Metin Atmaca 030080007 8th week definitions part 2

3. Biocides (Polymer Additives):

Previous Definition:

The biggest customers for biocidesare outside the plastic industry, which actually accounts for only a very small fraction of all the biocides used. According to the Biocide Information Service, the most important single antimocrobial application in plastics is PVC flooring which uses more than a third of all the biocides incorporated in plastics products. The second most important application is the protection of hygienic surfaces such as worktops. Smaller amounts are used in PVC pool liners, floorcoverings, artificial leather, tarpaulins and tents. Other outlets include rubbish sacks, food packaging and footwear. In japan, antimicrobials are used in telephone hand sets (one of the commonest sites of infection) and in pens. There are growing markets for biocides in medical devices and wood plastics composites.

The original purpose of antimicrobial additives in plastics was to protect the materials, not the users. This applied especially to flexible PVC which needs protection in moist atmospheres from mildew, moulds and funghi. The situation has changed considerably in the last five years, with more use being made of antimicrobial products designed to promote a hygienic image for the product, to protect surfaces and to reassure human users of bathroom, medical and food related products.

(Pritchard G., Plastic additives, 2005, p. 85)

New Definition (Better):

Biocides, also known as antimicrobials, preservatives, fungicides, mildewcides, or bactericides, are used to impart protection to plastic parts against mold, mildew, fungi, and bacterial growth. Without biocides certain plastics in moist environments may experience development of spores on the surface of the material, which could cause allergic reactions, odors, staining, and embrittlement. Such degradation could actually cause the part to fail prematurely.

It should be noted that biocides are intended only to protect the plastic part. They are not intended to protect humans from microbial contamination. There is often confusion regarding claims made concerning biocides. In the United States, all biocides are also considered pesticides and must be registered with the EPA.

Biocides are usually dispersed in plasticizer, oils, or other low-molecular-weight carriers that can migrate to the surface of the part. The rate of migration relative to the rate of leaching of the biocide from the surface is an important parameter in formulating with biocides. This mobility results in the gradual leaching of the additive. If significant leaching occurs, the product will be left unprotected after time. The proper balance between the rates of migration and leaching determines the durability of protection.

Biocides are available as an active ingredient or as a formulated product. They can be powders, liquids, or pellets. Concentrations in the final plastic part vary from 1 percent down to 0.04 percent depending on the activity of the biocide. Biocides are generally formulated with a carrier (usually a plasticizer) into concentrations of 2–10 percent of the active ingredient. The plasticizer, commonly epoxidized soybean oil or diisodecyl phthalate, aids in the migration of the biocide to the surface of the part.Biocides are commonly used in flexible polyvinyl chloride (PVC) parts that are intended for moist, warm environments. Applications include PVC flooring, garden hoses, pool liners, shower curtains, etc. They are also used with polymeric foams andother resins.

Commercially available biocides include OBPA (10,10-oxybisphenoloxarsine) from Akzo Nobel, Witco, and Morton; zinc-omadine (zinc 2-pyridinethanol-1- oxide) from Olin; and Triclosan (trichlorophenoloxyphenol) from Allied Resinous Products, Ciba Specialty, and Microban. Major suppliers also include Ferro, Huels, Microban, Ciba, and Rohm and Haas.

(Harper, C.A., Petrie, E.M., Plastic Materials and Processes, p. 55)

4. Antioxidants (Additive Material)

Previous Definition:


The combined action of oxygen and heat during the life cycle of polymers(manufacture, processing, storage and end use) causes thermooxidation of materials. This phenomena generate a change in molecular weight that lead to modificiations of physical and mechanical characteristics such as increase or decrease of melt flow, yellowing or dislocation, loss of gloss or transparency, chalking and superficial micro-cracks. After  the superficial changes in the degradation continues to greater extent thus decreasing the mechanical properties ( elongation at break, tensile strength, impact strength, flexural modulus). With ongoing aging the characteristics of the plastic artice are so modified that it loses its usefulness. The thermal oxidation reaction can be inhibited as follows;

-          -Using a primary antioxidant that inteferes with the chain propagation step

-          -Through a radical termination reaction

-          -Using a secondary antioxidant taht decomposes the hydroperoxides

-          -Primary antioxidants belong to the hindered phenols chemical family, called also “Radical Scavengers”. Secondary antioxidants belong to Phosphite/ Phhosphonite and Trioethers chemical family. The combination of both Antioxidant classes allows to achieve a synergistic effect.

(Ernest W. Flick, Plastic Additives, p. 62)

New Definition (Better):

Antioxidants are used in a variety of resins to prevent oxidative degradation. Degradation is initiated by the action of highly reactive free radicals caused by heat, radiation, mechanical shear, or metallic impurities. Plastics degradation starts with the initiation of free radicals on exposure to heat, UV radiation, and mechanical shear or in the presence of reactive impurities such as catalyst residues. The radicals thus initiated have a high affinity for reacting with oxygen to form unstable peroxy radicals. These radicals, in turn, attract neighboring labile hydrogens to produce unstable hydroperoxides plus additional free radicals that keep the process going. This leads to degradation of the polymer. Only when a nonradical inert product is formed will the cycle be terminated. In preventing this type of degradation, the antioxidants function by intercepting the radicals or by preventing radical initiation during the plastic’s life cycle.

The function of an antioxidant is to prevent the propagation of oxidation. Because many plastics are susceptible to oxidative degradation, the role of antioxidants in slowing down the process and imparting longer life to many products has taken on added importance. Depending on the aging environment, most plastics can benefit from antioxidants. Plastics especially susceptible to oxidation such as polypropylene, polyethylene, ABS, and polystyrene often include antioxidants in their formulations.

Antioxidants can be divided into two basic classifications: primary and secondary antioxidants. Primary antioxidants interrupt oxidation degradation by tying up the free radicals. Secondary antioxidants destroy the unstable hydroperoxides that function as sources of free radicals during oxidative degradation.

The two major groups among the primary antioxidants are hindered phenolics and aromatic amines. The most widely used antioxidants in plastics are phenolics. The products generally resist staining or discoloration. However, they may form quinoid (colored) structures on oxidation. Phenolic antioxidants include simple phenolics, bisphenolics, polyphenolics, and thiobisphenolics. Hindered phenolics, such as butylated hydroxytoluene (BHT), high-molecular-weight phenolics, and thiobisphenolics, are the most popular of the primary antioxidants. Aromatic amines, normally arylamines, may be more effective than phenolics, but most are staining and discoloring and lack FDA approval for use in contact with food. Amines are commonly used in the rubber industry but also find minor uses in plastics such as black wire and cable formulations and in polyurethane polyols.

Secondary antioxidants are used in conjunction with primary antioxidants to provide added stability to the polymer. Typical compounds contain sulfur or phosphorus. The more popular secondary antioxidants are thioesters (thiodipropionic acid derivatives and polythiodipropionates) and organophosphites.

(Harper, C.A., Petrie, E.M., Plastic Materials and Processes, p. 38)

5. Colorants (Polymer Additives)

Previous Definition:

An advantage of many polymers over metal or ceramics is that the material itself can be obtained in most any color. This eliminates the need for secondary coating operations. Colorants for polymers are of two types: pigments and dies. Pigments are finely powdered materials that are insoluble in and must be uniformly distributed throughout the polymer in very low concentrations, usually less than %1. They often add opacity as well as color to the plastic. Dies are chemicals, usually supplied in liquid form that is generally soluble in the polymer. They are normally used to color transparent plastics such as styrene and acrylics. (Mikell P. Groover; Fundamentals of Modern Manufacturing Materials, Processes, and Systems 3rd Edition; pg.156)

New Definition (Better):

Colorants are added to plastic formulations to produce color in the polymeric part. They are separated into pigments and dyes. Pigments are insoluble in the polymer, whereas dyes are soluble in the polymer. The particular color desired and the type of polymer will affect the selection of the colorants.

Colorants come in several forms including liquids and dry concentrates. Color concentrates are typically used at a level of 3–4 percent. They are available in several forms including pellet, dice, chip, granular, or strand. The selection of the proper colorant form involves many factors: volume requirements, handling provisions, metering equipment, and labor and inventorying costs when comparing overall costs.

(Harper, C.A., Petrie, E.M., Plastic Materials and Processes, p. 101)