Mechanical properties of HTPB-IPDI-based elastomers

A polyurethane elastomer having mechanical and adhesive properties suitable for liner applications in solid rocket propellants was developed using HTPB as the prepolymer and IPDI as the curing agent. The effects of the NCO/OH ratio (R value) and the trio/diol ratio on the mechanical properties of the polyurethane matrix were investigated. The reaction of HTPB and IPDI is followed by monitoring the changes in the IR absorption bands of the NCO stretching at 2255 cm⁻¹ and the CO stretching at 1730 cm⁻¹. It was found that the rate of the polyurethane formation obeys an overall second-order kinetics. At an R value of 1.15, the elastomer shows the maximum tensile strength and 200% elongation at break. The hardness, elongation, and the tensile strength reach a steady value around the same R value. The elastomers having a triol/diol ratio less than 0.03 show a decrease in the tensile strength and modulus with a concomitant increase in elongation. At a triol/diol ratio greater than 0.05, the tensile strength increases to about the same value for the liner composition without any triol component. The elongation reaches a steady level at a triol/diol ratio of 0.10 and one observes a steady increase in hardness up to 0.5. The modulus for the compositions having a triol/diol ratio greater than 0.1 is about 50% higher than that for the composition without triol. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2347–2354, 1997     

Purification and Properties of the Raw Starch Digesting Amylase from Penicillium brunneum No. 24

Raw sago starch digesting amylase was obtained from Penicillium brunneum No. 24. The crude enzyme from this strain contains carboxymethylcellulase (CMC-ase), avicelase, α-amylase and α-glucosidase. Affinity chromatography (α-cyclodextrin-Sepharose 6B) of the enzyme after ammonium sulfate fractionation, Toyopearl HW-55F gel filtration, DEAE-Sephadex A-50 and DEAE-cellulose chromatographies fractionation steps, resulted in a homogeneous glucoamylase. SDS-polyacrylamide gel electrophoresis of purified enzyme showed a single band, and a molecular weight of 80,000 for the native glucoamylase from Penicillium brunneum No. 24 was observed. After modification of the native glucoamylase with subtilisin, the molecular weight was reduced to 76,000. It lost the ability to digest and adsorb onto raw starches. However, its ability to digest gelatinized starches was preserved.     

Glucose Production from Treated Sago Starch Granules by Raw Starch Digesting Amylase from Penicillium brunneum

Several microorganisms have been found to produce raw starch digesting amylase. We have isolated Penicillium brunneum from sago palm tree at a sago processing site, which was used as a source of starch digesting amylase. All the raw starch digesting enzymes were effective for cereal starches, but root starches and sago starch were resistant to the enzyme reaction. Treatment of sago starch by heating to temperature below gelatinization temperature at lower pHs resulted in an increase in the ability of enzyme to digest sago starch granules. Heating to 60°C at pH 2.0 resulted in a conversion rate of sago starch granules to glucose near to the conversion rate of raw corn starch to glucose. At higher concentration, the degree of hydrolysis of treated sago starch granules was about 275% as compared to that of untreated sago starch granules. Addition of the enzyme in large amount or small portion at various time intervals was found effective in the hydrolysis of treated sago starch granules.     

Mechanism of Hydrolysis of the Treated Sago Starch Granules by Raw Starch Digesting Amylase from Penicillium brunneum

We have prepared raw starch digesting amylase from Penicillium brunneum, which is similar to other raw starch digesting enzymes, and is effective in hydrolyzing raw cereal starches, but not effective for raw sago starch and raw root starches. Treatment of sago starch granules before incubation with the enzyme by heating to below gelatinization temperature at low pH condition was effective in improving the hydrolysis. Observation by scanning electron microscope showed that structure of treated sago starch granules at 60°C pH 2.0 for 2h was not changed. Observation under polarized light showed the birefringence clearly was preserved. However, viscosity of treated sago starch granules decreased. After incubation with the enzyme, untreated starch granules corroded and several holes were seen on the surface of granule. Enzyme action on the treated starch granules resulted in much higher intensity of degradation and the holes deepened into the interior of granules. Analysis of the product of this process showed that mainly glucose was produced from the hydrolysis of treated or untreated sago starch granules by crude enzyme. But on gelatinized sago starch other types of sugars were formed during enzyme reaction.     

Effect of Cellulase Addition on Hydrolysis of Sago Starch Granules by Raw Starch Digesting Amylase from Penicillium brunneum No. 24

Raw sago starch digesting amylase was obtained from Penicillium brunneum No. 24. with strong ability to digest sago starch granules. The crude enzyme from this strain contains CMC-ase and avicelase. The specific activity of the enzyme did not increase proportionally with purification. We tried combination of our purified enzyme with other hydrolytic enzymes as a means of improving the hydrolysis of sago starch granules. Addition of cellulase at the initial stage of the hydrolyzation process resulted in an increase in the ability of raw starch digesting amylase to digest sago starch granules. Adding 10 unit/g starch of cellulase. followed of our purified raw starch digesting amylase in small portion at various time intervals was found effective in the hydrolysis of untreated sago starch granules. The treatment resulted in a convertion rate of untreated sago starch granules to glucose near to complete after 120h enzymes reaction, and was also effective in reducing the reaction time of hydrolysis of treated sago starch granules. This process showed that mainly glucose was produced.