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Hot melt extrusion thesis proposal

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The largest potential in the pharmaceutical industry resides with the processing of active or excipient materials to produce products such as:

thermal binders/ sustained release tablets,

medical grade film products/ transdermal drug delivery systems,

catheter tubing, granule preparation / immediate release dosage forms,

and hot melt mixed solid dosage forms.

Operational principles of HME and configurations:

Hot-melt extrusion is the process of pumping raw materials with a rotating screw under raised temperature through a die to a product of required shape. Hot-melt extrusion equipment consists of an extruder, auxiliary equipment for the extruder, downstream processing equipment, and other monitoring tools used for performance and product quality evaluation.

Hot melt extrusion thesis proposal rotating screw

The feed hopper, barrel, screw, die, screw driving motor and heating and cooling system are individual components within extruder. Most commercial extruders have a specific design to facilitate changing screws. The design of the screw has a significant impact on the process and can be selected to meet particular requirements such as high or low shear. (2)

The screw further divided into feeding, melting or compression and metering. The materials are transferred from the hopper to the barrel. Most of screw is made from stainless steel to avoid friction and chemical reaction. For easiest mass flow the channel depth is normally wider. The polymer is typically started to melt in the compression zone. The die is attached at the end of the barrel. Several types of downstream equipment are necessary to further process the extrudates into its desired form.

The primary function of the subsequent compression zone is to melt, homogenize and compress the extrudates so that it reaches the metering zone in a form suitable for extrusion.

The final section, the metering zone stabilizes the pulsating flow of the matrix, thus ensuring the extruded product has a uniform thickness. Constant screw flight depth and pitch helps maintain continuous high pressure to ensure a uniform delivery rate of molten material through the extrusion die and, hence, a uniform product.

Simple single screw arrangements consist of only a single rotating screw inside a stationary extruder barrel, whereas more advanced machines involve twin-screw systems which are either rotating in same or opposite direction.

Hot melt extrusion thesis proposal no longer wish to

Furthermore the two screw may be either intermeshing or non-intermeshing. It is common for the extrusion screw to be characterized by the length/diameter (L/D) ratio, which typically ranges from 20 to 40:1.

Single screw system doesn’t have enough mixing capacity compare to twin screw arrangement. Therefore this is not preferred for pharmaceutical industry. Twin screw extruders have more versatility, a more stable melting process and great output.

[Diagram of extruder screw from reference 4]

[Component parts of a single-screw extruder adapted from reference number: 3]

During the hot-melt extrusion process, different zones of the barrel are preset to specific temperature before the extrusion process. A mixture of polymers and processing material is then added into the barrel via hopper by rotating screw. Temperatures are controlled and monitored by electrical heating band and thermocouples respectively. The shearing effect of rotating screw gives effect as heating of material inside the barrel. The molten mass is eventually pumped through the die, which is attached to the end of the barrel. The extruders are then subject to further processing by auxiliary downstream devices.

Polymer and plasticizer used in process:


Always on Time
Marked to Standard

Hot-melt extruded dosage forms are mixtures of pharmaceutical ingredient and functional excipient. The selection of polymer for hot-melt extrusion process mainly depends on drug-polymer miscibility, polymer stability and function of final dosage form. A variety of carrier systems have been studied or used in hot-melt extrusion dosage forms. The properties of polymer can affect formulation, design and control of release of active compound as well.

Examples of pharmaceutically approved polymeric material include vinyl polymers (polyvinyl pyrolidoline, PVP-vinyl acetate), plyethylene oxide, Eudragit®, PEglycol and cellulose derivatives. (8)

Starch and starch derivatives have been applied along with low molecular weight excipients like sugars and sugar alcohols and waxes.(6 and 7)

A recent development is the use of surfactant to improve the release profile of solid dispersions. (7) Water soluble polymers have included hydroxypropyl cellulose, polyethylene oxide, poly(vinyl pyrrolidone) in which the drug is released by a diffusion and erosion mechanism.(4)

Plasticizers are typically low molecular weight compound capable of softening polymers to make them more flexible. Plasticizers are used in hot melt extrusion to improve the processing conditions during the manufacturing of the final product or its properties. Plasticizers can decrease the glass transition temperature and melt viscosity of a polymer by increasing the free volume between polymer chains. Plasticizers used for the preparation of pharmaceutical dosage forms must have good efficiency, stability, polymer – plasticizer compatibility and permanence. Triacetin. citrate esters, and low molecular weight polyethylene glycols have been investigated as plasticizers in hot-melt extruded systems. Additionally, several drug substances have been reported to function as plasticizers in hot-melt extruded dosage forms. (4)

Repka and McGinity (4) demonstrated that the amount of plasticizer remaining in hot-melt extruded films over time was a function of the plasticizer type and storage conditions. Plasticizers may also improve the physical-mechanical properties of hot-melt extruded dosage forms. In transdermal films, the addition of a plasticizer to the polymer matrix can improve the film’s flexibility (4). Plasticizers often influence the product’s tensile strength and elastic modulus.


Enhancement of the dissolution rate and bioavailability of a drug

Controlling or modifying drug release

Stabilizing the API

Parenteral depots and topical delivery system

Absence of solvents and water during processing

Economical process with less production time, and continues operation

No requirement on API compressibility of API and simple procedure

Wide range of performance dosage form

Good stability at different pH and moisture levels

Uniform dispersion of fine particle occurs.


High energy input due to shear forces and temperature

Design of screw and extruder dies have significant impact on the degradation of drugs and excipient

Flow properties of polymer are essential to processing

Cannot be applied to heat sensitive material

Limited choice of polymer.

Application in general:

Hot melt extrusion is mostly used in the plastic and rubber industries. Pipes, hoses, wires, tiles, plastic and rubber sheeting are made from extrusion process. Plastics that are commonly processed by extrusion include acrylics (polymethacrylates, polyacrylates) and copolymers of acronitrile, cellulosics (cellulose acetate, propionate, and acetate butyrate), polyethylene (low and high density), polypropylene, polystyrene, vinyl plastics, polycarbonates, and nylons. The process often is referred to different required shape by the die for example as in film extrusion, blow molding, or injection molding. In film extrusion, the polymer melt is extruded through rolls which make fine sheet of material.

In the food industry extrusion has been used since 1930 for pasta production. A widely used versatile technique combines cooking and extrusion in a so-called extrusion cooker.(9)

In the animal feed industry, extrusion is most commonly applied as a means of producing pelletized feeds. (10)

Application in pharmaceutical industries:

HME is considered to be an efficient technique in developing solid molecular dispersions and has been demonstrated to provide sustained, modified and targeted drug delivery resulting in improved bioavailability with specific required shape and size. Hot Melt extrusion process is currently applied in the pharmaceutical field for the manufacture of a variety of dosage forms and formulations such as granules, pellets, tablets, suppositories, implants, stents, transdermal systems and ophthalmic inserts, as well as other routes of administration.(11)

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In pharmaceutical industry the melt extrusion has been used for various purposes, such as:

a) Masking the bitter taste of an active drug.

b) Formation of polymer-drug solutions/dispersions:

Increased drug solubility

Increased drug dissolution rate

c) Formulation of controlled release dosage forms (including implants).

Melt extrusion may be applied to disperse drugs in a given matrix down to the molecular level, e.g. to form a true solution. It is the convenience of the technology that gives new hope to the glass or solid solution approach as a delivery system for poorly soluble drugs. The use of melts in order to obtain solid molecular dispersions, e.g. glass or solid solutions, is well known to the expert and the essential advantage of a melt process in this domain is its solvent-free formation of such dispersions.(3)

Commercial formulation:

SOLIQS, a pharmaceutical company has developed a proprietary MELTREX® formulation and redeveloped a protease inhibitor combination product, KALETRA®,for the treatment of human immunodeficiency virus. Kaletra formulation show significant advantage to the previous soft gel capsule formulation.(15)

SOLIQS has also developed sustained release formulation of verapamil and ibuprofen fast dissolving formulation was the first directly shaped HME product on market.

PHARMAFORM, a pharmaceutical company developed PADTTM technology to deter and prevent drug abuse.

Hot melt extraction process is capable for the development of controlled release formulations.

Rippie and Johnson prepared pellets containing cellulose acetate phthalate using a rudimentary ram extruder in 1969 to study the dissolution rates based upon pellet geometry (18). Follonier and coworkers in 1994 investigated the possibility of using hot-melt extrusion technology to produce sustained-release diltiazem pellets (17).

In 1996 and 1997, Miyagawa, Sato, and coworkers prepared controlled release matrices containing diclofenac as a model drug by hot melt extrusion (4).

Koleng and McGinity utilized hot-melt extrusion technology for the preparation of rapid release granules.

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