Blending of Poly Aramid by Plasticization

Idea of Poly Aramid blending

The plasticization of Poly aramid was carried out in four stages, which are:

1. Synthesis of Aramid
2. Synthesis of Hyperbranched Polyamide-ester HBPA
3. Synthesis of Stock Solutions
4. Blending of Aramid and HBPA

Synthesis of Poly Aramid

Method

For studying Aramid in detail, follow Aramid processing and Aramid applications. Aramid have wide range of applications in form of KEVLAR fibers and TWARON fiber properties.

In present study, we tried to share our research where we synthesized Aramids by polycondensation process.

Poly Aramid was synthesized by the polycondensation reaction of a diacid chloride with a diamine monomer. A known amount (0.000625M) of m-phenylenediamine and (0.00025M) 4,4¢-oxydianiline powders were placed in flask followed by the addition of 10 mL N,N-dimethylacetamide at room temperature with continuous stirring. The solution was stirred for 8 hours for making a homogenized mixture. After mixing of diamines appropriate amount (0.0025M) of isophthythl chloride was added to this solution with continuous stirring. This reaction is very exothermic so cooling in an ice bath, maintained at 0oC, was provided to avoid any side reactions.

The whole solution was stirred again for 6 hours to allow the monomers to polymerize properly. The HCl produced during polymerization process along with the DMAc provided desired salt-solvent combination which increased the solvating power of the solvent as the molecular weight build-up. The reaction mixture obtained after completion of polymerization was highly viscous and dark brown in color. A film and membrane of aramid were obtained by treating the solution in two ways:

• When the solution gained high molecular weight due to polymerization, some of its amounts were poured into a Petri dish and put into a vacuum oven at 100oC temperature for 12 hours. A brown and slightly transparent film of the aramid was obtained as a result of heating (Fig. 02).
• Water was added into the remaining polymerized solution when a white membrane was obtained (Fig. 03), excess water was removed and dried.

Reaction Mechanism

A diamine was reacted with diacid halide using solution polymerization route for poly aramid synthesis. N,N-Dimethylacetamide was the solvent used for dissolving the monomers and providing medium of reaction. An ether containing diamine was used as it provides more flexibility and solubility along with another aromatic diamine which provides stiffness. Equal proportion of both diamines linked C=O of diacid halide with NH group of amine to make the amide linkage.

Five different proportions of monomers were used and prepared to form a film of aramid using the above mentioned process (Table 01). The film and membrane formation were seen when 50%: 50% and 100% of diamines and dichloride monomers were used, respectively.

Synthesis of Hyperbranched Polyamide-Ester (HBPAE)

Method

Hyper branched polymers are widely used because of their low viscosity and easy processability. They are usually combined with Aramids to improve certain processing of Aramids. Follow Hyper branched polymers for detail understanding of their true nature.

Hyperbranched polyamide-ester (HBPAE) was prepared by the polycondensation reaction between a trifunctional and a bifunctional monomer. Desired amount (0.0035M) of 4-hydroxy-2,6-diaminopyrimidine (HDAP) powder was added into 10 mL of N,N-dimethylacetamide solvent with continuous stirring and heating using hot plate magnetic stirrer.

The solution was stirred and heated until the powder was dissolved and transparent solution was obtained. Then 0.0035M isophthythl chloride was added into the transparent solution with continuous stirring for homogenous polymerization. After stirring for 4 hours the solution was poured into a Petri dish and placed in a vacuum oven for 8 hours at 80^oC, for heating and evaporation of solution. As a result a yellow powder of hyperbranched polymer was obtained.

Synthesis

 4-Hydroxy-2,6-diaminopyrimidine was used as CBB’ type monomer and diacid chloride was added as A₂ type monomer. CBB’ monomer of unequal reactivity was used to prepare HBPAEs without gelation contrary to the classical A₂+B₃ methods (Fig. 04). In this regard A₂ monomer was added in molar excess to CBB’ monomer, the excess A₂ limited the increase in molecular weight avoiding the risk of gelation.

The amine group at 2-position is less reactive as electronegative nitrogen atoms are present in pyrimidine ring than amine group at 6-position due to electron-withdrawing inductive effect of heteroatom (N). Consequently, the lower reactivity of 2-amine group than the 6-amine group in HDAP resulted in no gelation during the polymerization. Besides this the nucleophilic reactivity of the amine group is known to be much greater than that of the hydroxyl group.

Hence, there is a less steric hindrance for amine of this trifunctional monomer at 6-position, the reactivity sequence of different groups is as follows; 6 amines (B’)> 2 amines (B)>4 OH (C). The reactivity sequence of CBB’ monomer can be responsible for the polymerization of 2A2+CBB’. At the initial stage of the reaction amine at 6-position reacts with A₂ at 0^oC, resulting in the formation of ABC type precursor, then A₂ left as residue reacts with an amine on 2-position at the same temperature, forming A₂C type intermediate and finally in situ polymerization of A₂C results in the formation of HBPAEs at 30^oC.

The HBPAE was then poured into a Petri dish and placed in vacuum oven for 8 hours at 80^oC, for evaporation of solvent. As a result of drying a yellow powder of hyperbranched polymer was obtained.

Synthesis of Stock Solution

The stock solution of poly aramid and hyperbranched polymer was prepared for making 11 different blend compositions. For the preparation of aramid stock solution the method mentioned in above for aramid synthesis was repeated. The only difference was that when the polymerization was completed 1% excess diamines was added to obtain an amine terminated aramid.

Amine terminated aramid stock solution was prepared so as to blend it with COCl terminated hyperbranched polymer. The stock of hyperbranched polymer was prepared repeating the same steps mentioned above in the synthesis of hyperbranched polymer but the only difference was in amount of monomers and solvent (30 mL of N,N-dimethylacetamide).

Blending of Poly Aramid and Polyamide – ester

After preparation of the stock solutions blends of 11 different compositions were prepared (Table 02.). Aramid and hyperbranched polymer solutions were added into one another by taking 10 different proportions and continuous stirring. These solutions were stirred for 8 hours continuously using magnetic stirrers to obtain a homogeneous mixture.

The obtained blend solutions were then heated to evaporate the solvent. Heating was done in a vacuum oven at 80^oC for 12 hours. Blends of 90%, 80%, 70%, 60%, and 50% poly aramid showed film formation upon heating.

Precautions and Conditions for Synthesis for Poly Aramid

During the synthesis of poly aramid and hyperbranched polymer certain precautions were also taken into account. The reaction conditions were controlled in order to obtain pure and completely polymerized polymers. These conditions were:

• An extremely clean and dried apparatus was used to avoid the incorporation of moisture and impurities.
• The complete absence of moisture as it can cause swelling of polymer films and lower the desired mechanical and thermal properties.
• Continuous stirring was provided during the mixing and dissolution of monomers to make a homogenously polymerized and blended polymer.
• Heating in a vacuum oven to avoid impurities which may deteriorate the properties of the polymer.
• Proper heating at the optimum temperature (100oC) was provided for a specific time to prepare polymer films.

References

Handbook of Plasticizers – Book For Polymer explorers