Additive Types

There are several categories of additives such as stabilizers, processing aids, plasticizers
anti-statics, blowing agents, fillers, coupling agents, antibacterial additives, desiccants
and color changing additives. These additives are vital to the production of the many
types of polymers that are on the market today. They help to maximize the performance
.of the materials and to produce a product that fulfills production needs

Stabilizers

Antioxidants are a type of stabilizer that can protect a material during processing and
extend the material’s longevity. They are used to prevent degradation of polymers that
can result in loss of strength, flexibility, thermal stability, and color. Antioxidants
perform by eliminating oxidation during and after processing when materials are exposed

to an energy source

A second category of stabilizers are those that help materials withstand UV light
Ultraviolet radiation damages chemical bonds of polymeric materials; therefore addition
of UV stabilizers is critical to produce materials that will provide good performance even
when exposed to UV radiation over extended periods. These stabilizers function by
absorbing high energy UV radiation and then releasing it at lower energy level that is less
harmful to the polymer. For example Titanium dioxide has a high refractive index which
enhances long term stability and protects against material discoloration

A third category of stabilizers prevent thermal breakdown of materials and preserve aesthetic properties

These are known as heat stabilizers, which function by eliminating chemical decomposition during processing
The fourth category of stabilizer is flame retardants, which are formulated to
promote extinguishing of a polymer. Many polymers are flammable in their pure form
therefore addition of flame retardants can help protect materials and their contents
Flame retardants function by interfering with the combustion process or creating a new The additive is designed to
process easily and have no impact on the other physical properties of the material combustion reaction that generates less heat The additive is designed to process easily and have no impact on the other physical properties of the material

Processing Aids

Polymer processing aids are used to provide higher quality and better output and to
shorten cycle times. The two major types of processing aids are nucleating/clarifying
.agents and lubricants

Nucleating/clarifying agents

Nucleating/clarifying agents are chemical structures that increase the overall
crystallization rate of polymers. They can be used to increase stiffness, hardness, impact
properties, tensile strength, and to control the size and distribution of pores

The increased rate of crystallization result s in more crystals being produced in the
same amount of space; therefore, crystals that tend to be smaller. The smaller, tightly
packed crystals reflect less light so they have much higher clarity (Soroka, 2002). Higher
crystallization speed also helps a polymer solidify faster when cooling, which can lead to
.reduced machine cycle time and increased production

A commercial example of nucleating agents/clarifiers is the Milliad® additive
that was created by Milliken Chemical (Spartanburg, SC) for transparent polypropylene
packaging. This additive allows for faster processing and improved clarity, gloss, and
barrier properties. The ability to provide clarity for polypropylene packaging can be
much less expensive than use of a material such as polyethylene terephthalate that is
.normally used for products in need of high clarity

Lubricants

Lubricants are used to improve flow and processing properties. There are a variety of
types available with varying properties that can greatly improve mixing, extrusion, and
calendaring behavior of materials. An internal lubricant is a type of additive that acts by
modifying material viscosity. The trend today is to utilize value-added internal lubricants
that can also modify other properties. By achieving multiple goals lubricant additives can
.be more cost effective

Slip additives are a type of internal lubricant that creates better processability by
reducing the internal friction and tackiness of polymers. Slip additives are used to reduce
the surface friction of polymers. They are very common in the film industry because the
slip additive helps film layers slide over each other which can be very useful in high
.speed packaging processes

Anti-blocking additives are another type of internal lubricant that can improve
processability during production. Anti-blocking additives prevent film layers from
sticking together. There are many types of anti-blocking additives that can provide a
diverse offering of formulations. For instance, there are expensive synthetic silica
formations that give high clarity. Alternatively, calcium carbonate is used for simple
anti-blocking for when clarity is not important. When these two internal lubricants are
used in combination, anti-blocking reduces the effectiveness of the slip agent. When
these additives are used together this effect must be considered to determine the best
.formulation for the polymer mixture

Plasticizers

Plasticizers are additives that increase the plasticity or flexibility of a plastic material
The plasticizers soften the final product, thus increasing movement and durability
Plasticizers work by embedding themselves between the polymer chains and pushing
chains further apart. This result s in a more flexible plastic, but causes a loss of strength
and hardness. Plasticizers are most commonly used with polyvinyl chloride because
without assistance it is too rigid to be processed. Plasticizers can be helpful for
production, but they are potentially toxic and should not be used for food packaging
.applications for fear of migration into foods

Anti-statics

The choice of anti-static is crucial and is determined by a wide range of factors such as
polymer type, processing conditions and end application. Anti-static additives allow
polymeric materials to disperse static electricity charges. Static charges can attract dust
or interfere with production (Soroka, 2002). An additive can be fast acting to reduce dust
attraction and can be formulated to give long term effects in demanding applications
Combinations with anti-block and slip products are often used in the film industry to
.maximize cost effectiveness and high performance

Blowing Agents

Blowing agents are additives that decompose to form a gas that will expand a polymer’s
cellular structure. This is used to create foams and expandable materials that are light
and provide thermal and/or shock protection. A common example is expanded
polystyrene (EPS), which is used heavily in packaging applications. To do this
polystyrene is combined with a blowing agent in a mold and then heated so that the
blowing agent is activated and the polystyrene expands (Soroka, 2002). EPS has
developed a bad reputation because some foams use chlorofluorocarbons (CFCs) which
erode the ozone layer. EPS does not contain CFCs; instead it is created by using pentane
.gas as a blowing age

Fillers

Fillers are added to polymers mainly to reduces cost and improve the properties of the
material. Polymers use less expensive fillers to replace some of the volume of more
expensive materials. Fillers can improve processing, abrasion resistance, density control
dimensional and thermal stability, and optical effects. Common fillers are wood, silica
.glass, clay, and other polymers 

Coupling Agents

The primary purpose of coupling agents is to increase interactions between polymer and
filler. They create chemical links between molecules to improve bonding. When the
coupling agents bond to a polymer they can enhance the adhesion between the two
.materials

Since coupling agents promote bonding, they can be used to encourage materials
that are normally incompatible to bond together. This effect can be very useful for trying
.to create new polymer blends and for reusing old polymer material

Antibacterial Additives

Anti-bacterial additives are used to create a resistance to microorganisms so that
polymeric materials are protected from bacterial growth. The additives operate by
interfering with the metabolism of microorganisms to block enzyme systems. To be
effective the additive must be able to migrate to the surface of the material so that it can
.interact with the microorganisms

Desiccants

Desiccants can be coextruded in-between layers of resin for moisture control. This
process is accomplished by using a co-extrusion head on the molding machine to create a
multilayer wall in the package. For example TricorBraun (St. Louis, Missouri) has
developed a DryKeep™ blend made with Magnesium Sulfate and HDPE/LDPE to create
a blow molded resin. Benefits of having a desiccant in the layers of the packaging are
.that it can absorb moisture from inside or outside the bottle

Color changing additives

Color changing additives can be added to polymers to change with their environment
such as temperature changes or UV exposure. For example, there are coffee lids that
change color when hot so that consumers can identify when the product should be
handled with caution. The production process is the same except the plastic is imbedded
with thermochromic dye during manufacturing. The color changing technology is safe in
.food contact situations and is FDA compliant

Polymers can also change color when exposed to UV light. For example
suntan lotion bottles can act as a sensor that changes color in the sun so consumers know
.when to use the product

Other additives

There are various other additives that provide a kaleidoscope of additional properties
For example, degradation additives are used to encourage a polymeric material to break
down, which means the materials are less harmful to the environment. There are also
additives that modify barrier properties by using recent developments in nanotechnology
to adjust the gas transmission rate of films. Additionally, there are polymer additives that
are used to create aesthetic features to attract consumers. Additives that can make a
product more appealing to consumers are color pigments or dyes, gloss controllers
.antifogging agents, and optical brighteners

Equipment

There a few vital pieces of equipment and machinery which are essential for processing
additives. Volumetric or gravimetric feeders and blenders are the most important
equipment that handles and incorporates additives into polymer blends. Volumetric
devices measure volume that passes through a metering disk while gravimetric devices
measure and control the weight of additives dispensed over a given time period.
Gravimetric types are recommended for cases when two or more additives are being
dispensed at either the machine throat or in a blending system. The blending system can
be either a dosing or mixing unit, which divides the main component into different
streams of material so the streams can combine with additives at the feed inlet to produce

a homogenous mixture. Another important piece of equipment is level sensors because
.they can measure insufficient additive material in order to prevent unnecessary downtime