Some measures to control odour in plastic products

Many plastic finished products have an inherent odour that is quite objectionable. It has been a long drawn effort by polymer manufacturers, compounders and fabricators to reduce levels of offensive odours emitted by finished plastic products. This is typically accomplished by replacing unpleasant smelling additives with low-odor substitutes, minimizing levels of monomers in plastics, adding odour absorbers to plastics and using anti microbial agents to prevent formation of musty odours by bacteria and fungi. In the processing of recycled plastics, solvent extraction and degassing can help reduce lingering odours.
Many inherent materials found in plastics are responsible for objectionable odours. They include amines, phenols, mercaptans, peroxides, styrene, aldehydes, ketones, alcohols and some plasticizers and fire retardants. Organic solvents used in plastics processing can also give off strong chemical smells. First of all those additives that offer objectionable odour, should be replaced, if feasible, by those additives that offer no odour. For example, in PVC products, heat stabilizers like Lead or mixed metal containing barium and zinc can be easily replaced by octyl tin or zinc heat stabilizer. Traces of monomers can produce unpleasant odours in many polymers, particularly in PVC, polystyrene, polyvinyl acetate and acrylic esters. Selecting resins with a minimum of monomer residues can eliminate these odours.
Polymer formulations can be filled with small amounts of synthetic zeolites, such as molecular sieve powders based on metal aluminosilicates, to absorb unwanted odours within the materials. The additives do this by trapping the organic odour-producing molecules within their highly porous crystal structures. Molecular sieve absorbents have been successfully used in extruded polyolefin pipes, injection and extrusion blow-molded containers, barrier packaging materials, extrusion coatings and sealant polymers. Molecular sieve powders can also be incorporated into plastics as desiccants to remove the moisture that contributes to odours.
Antimicrobials are often added to plastics, not only to reduce odours, but also to retard surface growth, staining and embrittlement. The most common antimicrobials are 10,10'-oxybisphenoxarsine (OBPA), trichlorohydroxydiphenylether (Triclosan), n-octyl-isothiazolinone (OIT), 4,5-di-chloro-isothiazolinone (DCOIT), mercaptopyridine-n-oxide (pyrithione), and butyl-benzisothiazolinone (butyl-BIT). Organometallic compounds of tin and silver are also sometimes used as antimicrobials. They also help in reducing the odours.
Another way to rid plastics of unwanted smells is to expose them to external odor absorbing agents such as activated charcoal or high-surface-area silica. This may be done under a vacuum to speed up the process.
Rinsing plastics in specially formulated detergent solutions can also aid in odour removal. Typically these are aqueous, alkaline solutions containing surfactants, useful in eliminating odours from vinyl monomers, styrene, acrylates, acrylic monomers and unsaturated hydrocarbons.
The addition of pleasant-smelling fragrances to plastics does not eliminate odours, but it masks them, which is sufficient for many purposes. Commercial scents are available for such polymers as PE, PP and olefin thermoplastic elastomers. They are suitable for injection moulding, extrusion or blow moulding. Fragrances do not always last for the lifetime of the moulded article. Their longevity depends on the initial concentrations, volume to surface-area ratio, exposure to heat or humidity and whether the finished parts are packaged in air-tight barriers. Typical applications of fragrances include toys, household goods, cosmetic containers, consumer electronics, and lawn and garden equipment.
Odours are a constant problem with post-consumer plastics. Most plastics that are recycled, such as PE, PP, PS, PVC or PET, are subjected to a washing step with aqueous solutions to remove contaminants. But odours trapped inside the recycled resins may linger. Solvent extraction using organic solvents can help eliminate the compounds responsible for these odors. A recent development has been solvent extraction using supercritical carbon dioxide as the solvent. The technology, which has been demonstrated on HDPE and PET can remove odorous contaminants from plastic oil containers, pesticide containers and other post-consumer items. The advantage of the CO2 system is that it does not employ organic solvents, which present troublesome disposal problems.
The degassing units that are part of the extruders used to pelletize plastics recyclate are also effective in stripping away some of the more volatile compounds that produce unwanted odors.
Because odors are subjective phenomena, it is a challenge to develop a system for classifying and measuring them. The first step in identifying odours objectively is to use panels of human test subjects to detect and rate odours on the basis of how pleasant or unpleasant they are. Responses of these panels can then be co-related with measurements of volatiles in plastics made with standard instrumental analytical methods such as gas chromatography/mass spectroscopy (GC/MS). But these older instrumental systems require careful evaluation by experts to interpret correctly.
Newer plastics odour detection instruments, known as "electronic noses," rely on electronic gas sensor arrays and pattern recognition technology. To use them, technicians heat a sample to drive off the volatiles, which are conducted to the sensor arrays. The results are presented in a statistical pattern that is easily correlated with sampling results from human panelists. Depending on the desired level of detail, odours from the volatiles may be classified as pleasant, neutral or unpleasant, or reported as intensity and molecular concentrations.

Naptha - What is it?

Naphtha's price rise causes anxiety. It signals an inevitable increase in polymer prices. So what is naphtha? Is it a compound? Naphtha is a generic term applied to any one of a wide variety of volatile hydrocarbon mixtures. They are obtained from coal tar or more often from petroleum.

Petroleum naphtha or mineral naphtha is obtained from petroleum as a crude distillate that is lighter than kerosene and has a lower boiling point. It contains a mixture of methane-type hydrocarbons. The distillates with lower boiling points than petroleum naphtha are called ligroin.

Other forms of naphtha are crude naphtha, obtained from coal tar; shale naphtha, obtained from shale; and wood naphtha, obtained from wood.

Solvent naphtha, used for dissolving rubber, is a high-boiling-point fraction distilled from coal tar. Physical properties vary widely depending on the mixture. Initial boiling point may may be as low as 27°C and end points may reach as high as 260°C. Boiling ranges could be as narrow as 11°C or as high as 110°C. In the strictest sense of the term naphtha, not less than 10% of the material should distill below 175°C and not less than 95% should distill below 240°C. Strictly speaking refinery products like gasoline and kerosene are also naphthas.

Naphthas are primarily produced by fractional distillation. Extractive distillation is used when certain high quality naphthas are desired. Acid, clay treating removes sulphur compounds and improves odour and stability. Products sold as naphthas find their use as solvents, thinners, or as carriers. Naphthas could be classified between aliphatic (paraffinic) naphthas and aromatic types. Aliphatic naphthas are relatively low in odor and toxicity and low in solvent power. These are used in processing of soyabeans for oil extraction, by dry cleaners, as a carrier in printing inks. Aromatic naphthas are the high solvency type. The main components are toluene and xylenes. These are used as thinners for paints and varnishes. Rubber industry also uses naphtha as solvents. Leather industry uses them to degrease the skin, metal industry to degrease metals. naphthas also find usage in floor waxes, furniture waxes, shoe polishes and metal polishes. And offcourse naphtha is used in the manufacture of synthetic (artificial) resins. Pure naphtha is highly explosive when exposed to an open flame.

Shrink Packaging

Packaging is increasingly gaining importance in marketing end-products. Its importance can be guaged by the fact that it features prominently along with Product, Price, Promotion, Place: the other four 'P's required for the success of a product. With mini supermarkets and departmental stores mushrooming everywhere, for enhancing convenience to the Indian society, a packaging which projects and protects a product has gained immense popularity. A product packed in a glass-like transparent plastic film certainly improves its chances for increased acceptance and sales.Shrink wrapping or packaging which adheres tightly over the contours of a product, irrespective of its shape, is a well known application developed in the economically advanced countries.Shrink wrapping can easily be divided into two basic categories:-


Collation film or thin shrink film
Industrial or Heavy duty thick shrink film



Thin shrink film is essentially used for consumer products, which are directly marketed to the public, through supermarkets, mini supermarkets or departmental stores. It can consist of packing for a single unit or multiple units.

Heavy duty shrink film is designed to pack industrial items or produce, which are essentially marketed to industries rather than direct consumers.



These two products differ in some critical requirements of the basic film properties.Thin film - should have an excellent clarity to achieve the desired aesthetics and image of a product.Heavy duty industrial shrink film requires an excellent impact strength and other mechanical properties to protect products in transportation. Clarity is not considered to be essential.



Polymers suitable for thin film are essentially required to provide excellent clarity. PVC in comparison to PE has better clarity and is therfore more suitable for such applications. On the other hand, PE films provide excellent impact strength and hence are more suitable for heavy duty shrink film applications. Recently, several polyolefinic film compositions with excellent clarity have been developed, which could replace PVC in the thin shrink film segment.



The basic principle of shrink wrapping of plastic films revolves around the fact that all polymer molecules relax after being stressed. The polymers which have a low relaxation behaviour would trend to shrink better compared to those which relax very quickly. In general, amorphous polymers such as PVC, shrink very easily.On the other hand, crystalline polymers like HDPE or PP shrink slowly or shrink less. Among Polyolefins, LDPE, having the least crystallinity, is more suited for shrink film application. Besides, LDPE being very flexible, provides the desired impact / toughness for heavy duty shrink film.



Shrink film requires an application of heat during packing process to relax molecules and thereby induce shrinkability. An application of heat can be made by manual, semi automatic and fully automatic equipments, essentially depending upon the size and complexity of product packaging and speed of conversion. A simplest mode of heating can be attained by the use of Heat guns, similar to dryers used to dry hair. These are very economical and can be used for packing of articles at a lower conversion rate. Indeed, to achieve higher productivity and reduce labour costs, semi automatic or fully automatic shrink tunnels or chambers are required. For heavy duty shrink film, which is used for packing of industrial products, sophisticated shrink tunnels equipments are essential.

What is Roto Moulding / Rotational Moulding?

This process is used principally to form hollow articles, although imaginative designers have moulded products such as tool boxes and pallets which are a major departure from the more famililar footballs and tanks. In the method, a measured quantity of liquid (plastisol) or powdered plastic is mixed with catalyst and fed into the open mold as quickly as possible which is then rotated relatively slowly about two axis in an environment above the melt temperature of the plastic (usually 230°C to 400°C). The speeds of rotation are usually less than 30 rpm. The speed ratio between the two axis of rotation (major or minor) is important and is selected to suit particular product shapes. The ratio can vary from 10:1 to 1:10.


When the plastic has coated the inside of the mould because of gravitational & centrifugal forces, from the rotation of the mould, the latter is cooled, while it is still rotating to solidify the plastic. The mould halves are then opened and the moulding is removed. Cycle times are relatively slow (3-20 mins), but as this is a low pressure process, the equipment is simple and the moulds are very inexpensive because, no cooling channels are required inside the mould, when compared with, say, an injection mould for a similar size of moulding.
To help increase production rates, multi-station machines are available. For example a three mould system can have one mould being charged with material, one mould rotating in the oven and one mould in the cooling zone. Mould heating may be achieved by one of a variety of methods which include direct gas flamed, hot air, and infra-red. Some newer types of machines have the mould heated by synthetic oil flowing in a jacket around the mould. Cooling is normally achieved by the air or a water spray, but in the liquid heated machine the circulation oil is also used for cooling.


The wall thickness of the product is controlled by the amount of powder put into the mould. There is no waste in the form of sprues,runners, and so on, and therefore no trimming is required. But in some cases part of the moulding may be cut off and discarded, for example to produce an open water tank. In many cases the mould is designed so that the container and its lid are moulded in one piece and when they are cut apart the lid fits over the rim of the container. Dust bins complete with their lids can be moulded in this way.


Not all plastics are suitable for rotational moulding. The most commonly used materials are PVC plastisol and powdered polyethylene HDPE, LLDPE but acetal, nylon (types 6,11, and 12), cellulosics, ionomers, polycarbonate, and EVA have also been used. Nylon and polycarbonate usually require an inert atmosphere in the mould to prevent embrittlement. The MFI and material density characteristics are taken into account for the selection of raw materials.


Although rotational moulding is labour intensive and has slow cycle times, its simplicity and inexpensive moulds are making it one of the expanding sectors of polymer processing. The moulds are usually made from aluminium or sheet metal, so they can be fabricated quickly and alterations are not a problem. The process also lends itself to short runs and, in general, it is competitive with blow moulding and injection moulding in many areas-particularly for larger products. The unique feature of the process that one can manufacture a product from different colours at a time rather in a single cycle in multicavity.


Application areas for rotational mouldilng vary from very large storage tanks (12,000 gallons in one case) to missile nose cones. Typical products include boats, chairs, traffic cones, petrol tanks, barrels, and toys.

What you should know about Carbon black before using it in plastics

Carbon black is used in large quantity in rubbers and is a very important additive for rubbers to improve their mechanical properties by reinforcement. However, it provides the three most important properties to plastic.

Light protection
Coloring
Conductivity enhancement

But before we look at the above properties, let us look at what carbon blacks are.Carbon blacks are obtained by cracking oil or gas organic feedstocks in a limited oxygen atmosphere. They can be obtained via several process channels starting from gas, leading to acidic and slow curing carbon blacks.
Furnace starting from oil - Most commonly used today for rubber reinforcement.
Thermal starting from gas - The obtained carbon blacks are weakly or non-reinforcing.
Acetylene starting from acetylene - These carbon blacks are used to make conductive polymers.Carbon black produced from gas known as channel black has the lowest purity while the thermal carbon black can have purity as high as 99%. Physically, the carbon blacks are organized in three structural levels:
Primary particles characterized by size ranging from 10 to 500 nm.
Aggregates of particles characterized by size ranging from 40 to 600 nm.
Agglomerates of aggregates.
The basic property is the particle size (10 to 500 nm) that can be measured by direct methods or indirectly by surface area measurement such as absorption of liquids or gases: CTAB, iodine, nitrogen. Each method leads to a different value. Contrary to the CTAB index, the nitrogen absorption measures both porosity (inaccessible for rubber) and external surface area. Current surface areas range from 10 m2/g to 150 m2/g.The smallest particle sizes lead to the highest surface areas and the corresponding carbon blacks are the most reinforcing but also the most difficult to disperse.The aggregate sizes (40 to 600 nm) and structures (voids, number of particles) are characterized by oil absorption, currently dibutylphthalate or DBP absorption with values ranging from 30 to 150 cm3/100 g.

The high levels of carbon black used to reinforce rubbers explain their black color and for majority of grades, the absorption of UV and light protection. Carbon blacks can be used at much lower concentrations to provide a grey or black coloring, and still protect the rubber or plastic.

HDPE Agrishade Nets offer higher profitability to entrepreneurs

The word Agrishade Net is termed for a net which prevents excess sunlight from entering into the plants and to retain moisture levels in the soil for proper growth of these plants leads to an increase in productivity (yield) of the plants.• Agrishade Nets are the best way to protect your crops against the ravages of nature : solar radiation, frost, wind and birds.• Agrishade Nets as : – Bird protection net. – Mulch mat (weed control mat). – Scaffolding net.Advantages of HDPE Shade Net• Light Control : Enhances photosynthesis by manipulating the amount and quality of light by means of various densities of netting.• Temperature Control : Improves productivity by moderating extremes of temperatures. Prevents sun burn and frost damage. The special knitted construction “breathes”, allowing hot air to escape.• Saves water upto 60%• Saves on fertilizer costs• Reduces wind, hail, bird and insect damage to crops.• High density polyethylene will not decay or absorb moisture.• Ultra-violet ray stabilization prevents degradation by sunlight.Useful benefits• Air movement is restricted, thus reducing wind damage to the crop and evaporation of soil moisture.• Air beneath the shade cloth stays humid which is of further benefit to the plant.• Shade cloth provides a physical barrier against hail and heavy rain and keeps many birds and insects off the crop.(Source : http://www.protect-o-net.com/)These agrishade nets are made up of high density polyethylene.Achieving monetary gains with high value-added products coupled with high volume business needs to be looked at by existing processors of HDPE woven sacks. Adding one more product leads to diversification and helps these processors to increase the product mix and would result into a higher average selling price- translating into a higher net profitability. Diversification brings in a lesser dependence on a single product helping entrepreneurs to achieve a higher net profitability leading to a flexibility to offer multifarious products to multiple enduses. This higher net profitability would lead to more number of entrants into this business resulting into a higher profitability for farmers. Using these high density polyethylene agrishade nets by farmers would result into a higher productivity (yield) of plants bringing in a higher net profitability for farmers. One would start thinking about this versatile polymer and versatile plastic product which has helped farmers with a product which offers higher productivity (yield) of plants.Versatility of polymer capable of producing a broad horizon of plastic products such as high density polyethylene agrishade nets would bring in benefits to both entrepreneurs and farmers. Higher productivity (yield) to farmers would bring in a growth in agriculture sector leading to an economic growth of the country. Also, higher net profitability to entrepreneurs would bring in an Indian Industry with high returns in business.Agribusiness in India• Largest producer of milk, fruits, pulses, cashew nuts, coconuts and tea in the world.• Second largest producer of rice and wheat in the world, and fourth largest in coarse grains.• Amongst the top 3 producers in the world - Poultry products, - Fruits & vegetables - Spices.• One of the largest producer of – Cotton Sugar, Sugarcane Peanuts.• 25% of GDP.• 64% Employment.• 18% of India’s exports.(Source : CMIE)Promotion of plasticulture products bringing in a higher yield (productivity) of plants helping Indian Industry to a grow at a fast pace. Plastics in agriculture involves products such as mulch film, drip irrigation pipes, raschel bags and agrishade nets helping entrepreneurs to include more number of plastic products into their business. Agribusiness in India(Source : http://www.protect-o-net.com/)(Source : http://www.punebds/tl.asp)In 2007, globally, India was No.1 producer of fruits (accounting for 32 mln tons out of 370 mln tons of fruit production in the world) and No.2 producer of vegetables (India’s share is 71 mln tons out of the 473 mln tons of vegetables produced in the world). Hence a huge potential exists for HDPE Agrishade Nets which needs to be tapped in our country. (Source : http://www.punebds/tl.asp)Assuming 1 Acre cultivated land requires 6000 sq mts of HDPE Agrishade Nets or 1 Hectare requires 15,000 sq mts of HDPE Agrishade Nets and assuming 140 gms/sq mt with 75% shading and 75,000 hectares in Tamil Nadu and Karnataka amounts to a potential of 1,57,500 tpa.Net Cultivated Area in India is 1420 lac hectares.Assuming only 0.1% market penetration for HDPE Agrishade Nets, 1.4 lac hectares based on the above internet statistics, Potential for HDPE Agrishade Nets in India is 2,94,000 TPA. (Assuming only 0.1% of Net cultivated area and 1 Hectare requires 15,000 sqmts & 140 gms per sqmt with 75% shading)(Source: http://Land Use in Southern States.htm, http://PACS Programme backgrounders and discussion papers on poverty in India.htm, http://www.cseindia.org/dte-supplement/water20031115/dripping_promse.htm)Plastic processing machinery, a link between polymer and plastic product brings in versatile machinery capable of producing more than a single product on the same machinery. One such machinery is a tape extruder which can produce both agrishade nets and woven sacks from the versatile polymer, high density polyethylene. With an additional investment in knitting machines, existing high density polyethylene woven sack manufacturers can manufacture high density polyethylene agrishade nets and high density polyethylene raschel bags.