Polymers and plasticizers

Polymers

Polymers play an important role of a binder in solid propellant and plastic explosives. Fuel, high energy or explosive material is dispersed in a polymer matrix, which binds all the ingredients together. Most popular group of polymers are polyurethane binders, which are based on HTPB pre-polymer or its derivatives. Production process of solid propellant includes mixing energetic material with pre-polymer, cross-linking agent and additives such as plasticizers, casting mixture into a mold and cross-linking of the pre-polymer. Desired physicochemical properties of the product may be optimized by careful choice of the ingredients.

NHTPB
NHTPB is a derivative of HTPB that contains high-energy nitrate groups in its structure. Advantages: – The low viscosity of NHTPB makes it a good high-energy binder that, compared to HTPB, allows the introduction of more solids and improved miscibility with other ingredients. – propellants containing NHTPB are about 3-5% higher in energy than HTPB – NHTPB increases the decomposition temperature of the propellant – small addition of NHTPB to HTPB, about 2%, allows to improve ballistic properties and to increase energy
Enthalpy of formation	-442 kcal/mol
Decomposition temperature	206°C
Glass transition temperature	-58°C
Density	1.2 g/cm³

Nitro HTPB
Nitro-HTPB is a derivative of HTPB that contains high-energy nitro groups in its structure. Advantages: – higher energy of the polymer compared to HTPB – better miscibility with energetic plasticizers – good mechanical properties – higher thermal stability compared to NHTPB
Enthalpy of formation	No data
Decomposition temperature	No data
Glass transition temperature	-64°C
Density	1.25 g/cm3

GAP
Glycidyl polyazide is an energetic polymer containing azide groups in its structure. It is used to increase the calorific value of solid fuels. Advantages: – low sensitivity to thermal and mechanical stimuli – high energy content – low glass transition temperature – low viscosity and high density compared to other binders – high compatibility with various oxidants
Enthalpy of formation	27.86 kcal/mol
Decomposition temperature	224°C
Glass transition temperature	-121°C
Density	1.29 g/cm³

Block copolymers GAP – PB – GAP

GAP – PB – GAP block copolymers combine the advantages of HTPB and GAP, providing a compromise between mechanical properties and binder energetics in solid fuels.

Advantages:

– HTPB rubber segment improves the low temperature properties of GAP

– easier processing of the copolymer compared to GAP

– GAP segment in the copolymer increases the energy content of the binder

– improved mechanical properties

Plasticizers

Plasticizers are chemicals which are added to polymers and rubber in order to decrease viscosity, friction and improve mechanical properties with regard to plasticity. They are often applied to soften hard and brittle materials or facilitate processability of the material. Typically a plasticizer is a liquid of low volatility and high boiling point.

Plasticizers are important ingredients in solid propellant and plastic explosives, where play a dual role. Processability of polymer blend is facilitated, because of decrease in viscosity as well as mechanical properties are improved with regard to change in glass transition temperature and reduction in tensile strength. This aspects allow provide optimal properties suitable for storage, application and transportation of the final product.

Dioctyl Adipate
Dioctyl adipate is a plasticizer applied in many areas of industry. It is one of most common plasticizer used in production of solid propellants. Its advantageous properties allow to improve processability and pot life of propellants based on HTPB as well as assure good mechanical properties of the product. Dioctyl adipate is compatible with many synthetic rubbers and shows good thermal stability.
Molecular formula
Molecular weight	370.6 g/mol
CAS no	123-79-5
Appear	Oily, colourless liquid
Density	0.9268 g/cm³
Viscosity	13.7 cps
Boiling point	417°C
Vapor pressure	2.4 mmHg
Flash point	204.4°C
Refractive index	1.4474
Water solubility	no
Soluble in	alcohols, ether, acetone, most organic solvents

Isodecyl Pelargonate
Isodecyl Pelargonate is considered as one of the best plasticizer in HTPB based solid propellants. It exhibits remarkably low viscosity and is suitable for use at low temperatures. Application of isodecyl pelargonate improves significantly processability of HTPB blends.
Molecular formula
Molecular weight	298.5 g/mol
CAS no	109-32-0
Appear	Light yellow liquid
Density	0.862 g/cm³
Viscosity	6.2 cps
Boiling point	340°C
Vapor pressure	n/a
Flash point	172°C
Refractive index	1.4406
Water solubility	negligible

Diethyl Phtalate
Diethyl phthalate is a common plasticizer used in a wide range of applications including plastics, laquers, rubber coating agents and solid rocket propellants.
Molecular formula
Molecular weight	222.24 g/mol
CAS no	84-66-2
Appear	Colourless, oily liquid
Density	1.11 g/cm³
Viscosity	11 cps
Boiling point	295°C
Vapor pressure	0.002 mmHg (25°C)
Flash point	161.1°C
Refractive index	1.5000
Water solubility	1.08 g/L

Dibutyl Phtalate
Dibutyl phthalate is a plasticizer used in resins and polymers – especially PVC as well as in printing inks, adhesives, coatings, lubricants, antifoamers and solid propellants.
Molecular formula
Molecular weight	278 g/mol
CAS no	84-74-2
Appear	Colourless, oily liquid
Density	1,05 g/cm³
Viscosity	18,8 cP
Boiling point	340°C
Vapor pressure	0.00007 mmHg (20 °C)
Flash point	157°C
Refractive index	1,4900
Water solubility	13,5 mg/L

Dioctyl Sebacate
Dioctyl sebacate is a plasticizer, which shows excellent flexibility at low temperature, high plasticizing efficiency and resistance to extraction by water. It is used applied for softening PVC, polystyrene, synthetic rubbers as well as an ingredient of solid propellant blends, which lowers Tg of the product and improves mechanical properties at low temperature.
Molecular formula
Molecular weight	427 g/mol
CAS no	122-62-3
Appear	Colourless, oily liquid
Density	0,9 g/cm³
Viscosity	23 cP
Boiling point	256°C
Vapor pressure	0.000024 Pa at 37 °C
Flash point	210°C
Refractive index	1,4400
Water solubility	none