Facts about Polythene carry bags

Plastic Carry Bags are generally made out of polyethylene (polythene) which is used in contact with food stuffs, pharmaceuticals and drinking water and its use in these critical areas is approved by the regulatory authorities across the world including that in India like Bureau of Indian Standards (BIS) (Refer BIS Specification IS 10146:1982 – Reaffirmed on Feb-2003). Plastic Carry bags have contributed significantly in creating a sustainable, cost effective, energy efficient, hygienic and environmental friendly packaging system and for carrying, storing and packing various types of commodities/products including food products. The attributes, which have made the use of plastics safe and popular as a packaging material in general and as a carry bag in particular, are: • Non toxic characteristics, inertness and chemical resistance. • Excellent barrier properties and water-proof characteristics. • Safe in handling due to non-breakability and light in weight. • Transparency, allowing easy visibility of content being carried/stored/packed. • Can also be opaque to protect the content from exposure to sunlight, when required. • Resistance to bacterial and other microbial growth. • Pilfer proof characteristics etc. Plastic carry bags due to these properties ensure that the products of mass consumption are delivered to the consumers in the best, hygienic and economic fashion. Being inert in nature, they do not pose any health hazard. All plastics in general meet the requirements of both National and International standards like BIS, FDA etc. Plastic carry bags and ancillary products add convenience to day-to-day life. They are essential for packaging of bread, confectionery items, all range of Farsan/Namkeen and bakery products in view of its superior properties and cost effectiveness. All these products are very sensitive to moisture and loose taste and quality within no time. Hygroscopic edible products like sugar, salt, jaggery and many other food items susceptible to moisture cannot be effectively packed in alternative materials without sacrificing the quality or cost of packaging. Over years plastics packaging have played a major role in protecting and increasing the shelf life of these products. For carrying fish, meat, poultry and other wet food products, plastic bags are most suitable and no other alternative packaging can substitute them.

• Plastic bags generate 60% less greenhouse gas emissions than uncomposted paper bags and 79% less greenhouse gas emissions than composted paper bags. The plastic bags generate 3,097 tons of CO2 equivalents per 100 million bags, while uncomposted paper bags generate 7,621 tons, and composted paper bags generate 14, 558 tons, per 100 million paper bags. Life Cycle Inventories for Packaging, Vol. 1, SAFEL, 1998 • Plastic grocery bags consume 40% less energy during production and generate 80% less solid waste after use than paper bags. (US EPA) • Paper sacks generate 70% more air pollutants and 50 times more water pollutants than plastic bags do. US EPA. • It takes 91% less energy to recycle a kilogram of plastic than a kilogram of paper (US EPA) • Transporting 150,000 nos. plastic carry bags of minimum stipulated size (20X30 cms) of 40 micron thickness (weighing~600 kgs) would require one small tempo, whereas similar size and number of paper bags would require more than 10 such tempos for delivering the bags. Consider the extra fuel and cost it would need! A scientific comparison between paper and polyethylene is shown below: Environmental burden Polyethylene Paper Energy (GJ) for manufacture 29 67 Air pollution SO2 9.9 28.1 NOx 6.8 10.8 CHx 3.8 1.5 CO 1 6.4 Dust 0.5 3.8 Waste water burden COD 0.5 107.8 BOD 0.02 43.1 (Source: Fabbri, A in Scott, G and Gilead , D., editors, Degradable Polymers, Principles and Application, Chapman & hall, 1995, Chapt.) Moreover production of paper is dependent on availability of wood pulp for which trees have to be felled causing further environmental concern. Plastic and Jute Bags A comparison of Plastic Bags with Jute Bags in terms of Life Cycle Analysis reveals that • Energy Saving during manufacture of raw materials, production and transportation of plastic bags compared to jute bags is 81%. • Environmental Burden with respect to Air and Water pollution during Production of Raw Material and Bags for Plastic Bags and Jute bags are given below: Environmental Burden Jute Bag Plastic Bag Air Emission CO kg 54.3 0.6 CO2 kg 6610.2 760.0 SOx kg 134.8 5.2 NOx kg 68.1 4.8 CH4 kg 39.5 3.2 HCl kg 5.3 0.0 Dust kg 67.6 1.4 Water Emission Suspended Solids kg 352.3 0.2 Chlorides kg 4535.5 0.1 The environmental burdens during transportation of the finished bags are as below: Emission gm/km Excess emission for Jute bags Plastic Bags CO2 781.0 11107.3 Taken as Basis CO 4.5 64.0 Taken as Basis HC 1.1 15.6 Taken as Basis NOx 8 113.8 Taken as Basis Particulates 0.36 5.1 Taken as Basis Total regulated tail pipe emission 13.96 198.5 Taken as Basis The values are for packaging of one lac MTs of Atta. Source: Centre for Polymer, Science and Engineering, IIT - Delhi Consider the enormous environmental burden generated by Jute bags, which are not visible to naked eyes though, in comparison to Plastic Bags! Plastic and Textile Bags When plastics and textile are compared, following data is revealed: • Plastics manufacturing consumes 400 kwh/mt while composite textile mills consume 1310 kwh/mt. • Textile contributes 30% SOx (Second Highest by Any Sector) and 23% NOx (Highest by Any Sector) (Source : Warmer Bulletin, July 01) Millions of KW of energy is saved and the atmosphere is less polluted when Plastic Carry bags are used in place of Textile bags. Biodegradable/Compostable Plastic Bags Biodegradation/Composting, by definition releases CO2 and CH4 - both Green House Gases, in to the atmosphere. Moreover, process takes place only when suitable environment is available. Use of biodegradable / composting plastics is thus restricted to specific applications worldwide. What is the Real Issue? Our poor littering habits coupled with insufficient infrastructure for waste management has created the disposal problem of solid waste, including the plastic waste in the urban areas. However, available data reveals that the MSW in major cities in India contains around 5% plastics waste, balance being Paper, Compostable Matters, Sand, Silt, Sanitary Diapers and Construction Debris etc. Hence Plastic Bags cannot be singled out as the sole reason for clogging of drains. Discontinuation of Plastic bags is no solution and will rather multiply the problem many fold. This will add to the woes of common man as the so called alternatives are unviable, costly and place greater burden on the environment. To discourage illogical use and to encourage the waste pickers for collection and recycling process, the regulatory bodies have already specified the minimum thickness and size of plastic carry bags. Therefore, the challenge facing us is to improve the solid waste management system and address littering habits of masses by educating them and creating awareness. The solution lies in Segregation of Waste at Source and arrangement for Recycling of all recyclable waste. Plastics Bags are 100% recyclable.

Injection Moulding Troubleshooting Problems & its Recommendations

Brittleness
Reduce screw speed
Reduce back pressure
Reduce cylinder temperature
Check for material contamination
Dry material

Blisters
Increase back pressure
Reduce screw speed
Dry material

Excessive Flash
Increase back pressure
Reduce cylinder temperature
Reduce injection pressure
Clean mold faces
Increase clamp pressure
Check mold faces for proper fit

Gas Burns
Increase size of vent
Increase size of gate
Reduce injection speed

Poor part to part Uniformity
Check heater bands, controllers and thermocouples
Check hydraulic system for pressure variation
Check hopper for material bridging

Oversized Part
Increase mold temperature
Reduce overall cycle time
Reduce injection speed
Reduce injection and holding pressure
Reduce cylinder temperature

Silver Streaking
Increase mold temperature
Decrease screw speed
Dry material
Increase injection speed
Increase cylinder temperature

Poor Weld Lines and Poor Surface Finish
Increase cylinder temperature
Increase mold temperature
Increase injection pressure
Increase injection speed
Change gate location
Vent Mold
Clean cavity surface

Short Shots
Increase size of
- Sprue
- Runners
- Gates

Clean vents
Increase back pressure
Incorporate or enlarge venting
Increase amount of material
Increase injection pressure
Raise material temperature
Raise mold temperature
Increase injection time

Undersized Part
Increase holding time
Increase cylinder temperature
Increase size of gate
Decrease mold temperature
Increase injection and holding pressure
Increase injection speed

Sink Marks
Reduce cylinder temperature
Increase holding time
Increase holding pressure
Reduce mold temperature
Increase gate size
Increase injection pressure
Locate gates near heavy cross sections

Warping
Reduce molded in stress
- Raise molded in stress
- Reduce injection speed
- Relocate gating

Check for uneven mold temperature
Reduce temperature of ejected part
- Increase cooling time
- Lower mold temperature
Redesign ejection mechanism

Voids
Increase injection pressure
Reduce cylinder temperature
Use dry material
Increase mold temperature

Output of PE pipe can be increased significantly by air/water cooling

A new high-output extrusion die for large HDPE or PP pipe (110 to 2000 mm OD) combines water-cooling of the melt before it leaves the die with air cooling inside the pipe has been developed by Cincinnati Extrusion. The combination can either double pipe output or reduce downstream cooling length by half. The Kryos die has three parts: melt distribution, melt cooling, and shaping. The cooling and shaping parts have a number of separate chilled-water cooling loops. The large-diameter cooling section in the middle of the die has several chilled-water spirals, which make the die so large that it's mounted in its own motorized C-clamp to remove it for die changes and cleaning. The elongated final shaping stage is sectioned lengthwise into segments that have both water-cooling loops and heating for tight temperature control to maintain uniform wall thickness of the pipe. In addition to water-cooling the melt, the Kryos die sucks ambient air through the cut end of the pipe, back through the hot pipe, and out a hole in the middle of the die. This air flow renews the layer of air next to the inside surface of the pipe, which otherwise heats up and acts as an insulator. Cincinnati Extrusion calculates that energy use with its KryoSys line is less than half that for standard pipe extrusion.

The Kryos die requires an air suction unit behind the die (drawing 3 kW ) and a water chiller for the die (5 kW ), but then needs only one 9-meter vacuum calibration tank (10.5 kW ) and four 6-meter spray cooling tanks (4 kW each). Cooling-water circulation and heat exchange in all the tanks add another 122 kw, for total energy use of 156.5 kW . In a standard pipe line, downstream cooling uses one 9-meter and one 6-meter vacuum calibration tank (10.5 kW each) and ten 6-meter spray cooling tanks (4 kW each). Much higher volume of cooling-water circulation and heat exchange takes 320 kw, for total energy use of 381 kW . Heat removed by KryoSys air cooling can also be easily recycled for further energy savings. Drying and preheating plastic pellets in the hopper, for example, reduces energy consumption at the extruder by another 10%. Machine components are arranged slightly differently with KryoSys. The extruder is placed off-center from the die to allow for the air hole and suction unit behind the die. The die then feeds melt via an IRIS 40 spiral distributor at the edge of the die. Downstream spray tanks are spaced 4 to 6 ft apart, so pipe passes through ambient air (without sagging). This balances internal and external cooling. With a Kryos die, the pipe also has to be cut by a swarfless cutter to avoid sucking fines back through the hot pipe and into the suction pump.

Extruding the pipe at a lower temperature and cooling it evenly inside can improve pipe quality by reducing residual stress. The great advantage of this particular pipe die is an innovative melt cooling system inside the die. Thanks to this system, it has become possible to start cooling the melt in the die, which allows a substantial reduction in the length of the cooling section. The lower melt temperature also brings about a significant increase in viscosity at the point of exit from the die, which counteracts sagging especially in thick-walled pipes. Moreover, KryoS features a large internal aperture, which allows air cooling of the extruded melt. The KryoSys system is rounded off by a highly efficient pipe cooling section. In this aggregate, the pipe is cooled simultaneously from the outside and the inside by an ingenious combination of water and air cooling, which permits a further shortening of the cooling section. Another advantage of KryoSys is the system's great in-production energy saving potential. Thanks to its direct drive, the Rapidex high-speed extruder operates with an extremely high level of energy-efficiency. Through a reduction in the number of vacuum and spray cooling baths required for the downstream aggregates and the optimized cooling system consisting of water and air cooling, energy consumption can be cut by up to 71kW (about 27 kW are saved by the reduction in the number of circulation pumps, and about 44 kW by the fact the less water is circulated). Another source of energy savings is utilization of the heat set free by the pipe cooling system in the die. With KryoSys, this energy can be used for material pre-heating. Thus the torque of the extruder can be reduced, resulting in energy savings of up to 95 kW. By combining all of these measures, a total reduction in energy consumption of roughly 186 kW can be achieved.

With energy costs of 0.10 EUR/kWh and 6,000 operating hours per year, this adds up to about 100,000 EUR in annual savings for a single extrusion line. Kryosys lines lend themselves to the production of smooth mono-layer and multi-layer PE or PP pipes with diameters ranging from 110 to 2,000 mm. They are also suitable for the production of corrugated pipes. Total investment cost for a KryoSys line is highly competitive compared to conventional extrusion equipment.

Plastic Carry Bags are generally made out of polyethylene (polythene) which is used in contact with food stuffs, pharmaceuticals and drinking water and its use in these critical areas is approved by the regulatory authorities across the world including that in India like Bureau of Indian Standards (BIS) (Refer BIS Specification IS 10146:1982 – Reaffirmed on Feb-2003). Plastic Carry bags have contributed significantly in creating a sustainable, cost effective, energy efficient, hygienic and environmental friendly packaging system and for carrying, storing and packing various types of commodities/products including food products. The attributes, which have made the use of plastics safe and popular as a packaging material in general and as a carry bag in particular, are:

• Non toxic characteristics, inertness and chemical resistance.

• Excellent barrier properties and water-proof characteristics.

• Safe in handling due to non-breakability and light in weight.

• Transparency, allowing easy visibility of content being carried/stored/packed.

• Can also be opaque to protect the content from exposure to sunlight, when required.

• Resistance to bacterial and other microbial growth.

• Pilfer proof characteristics etc.

Plastic carry bags due to these properties ensure that the products of mass consumption are delivered to the consumers in the best, hygienic and economic fashion. Being inert in nature, they do not pose any health hazard. All plastics in general meet the requirements of both National and International standards like BIS, FDA etc.Plastic carry bags and ancillary products add convenience to day-to-day life. They are essential for packaging of bread, confectionery items, all range of Farsan/Namkeen and bakery products in view of its superior properties and cost effectiveness. All these products are very sensitive to moisture and loose taste and quality within no time. Hygroscopic edible products like sugar, salt, jaggery and many other food items susceptible to moisture cannot be effectively packed in alternative materials without sacrificing the quality or cost of packaging. Over years plastics packaging have played a major role in protecting and increasing the shelf life of these products. For carrying fish, meat, poultry and other wet food products, plastic bags are most suitable and no other alternative packaging can substitute them.
• Plastic bags generate 60% less greenhouse gas emissions than uncomposted paper bags and 79% less greenhouse gas emissions than composted paper bags. The plastic bags generate 3,097 tons of CO2 equivalents per 100 million bags, while uncomposted paper bags generate 7,621 tons, and composted paper bags generate 14, 558 tons, per 100 million paper bags. Life Cycle Inventories for Packaging, Vol. 1, SAFEL, 1998
• Plastic grocery bags consume 40% less energy during production and generate 80% less solid waste after use than paper bags. (US EPA)
• Paper sacks generate 70% more air pollutants and 50 times more water pollutants than plastic bags do. US EPA.
• It takes 91% less energy to recycle a kilogram of plastic than a kilogram of paper (US EPA)
• Transporting 150,000 nos. plastic carry bags of minimum stipulated size (20X30 cms) of 40 micron thickness (weighing~600 kgs) would require one small tempo, whereas similar size and number of paper bags would require more than 10 such tempos for delivering the bags. Consider the extra fuel and cost it would need!
Moreover production of paper is dependent on availability of wood pulp for which trees have to be felled causing further environmental concern.Plastic and Jute BagsA comparison of Plastic Bags with Jute Bags in terms of Life Cycle Analysis reveals that
• Energy Saving during manufacture of raw materials, production and transportation of plastic bags compared to jute bags is 81%.
• Environmental Burden with respect to Air and Water pollution during Production of Raw Material and Bags for Plastic Bags and Jute bags are given below:


Consider the enormous environmental burden generated by Jute bags, which are not visible to naked eyes though, in comparison to Plastic Bags!Plastic and Textile Bags When plastics and textile are compared, following data is revealed:
• Plastics manufacturing consumes 400 kwh/mt while composite textile mills consume 1310 kwh/mt.
• Textile contributes 30% SOx (Second Highest by Any Sector) and 23% NOx (Highest by Any Sector) (Source : Warmer Bulletin, July 01) Millions of KW of energy is saved and the atmosphere is less polluted when Plastic Carry bags are used in place of Textile bags.
Biodegradable/Compostable Plastic Bags Biodegradation/Composting, by definition releases CO2 and CH4 - both Green House Gases, in to the atmosphere.

Moreover, process takes place only when suitable environment is available. Use of biodegradable / composting plastics is thus restricted to specific applications worldwide. What is the Real Issue? Our poor littering habits coupled with insufficient infrastructure for waste management has created the disposal problem of solid waste, including the plastic waste in the urban areas. However, available data reveals that the MSW in major cities in India contains around 5% plastics waste, balance being Paper, Compostable Matters, Sand, Silt, Sanitary Diapers and Construction Debris etc. Hence Plastic Bags cannot be singled out as the sole reason for clogging of drains.Discontinuation of Plastic bags is no solution and will rather multiply the problem many fold. This will add to the woes of common man as the so called alternatives are unviable, costly and place greater burden on the environment. To discourage illogical use and to encourage the waste pickers for collection and recycling process, the regulatory bodies have already specified the minimum thickness and size of plastic carry bags. Therefore, the challenge facing us is to improve the solid waste management system and address littering habits of masses by educating them and creating awareness. The solution lies in Segregation of Waste at Source and arrangement for Recycling of all recyclable waste. Plastics Bags are 100% recyclable.

Wrinkles in film can be eliminated by simple measures

Wrinkles are a major cause of defects in extrusion winding and converting, especially with thinner films, which are much more wrinkle-prone than thick ones. The cause of most wrinkles is located close to the roller where the wrinkle first appears and can be identified by looking at the orientation and pattern of the wrinkle. By the time the web gets to the winder, it may have wrinkles from several different sources, though it’s not unusual for 90% of wrinkles to be caused by one or two machine components. Shadows are wrinkles waiting to happen when a slight change in product grade or web tension pushes the shadow into a crease. A portable lamp helps bring the shadows out more clearly. Wrinkles are tension-sensitive, though tension is seldom the root cause. The few wrinkles caused by tension are primarily in very low-modulus elastomeric films. Another powerful diagnostic technique is to slow the machine down to thread-up speed, if the process allows it. Operators often ignore wrinkles that occur during thread-up because “they go away when you speed up,” because air lubricates webs, reducing traction on rollers. Wrinkles come with lots of colorful nicknames, but they usually fall into one of five categories: MD or diagonal, symmetrical or asymmetrical, or CD.
• Symmetrical MD wrinkles are nearly parallel and uniformly spaced, with narrower spacing between wrinkles in thin film and wider in thick film. They are common in flexible films when the web becomes wider than it originally was. In very stretchy materials, this expansion can be caused by a tension drop in one web span vs the preceding span. Constant tension helps to eliminate wrinkles. Thin idler rollers with a lot of deflection can also cause film to stretch. The use of an idler roller with less deflection or shallower grooves helps to reduce wrinkles. Sometimes the problem is part of the process. If film is sent through an oven, heat causes the film to expand. For hygroscopic films like nylon or PET, high humidity or water-based inks or adhesives also can cause expansion. The least aggressive option, which is often adequate, is to flatten the web by routing it over a large-diameter roller, a lightly tensioned roller, a slippery roller, or some combination of these rollers. As a last resort, spreading can be used- not merely installing a spreader, but also adjusting it properly.
• Asymmetrical MD wrinkles are caused by the same things as symmetrical MD wrinkles, except that the even pattern is disrupted somewhere, so several MD troughs collect in an open span into a single bulge or crease. Asymmetrical MD wrinkles retain their orientation, but may move around and even cross over each other.Typically, more things are happening to cause asymmetrical wrinkles than symmetrical ones. A single wrinkle that stubbornly stays in one place, as if it were stuck in a groove, may indeed be stuck in a valley or bulge in a roller. Such roller variations are correctible with better maintenance and housekeeping. Lack of gauge uniformity in the web can also be a cause.
• Symmetrical diagonal wrinkles (bow wrinkles) are oriented inward from the edge of the film at an angle. They fade and disappear in the center of the web, forming a symmetrical arrowhead. The steeper the angle, the more uneven the pulling forces. The cause commonly is something such as a roller or the web itself that is “smile” shaped.The curve may come from excessive roller deflection, caused by a roller too small in diameter for the web width or tension. Larger-diameter roller helps in reducing the wrinkles. Mismatch of the nip-roller crown to tension load can also cause bowing. Spreading or flattening can also be an effective remedy. But spreading with too much bow or improper orientation can also cause these wrinkles. The spreaders should be adjusted properly.
• symmetrical diagonal wrinkles (lightning-bolt wrinkles) are a single band of wrinkles oriented at an angle to the machine direction. They all point the same way and may favor one side of the web. They tend to be evenly spaced and sometimes “walk” sideways. The usual cause is something such as a roller or the film itself that is crooked.
• A misaligned web-handling roller is a common cause of asymmetrical diagonal wrinkles. These wrinkles point toward the narrower side of the misalignment and walk toward the wide side. Roller diameter variation from side to side, nip-pressure variation, and uneven pull from narrow drive rollers or edge-trim tension can also cause these wrinkles.
• CD wrinkles, known as buckles, occur primarily during rewinding. They are caused by loose winding followed by tighter winding and become apparent in the edge of a roll as a compressed wave pattern. The problem may be insufficient drum torque, temporary loss of web tension (possibly at a splice), malfunctioning tension control, too rapid braking of roll speed, or binding of the core shaft or rider roll slides. The solutions are to provide smooth tension as roll radius changes; to start, stop, or make splices under tension; and to ensure that slides move freely

New methods for higher loading of fillers without causing dispersion related problems

Increasing polymer prices, driven by rising crude oil prices are driving development of newer methods of addition of higher levels of fillers and glass fibers. Plastics additive suppliers and equipment manufacturers have developed new technologies that enable processors to maximize levels of fillers in their formulations and minimize some of the problems that can result from high filler levels.In PVC pipes, calcium carbonate is added to lower costs, increase stiffness and improve toughness and processing properties. At filler levels of 20-30 phr (parts per hundred parts) problems begin to arise during processing. These include separation of calcium carbonate and PVC particles during pneumatic conveying of dry blends to intermediate storage silos, as well as formation of calcium carbonate deposits on the walls of hot mixers. In a collaborative effort, calcium carbonate supplier Omya International AG and plastics machinery manufacturer Rollepaal recently found a way to overcome these difficulties. Their method consisted of mixing calcium carbonate uniformly with a PVC-calcium carbonate dry blend in a cold immediately prior to feeding the mixture into the extruder. This procedure, which was demonstrated at the K 2007 show, eliminated the particle segregation problem, as well as the deposits of calcium carbonate that had separated from the PVC in the hot mixer. The result was that compact PVC pipes (160 mm dia and 4 mm wall thickness) could be extruded with calcium carbonate loadings of up to 45 phr. In addition, 200 mm foam-core PVC pipes with 5.9 mm-thick walls could be extruded containing up to 40 phr calcium carbonate. Glass-reinforced plastics (GRP) are another area in which higher loadings of fillers can be employed as a result of technological advances. One of the recent trends in GRP - including resin transfer molding (RTP) and vacuum film infusion – is the use of resins filled with glass microspheres. These formulations decrease consumption of expensive resin, reduce part weight, and improve surface finish and thermal and acoustic properties. However, because GRP is a closed-mold process, the required reinforcing fabrics often get highly compressed, limiting the flow of highly filled resins. One solution to this problem is to use a reinforcing fabric design that resists deformation during molding so that even highly filled or viscous resins can permeate it freely. One such high-flow fabric has been developed by Scott & Fyfe Ltd. (Fife, U.K.) and its subsidiary Flemings Textiles Ltd. It consists of 300 gsm chopped-glass fibers stitched-bonded to an engineered core designed to maximize resin blow. The chopped fibers, which are 50 mm in length, have a silane finish to promote good wetting of fibers. The core is intended for laminates in the 2-4 mm range. The new reinforcing fiber, known as Polymat Hi-Flow, allows the use of highly filled unsaturated polyester – loaded with 10% glass microspheres and 60% chalk by weight – that could not be used with conventional reinforcing fabrics. Use of this formulation with the new mat reduces resin infusion time by 50%. Meanwhile, the 10% loading of microspheres reduces part weight by 40%. In a recent technical report, Scott & Fyfe estimated that replacement of unsaturated polyester with even 5% of glass microspheres by volume could save up to 15% on resin costs. Wood-plastic composites have also benefited from new processing methods that increase loadings of fillers. Generally, the wood flour or particles used in these composites is incorporated at levels between 40-60% by weight, with some applications using up to 70%. While there are good economic incentives to use even higher levels of wood in some composites, problems arise with conventional extruders when the content is over 70%. At lower levels of wood, the wood and polymers can first be pelletized or agglomerated prior to feeding into the machine. For higher wood levels, new systems have been introduced over the past few years that allow direct addition to the extruder of wood fiber, chips or powder, along with the carrier resins. Specially configured counter-rotating twin-screw designs in these machines reduce the shear forces that can damage wood fibers. The units also include venting systems for the volatiles emitted by the wood. Such systems have made it possible to process highly filled materials. The driving force for adding more filler to polymers remains primarily economic. But the resulting improvements in quality, durability and appearance and a host of novel properties are also promoting this trend.

Purging compound

Purging compound reduce machine downtime & increases productivity. Effective cleaning of plastic processing equipment is vital for keeping the machinery running productively and free from trouble.

There are several occasions that call for purging & cleaning processing equipment, including colour changes, resin changes, formulation changes & routine shutdown and maintenance. Ensuring that the machinery is cleaned thoroughly and effectively is critical for quality control and in extending the operating life of the machinery. Although breaking down a large extruder and painstakingly cleaning it by hand is thorough and effective, increasing pressures in the market place can make this method a strain on productivity. For example, just-in-time delivery demands result in greater frequency of resin and colour changes. In addition, there is always the need to manage bottom-line costs to stay competitive and profitable. Machine downtime is neither competitive nor profitable to the processors.

The use of commercial purging compounds is helping processors to meet today`s pressures by minimizing machine downtime and boosting productivity. A purging compound is introduced to the system to expunge a colour, resin or formulation before a change over or shutdown. Purging compounds are particularly helpful in preventing streaking, caused by bits of previously run colour becoming trapped in a negative flow area. Since there is not enough physical turbulence in the area to remove colour, the nest material processed picks up the trace amounts of the colour and causes a streak in the new product. The streaking will continue until the trapped colours is flushed away by the next resin.


If the streaking occurs in the same lo9cation, then the entrapment is probably closed to the die. If streaking is random, then the colour is likely trapped in the barrel or feed nozzle of the machine. Inconsistent material due to colour is considered scrap and represents wasted material and non-productive time. Purging compound are designed to remove all traces of the previous colour or resin, allowing the processor to resume full production sooner and with little, if any, scrap.

Processor using purging products may still break down a machine for manual cleaning however, pre-cleaning with the purging compound saves a significant amount of time, frequently 50% or more. This bolsters the company`s capability to meet their requirements of its customers.

In addition to cleaning of the previous colour, resin, or formulation, purging compounds are also effective in removing black specs (carbon buildup). These can be caused by any number of reasons such as hot temperature spots in the machine, degrading of polymers, separation of additives, fillers and colour concentrates from the carrier, dead spots or negative flow area in the barrel, mixing area or die, regular start up & shut down, or a lack of regular preventative maintenance. Like shale rock, the carbon buildup will break into pieces and be moved forward by the screw, only to be displayed as unwanted black spec in the finished palatalized product.
Purging compounds – the scrubbing granules used in their formulation safely penetrates into the dead spots and hot spots in the machine to break away and remove the carbon build up, including layers of separated additives and degraded polymers. This mechanical, non abrasive action will not damage the surface of the screw, barrel, or any metal components or tolerance of the plastic processing equipment.

Although there are various hybrid sold, commercial purging compounds are available in three primary types.

1. Chemical


2. Mechanical / Abrasive


3. Mechanical / non abrasive

Usage of purging compound may it be simple LDPE or complex Nylon material, following benefits can be obtained:

• Machinery can be cleaned in very short time.


• Saving of costly raw material


• Minimum rejection of the final product


• Material can be grounded and used upto 2 or 3 times.