 6% at reaction temperatures > 140 °C. This effect probably results from cracking of the dicyclopentadiene dimer molecule, which doubles the molecules available for reaction. The higher percentage dicyclopentadiene mixture was initially flexible. Upon aging, both plasticized materials became brittle. The reaction is exothermic and very difficult to control above 140 °C. When uncontrolled, extreme viscosity increases were encountered. 

We have tried to increase the reactivity of modified polystyrene by introducing sulphur bonds with small dissociation energy into its macromolecules. For that purpose we carried out styrene polymerization with tetramethylthiuram disulphide in the presence of sulfur as an initiator. The chemical composition of modified polystyrene was as follows 83.02% C, 7.28% H, 1.07% N, 7.91% S (Table 1). As acconsequence of the addition of sulfur to the reaction medium the sulfur/nitrogen mole ratio increased from 2 1 to above 3 1. The average molecula weight of po lystyrene modified by thiuram and sulfur was low, Mv = 2030 and = 2080. 

Sulfur cure systems are well known to be complex in their reactions and in the types of cross-links they produce. There is general agreement that if sulfur alone is used to vulcanize a rubber, most of the cross-links will have more than two sulfur atoms in themW. These polysulfides are less stable than monosulfides or disulfides. This phenomenon has been examined in some vulcanized elastomers by using chemical probes, which modify or break only certain kinds of cross-links CDW(. Parel elastomer is more difficult to study in this fashion than styrene-butadiene rubber (SBR) or natural rubber because many of these chemical reagents also react with the C-0 bonds of the polyether. 

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