NATURAL PRODUCT-BASED POLYMER

ADDITIVES

Importance of Polymer Additives (1) Polymer/Plastic additives represent a

broad range of chemicals used by manufacturers, compounders, and fabricators to improve the properties, processing, and performance of polymers.

Plastics additives have grown with the overall industry and currently represent over $16 billion in global sales.

Some Plastic additives are complex organic molecules (antioxidants and light stabilizers for example) designed to achieve dramatic results at very low loadings.

Importance of Polymer Additives (2) Few commodity materials (talc and glyceryl

monostearate) which also can impart significant property improvements.

Many varied chemical materials can, and frequently do, compete in the same function.

Same material type may perform more than one function in a host plastic. For example surfactant materials based on fatty acid could impart lubricant, antistatic, mold release, and/or slip properties to a plastic matrix.

Plastic additives are generally classified by their function rather than chemistry.

Type of Polymer Additives Antiblock and Slip

Agents Antioxidants Antistatic Agents Biocides Chemical Blowing

Agents Coupling Agents

Flame Retardants Heat and Light

Stabiliser Impact Modifiers Lubricants Nucleating Agents Organic Peroxides Plastisisers

Antiblocking Agents:function by roughening thesurface of film to give a spacing effect

Antioxidants:are used in a variety of resins to prevent oxidative degradation

The function of an antioxidant is to prevent the propagation steps of oxidation

Primary antioxidants, usually sterically hindered phenols, function by donating their reactive hydrogen to the peroxy free radical so that the propagation of subsequent free radicals does not occur. The antioxidant free radical is rendered stable by electron delocalization.

Secondary antioxidants retard oxidation by preventing the proliferation of alkoxy and hydroxy radicals by decomposing hydroperoxides to yield nonreactive products. These materials are typically used in synergistic combination with primary antioxidants.

Antistatic Agent or Antistat:is to prevent the buildup of static electrical charge resulting from the transfer of electrons to the surface

When the unprotected plastic is brought into contact with another material, loosely bound electrons pass across the interface, and when these materials are then separated, one surface has an excess charge, while the other has a deficiency of electrons

In most plastics the excess charge will linger or discharge, causing the following problems:

Fire and explosion hazardsPoor mold releaseDamage to electrical componentsAttraction of dust

Antistats function to either dissipate or promote the decay of static electricity. Secondary benefits of antistat incorporation into polymer systems include improved processability and mold release, as well as better internal and external lubrication

Therefore, in certain applications, antistatic agents can also function as lubricants, slip agents, and mold release agents

Biocides:are additives that impart protection against mold, mildew, fungi, and bacterial growth to materials

Biocides, also referred to as antimicrobials, preservatives, fungicides, mildewcides, or bactericides, include several types of materials that differ in toxicity

All biocides are considered pesticides and must be registered for specific applications with an Environmental Protection Agency

The effectiveness of a biocide depends on its ability to migrate to the surface of the product where microbial attack first occurs

Most biocides are carried in plasticizers, commonly epoxidized soybean oil or diisodecyl phthalate, which are highly mobile and migrate throughout the end product

Mobility of biocides results in the gradual leaching of the additive, and if significant leaching occurs, the product will be left unprotected, and the biocides may contaminate the media

The proper balance between the rates of migration and leaching determines the durability of protection

Physical Blowing Agents: are volatile liquids or compressed gases that change state during processing to form a cellular structure within the plastic matrix

The most common gases used are carbon dioxide, nitrogen, and air. The liquid blowing agents are typically solvents with low boiling points, primarily aliphatic hydrocarbons and their chloro- and fluoro- analogs

The blowing agents should be soluble in the polymer under reasonably achievable conditions but excessive solubility is not desirable

The permeability of the gas within the polymer is also significant, as is the volume of gas released per unit weight of agent

This latter measure is called the blowing agent efficiency, and is an important yardstick for all types of materials

Effective blowing agents should yield at least150 to 200 cm3 of gas (measured at standard temperature and pressure) per gram of agent

Coupling Agents:are additives used in reinforced and filled plastic composites to enhance the plastic–filler-reinforcement interface

In general, there is little affinity between inorganic materials used as reinforcements and fillers and the organic matrices in which they are blended

With silicate reinforcements (glass fiber or wollastonite), silane coupling agents act by changing the interface between the dissimilar phases

By chemically reacting with the resin and the filler or reinforcement components, coupling agents form strong and durable composites

Coupling agents significantly improve mechanical and electrical properties for a wide variety of resins, fillers, and reinforcements

In addition, they act to lower composite cost by achieving higher mineral loading

Silanes and titanates, make up the major coupling agent marketTable 4.8 lists four different silane chemistries and their related composite systems

Flame Retardants, work by minimizing at least one of the requirements for a fire to exist, namely, fuel, heat energy, and oxygen, they also may be classified in another way as follows:

Char formers. Usually phosphorus compounds, which remove the carbon fuel source and provide an insulating layer against the fire’s heat

Heat absorbers. Usually metal hydrates such as aluminum trihydrate (ATH) or magnesium hydroxide, which remove heat by using it to evaporate water in their structure

Flame quenchers. Usually bromine or chlorine-based halogen systems which interfere with the reactions in a flame

Synergists. Usually antimony compounds which enhance performance of the flame quencher

Reactive flame retardants, chemically bind with the host resin

Flame Retardants reduce the ease of ignition smoke generation and rate of burn of plastics, at loading levels from a few percent to more than 60%

Flame retardants are in a unique position among plastics additives in that they are both created and yet are threatened by regulations, which accounts for 85 to 90% of the global sales of flame retardants

The huge $2.3 billion industry was created over the years by various industry, in The USA, which aimed to protect people from fire and smoke situations

Without these regulations, the plastics industry,, wouldn’t use these products because they are expensive and lower the physical properties of the plastics in which they are employed

Heat Stabilisers are used to prevent the thermal degradation of resins during periods of exposure to elevated temperatures

Almost all heat stabilizers are used to stabilize PVC, PVDC, vinyl chloride copolymers, and PVC blends, during processing as well as during the useful life of the finished products

There are three major types of primary heat stabilizers, which include:

Mixed metal salt blendsOrganotin compoundsLead compounds

Primary heat stabilizers function both by retarding liberation of HCl from the chlorinated vinyl resins and by reacting with the liberated HCl to delay progressive degradation

Secondary heat stabilizers or costabilizers are used to scavenge liberated HCl from the chlorinated resins or to react with the metallic chloride by-products of the primary mixed metal stabilizers

Impact Modifiers are used in a wide variety of thermoplastic resins to absorb the energy generated by impact and dissipate it in a nondestructive fashion

Light Stabilisers are used to protect plastics, particularly polyolefins, from discoloration, embrittlement, and eventual degradation by UV light

Three major classes of light stabilizers are:

UV absorbers,Excited state quenchers, and Free-radical terminators

Each class is named for the mechanism by which it prevents degradation

The major types included in each light stabilizer class may be categorized by their chemistries, as shown in Table 4.17

Lubricants represent a broad class of materials that are used to improve the flow characteristics of plastics during processing

Lubricants can act as melt promoters, antiblock, antitack, and antistatic agents as well as color and impact improvers

They can be used in conjunction with metal release agents and heat stabilizers

Lubricants are widely used in packaging film to prevent sticking to the metal processing equipment

External lubricants do not interact with the polymer but function at the surface of the molten polymer between the polymer and the surface of the processing equipment and are generally incompatible with the polymer itself. These lubricants function by coating the process equipment and reducing friction at the point of interface

Internal lubricants are usually chemically compatible with the polymer and act by reducing friction between polymer molecules. They reduce van der Waals forces, leading to lower melt viscosity and lowering energy input needed for processing

Nucleating Agents are used in polymer systems to increase the rate of crystallization

Nucleating agents can shorten cycle time by reducing set-up time in the mold, but care must be taken to ensure that shrinkage and impact properties are not negatively affected

With some difficult-to-crystallize thermoplastics, such as partially aromatic polyamides or PET, nucleants are needed to obtain useful parts with reasonable cycle times and mold temperatures

The optical benefits of nucleating agents are increased clarity and improved gloss, because of an increase in the number of fine crystals

When crystals are smaller than the wavelength of visible light, the light is scattered at smaller angles, decreasing the hazy effect seen when nucleating agents are not used

When utilized to improve transparency in materials such as PP, these materials are referred to as clarifiers or clarifying agents. An example of how clarifiers work is depicted in Fig. 4.1

Organic Peroxides serve as sources of free radicals in the preparation of a variety of resins for plastics, elastomers, and coatings

Their usage in plastics processing can be divided into four functions:

Polymerization of thermoplastic resinsCuring for unsaturated polyester thermoset resinsCross-linking of polyethylene and various elastomersVisbreaking (rheology modification) of polypropylene

The peroxide group (—O—O—) contained in all organic peroxides is highly unstable, which eventually leads to homolytic cleavage between the two oxygen molecules, the peroxide decomposes and two free radicals are formed

The general formula for such compounds is R1—O—O—R2, whereby R1 and R2 either symbolize organic radicals or an organic radical and hydrogen atom

Organic Peroxides Initiators can be further classified by functional groups into seven major classes as follows:

Plasticizers are the largest volume additives in the plastic industry Plastisisers are largely used to make PVC and other resins

flexible and are generally regarded as commodity chemicals

The primary role of a plasticizer is to impart flexibility, softness, and extensibility to inherently rigid thermoplastic and thermoset resins

Secondary benefits of plasticizers include improved processability, greater impact resistance, and a depressed brittle point

Plasticizers can also function as vehicles for plastisols (liquid dispersions of resins which solidify upon heating) and as carriers for pigments and other additives

Some plasticizers offer the synergistic benefits of heat and light stabilization as well as flame retardancy

In some cases, it is difficult to discern if a particular polymer additive functions as a plasticizer, a lubricant, or a flame retardant

Plastisisers are categorised based on their chemical compounds, and total number of plasticizers available to formulators is substantial

Phthalate esters, the most commonly used plasticizers, are manufactured by reacting phthalic anhydride (PA) with 2 moles of alcohol (from 6 to 13 carbons) to produce the diester

Aliphatic esters, are generally diesters of adipic acid, sebacic and azelaic acids with usually either 2-EH or isononanol alcohols

Epoxy esters. Epoxidized soybean oil (ESO) is the most widely used epoxy plasticizer, also used as a secondary heat stabilizer, but have limited compatibility in PVC, and are used at low levels

Phosphate triesters. Phosphorous oxychloride can be reacted with various aliphatic and aromatic alcohols and phenols

Trimellitates are esters of trimellitic anhydride and characterized by low volatility, for examples: trioctyl trimellitate (TOTM) and triisononyl trimelliate (TINTM)

Polymer plasticizers of esters of diols with dibasic acids yields high molecular weight (1000 to 3000), and are used with phthalates to improved permanence and reduced volatility

Challenges on Utilisation of Polymer Additives (1)

Commercial additives are generally mineral oil-based, which some of them are revealed toxic and carcinogenic, as well as non-renewable and non-degradable in nature

They are still widely used even for various products directly related to foods and human contact consumer goods, i.e: crockeries, households, toys and children health, as well as medical appliances

Therefore, healthy and environment-friendly plastic additives, which are natural product-based and renewable, are not only economically feasible but also safer alternatives for the mineral-oil based additives.

In addition, low molecular weight additives may usually migrate or leach out from the polymer matrices and lost their substantivity during their utilisation

This is consequently not only causing contamination of the additives into the media, but also leaving the polymer matrices without additives to degrade to their low properties.

Challenges on Utilisation of Polymer Additives (2)

Problems of additive loss and contamination can be overcome by utilisation of higher molecular weight additives to reduce rate of their migration

Other alternatives to improve substantivity of the additives is to prepare their derivatives containing polymer reactive groups, so that can be chemically bound onto the polymer backbone.

Polymer-bound additives based on biodiesel plant glycerol residue are being prepared as plastisisers for thermoplastic matrices

The work is in collaboration between University of Sumatra Utara and Indonesian Oil Palm Research Institute in Medan, supported by The Indonesian Agricultural Research and Development Institute, and involving doctorate and master students of our Postgraduate School