EBB 220/3 POLYMER ADDITIVES

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EBB 220/3POLYMER ADDITIVES
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Introduction

• Most of polymers need to add with specific
  ingredients to obtain desirable properties.
• Additives were used
• To improved or modify the mechanical, chemical,
  and physical properties
• To prevent degradation (both during fabrication
  and in service)
• To reduce materials costs
• To improve the processability
• Each of the additives in formulation has specific
  functions either during processing or end
  products applications
• Typical additives include
• filler materials,
• Plasticizer
• stabilizers,
• colorants
• flame retardants.

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Fillers

• Fillers normally add in polymeric materials for
  economical or technical
• Filler materials are most often added to polymers
  to improve tensile and compression strengths,
  abrasion resistance, toughness, dimensional and
  thermal stability and other properties.

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Fillers

• Materials used as particulate fillers ? include
  wood flour (finely powdered sawdust), silica
  flour and sand, glass, clay, talc, limestone, and
  even some synthetic polymers.
• Particle sizes range all the way from 10 nm to
  macroscopic dimensions
• Because these inexpensive materials replace some
  volume of the more expensive polymer, the cost of
  the final product is reduced.

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Plasticizers

• Can be in liquid, half solid or solid form.
• It must be compatible with the polymeric
  materials and other compounding ingredients ?
  incompatibility will results in poor processing
  properties.
• Plasticizer were used for
• extender (large amount gt20 pphr)? to make the
  end products cheaper
• Processing aid (small amount 2-5 pphr)? to make
  the processing easier
• Modifier ? to modifies some polymeric properties.

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• The aid of additives called plasticizers can
• improved the flexibility, ductility, and
  toughness
• produces reductions in hardness and stiffness
• lowers the glass transition temperature ? at
  ambient conditions the polymers may be used in
  applications requiring some degree of flexibility
  and ductility.
• These applications include thin sheets or films,
  tubing, raincoats, and curtains.

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Stabilizers

• Some polymeric materials under normal
  environmental conditions ?are subject rapid
  deterioration in mechanical properties.
• Most often this deterioration is a result of
  exposure to light ? in particular ultraviolet
  radiation and oxidation
• Ultraviolet radiation ?
• causes a severance of some of the covalent bonds
  along the molecular chain
• also result in some crosslinking.
• Oxidation deterioration is a consequence of the
  chemical interaction between oxygen atoms and the
  polymer molecules.
• Additives that counteract these deteriorative
  processes are called stabilizers.

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Colorants

• Colorants impart a specific color to a polymer
• They may be added in the form of
• dyes
• The molecules in a dye actually dissolve and
  become part of the molecular structure of the
  polymer.
• pigments.
• Pigments are filler materials that do not
  dissolve ? but remain as a separate phase
• have a small particle size, are transparent, and
  have a refractive index near to that of the
  parent polymer.
• Others may impart opacity as well as color to the
  polymer.

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Flame retardants

• The flammability of polymeric materials is a
  major concern, especially in the manufacture of
  textiles and children's toys.
• Most polymers are flammable in their pure form ?
  exceptions include those containing significant
  contents of chlorine and/or fluorine such as
  polyvinyl chloride (PVC) and polytetrafluoroethyle
  ne (PTFE).
• The flammability resistance of the remaining
  combustible polymers enhanced by additives called
  flame retardants.
• These retardants may function by
• interfering with the combustion process through
  the gas phase, or
• by initiating a chemical reaction that causes a
  cooling of the combustion region and a
  termination of burning.

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Special purpose additives
Additives Function
Blowing agents Gas generating chemicals that are necessary for manufacturing sponge or micro porous products
Odorants Strongly scented substances added in small amounts that are capable of imparting a pleasant scent
Antistatic agents Added to reduce the accumulated of dust or dirt on surface and also to minimize possibility of sparking resulting from the discharge of accumulated static electricity
Retarders Substances that used to reduce the tendency of rubber mix to scorch ? avoid premature vulcanization during processing
Antioxidants Protects products from oxidation of heat
Antiflex cracking Agents that retard cracking caused by cyclic deformations
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Example of the exams question

• What is the function of additives in polymeric
  materials?
• Discuss the used of fillers as one of polymer
  compounding ingredients.

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EBB 220/3MISCELLANEOUS APPLICATIONS
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Coating

• Coating are frequently applied to the surface of
  materials to serve one or more of the following
  function
• to protect the item from the environment that may
  produce corrosive or deteriorative reactions
• to improve the item's appearance
• to provide electrical insulation.

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• Many of the ingredients in coating materials are
  polymers ? with majority are organic in origin
• These organic coatings fall into several
  different classifications
• paint,
• varnish,
• enamel,
• lacquer, and
• shellac

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Adhesives

• An adhesive ? substance used to join together the
  surfaces of two solid material (termed
  "adherends") to produce a joint with a high shear
  strength
• Adhesives may come from either natural or
  synthetic sources.
• Some modern adhesives ?are extremely strong, and
  becoming increasingly important in modern
  construction and industry

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• Polymeric materials that fall within the
  classifications of thermoplastics, them setting
  resins, elastomeric compounds, and natural
  adhesives (animal glue, cast starch, and resin)
  may serve adhesive functions.
• Polymer adhesives may be used to join a large
  variety of material combinations metal-metal,
  metal-plastic, metal-ceramic, and so on.
• The primary drawback is the service temperature
  limitation.
• Organic polymers maintain their mechanical
  integrity only at relatively low temperatures,
  and strength decreases rapidly with increasing
  temperature.

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Some categories of adhesives

• Natural adhesives
• Adhesives based on vegetable (natural resin),
  food (animal hide and skin), and mineral sources
  (inorganic materials).
• Synthetic adhesives
• Adhesives based on elastomers, thermoplastic, and
  thermosetting adhesives.
• Drying adhesives
• These adhesives are a mixture of ingredients ?
  polymer dissolved in a solvent e.g. glues and
  rubber cements
• As the solvent evaporates ? the adhesive hardens
  and they will adhere to different materials to
  greater or lesser degrees.
• These adhesives are typically weak and are used
  for household applications. Some intended for
  small children are now made non-toxic.
• Hot adhesives (thermoplastic adhesives)
• Also known as "hot melt" adhesives
• they are applied hot and simply allowed to harden
  as they cool.
• These adhesives have become popular for crafts
  because of their ease of use and the wide range
  of common materials to which they can adhere.

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Adhesives failure

• Adhesives may fail in one of two ways
• Adhesive failure is the failure of the adhesive
  to stick or bond with the material to be adhered
  (also known as the substrate or adherend).
• Cohesive failure is structural failure of the
  adhesive. Adhesive remains on both substrate
  surfaces, but the two items separate.
• Two substrates can also separate through
  structural failure of one of the substrates ?
• this is not a failure of the adhesive. In this
  case the adhesive remains intact and is still
  bonded to one substrate and the remnants of the
  other.
• For example,
• when one removes a price label, adhesive usually
  remains on the label and the surface ? this is
  cohesive failure.
• If, however, a layer of paper remains stuck to
  the surface ? the adhesive has not failed.
• when someone tries to pull apart oreo cookies
  with the filling all on one side. The goal is an
  adhesive failure, rather than a cohesive failure.

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Films

• Polymeric materials have found widespread use the
  form of thin films.
• Films having thicknesses between 0.001-0.0005 in
  (0.025 -0.125 mm)
• Used extensively as
• bags for packaging food products and other
  merchandise,
• as textile products, and a host of other uses.
• Important characteristics of the materials
  produced and used as films include
• Low density,
• high degree of flexibility,
• high tensile and tear strengths,
• resistance attack by moisture and other
  chemicals,
• low permeability to some gases, especially water
  vapor.

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• Some of the polymers that meet these criteria and
  are manufactured in film form are
• polyethylene,
• polypropylene,
• cellophane, and
• cellulose etate.
• There are several forming methods
• simply extruded through a thin die slit ?followed
  by a rolling operation that serves to reduce
  thickness and improve strength.
• Blown moulding?
• continuous tubing is extruded through an annular
  die and maintaining a controlled positive gas
  pressure inside the tube,
• wall thickness may be continuously reduced( to
  produce a thin cylindrical film, which may be cut
  and laid flat.
• Some of the newer films ? produce using co
  extrusion that is, multi layers of more than one
  polymer type are extruded simultaneously.

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Foams

• Very porous plastic materials ? produced in a
  process called foaming
• Both thermoplastic and thermosetting materials
  may be foamed by ? including in the batch a
  blowing agent
• upon heating ?decomposes with the liberation of a
  gas.
• gas bubbles are generated throughout the
  now-fluid mass ?remain as pores up cooling and
  give rise to a sponge-like structure.
• The same effect is produced bubbling an inert gas
  through a material while it is in a molten state.
  

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• Some of commonly foamed polymers are
• polyurethane,
• rubber,
• polystyrene, and
• polyvinyl chloride.
• Foams are commonly used as
• cushions in automobiles and furniture
• in packaging and
• thermal insulation.

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Example of the exams question

• Discuss two of the various applications of
  polymeric materials.
• What are the polymer characteristic to produced a
  film?