A whale’s tale: puzzling marine compounds are natural
An 85-year-old vial of oil from a whaling ship has revealed that a mysterious group of organic chemicals resembling human-made compounds are naturally produced in the sea.
A decade ago, scientists monitoring marine mammals’ flesh for pollutants began finding unknown organic compounds containing the halogen atoms bromine and chlorine. More than 20 such compounds were eventually revealed. That raised alarms because the compounds, as complex halogenated chemicals, structurally resemble the pesticide DDT and polychlorinated biphenyls (PCBs), which were once used in flame retardants.
Manufacture of those and similar chemicals began in the 1930s. But their production and use were banned in most countries decades ago, after they were found to be deadly pollutants. Because halogenated compounds break down extremely slowly, they persist in soil and water and accumulate in animal flesh.
Researchers wondered whether the recently discovered organic chemicals were manufactured or produced naturally. Symbiotic bacteria in ocean sponges, for example, produce chemicals similar to DDT and PCBs that deter fungal growth.
To investigate, Emma L. Teuten of the University of Plymouth in England and Christopher M. Reddy of the Woods Hole (Mass.) Oceanographic Institution analyzed a whale-oil sample from 1921, before industry produced the first halogenated chemicals.
Their sample came from ajar of the translucent, yellow, odorless oil found on the Charles W. Morgan, one of the last whaling ships in operation. The ship is now preserved and on display in Mystic, Conn. “We were incredibly lucky to acquire it,” Reddy says.
The scientists found 11 of the organic compounds in the whale oil. Because of the oil’s age, the 11 compounds must have been produced naturally, the scientists conclude in their report online and in an upcoming Environmental Pollution.
“This by no means puts the chemical industry off the book,” Reddy says. Industry will probably be pleased to hear that it isn’t responsible for the cleanup of additional compounds, he says, but the study “doesn’t say that Monsanto, the main producer of PCBs, is not responsible for PCBs that are found in the environment.”
The researchers argue that the naturally occurring compounds can shed light on the fates of the similar human-made ones. The recently discovered compounds must have been around far longer than DDT or PCBs, Teuten says, so researchers may be able to study the natural halogenated compounds to find out how industrial chemicals will continue to affect the environment.
Teuten and her colleagues say that they hope to determine where the new compounds are coming from and why they are being produced. The researchers are just beginning work to find out whether the compounds are toxic.
“I think the study is fantastic,” says Gordon W. Gribble of Dartmouth College in Hanover, N.H. Their work “really does show that nature makes these compounds.”.
Polyacetal Compounds provide ESD protection. Compounds
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A whale’s tale: puzzling marine compounds are natural
An 85-year-old vial of oil from a whaling ship has revealed that a mysterious group of organic chemicals resembling human-made compounds are naturally produced in the sea.
A decade ago, scientists monitoring marine mammals’ flesh for pollutants began finding unknown organic compounds containing the halogen atoms bromine and chlorine. More than 20 such compounds were eventually revealed. That raised alarms because the compounds, as complex halogenated chemicals, structurally resemble the pesticide DDT and polychlorinated biphenyls (PCBs), which were once used in flame retardants.
Manufacture of those and similar chemicals began in the 1930s. But their production and use were banned in most countries decades ago, after they were found to be deadly pollutants. Because halogenated compounds break down extremely slowly, they persist in soil and water and accumulate in animal flesh.
Researchers wondered whether the recently discovered organic chemicals were manufactured or produced naturally. Symbiotic bacteria in ocean sponges, for example, produce chemicals similar to DDT and PCBs that deter fungal growth.
To investigate, Emma L. Teuten of the University of Plymouth in England and Christopher M. Reddy of the Woods Hole (Mass.) Oceanographic Institution analyzed a whale-oil sample from 1921, before industry produced the first halogenated chemicals.
Their sample came from ajar of the translucent, yellow, odorless oil found on the Charles W. Morgan, one of the last whaling ships in operation. The ship is now preserved and on display in Mystic, Conn. “We were incredibly lucky to acquire it,” Reddy says.
The scientists found 11 of the organic compounds in the whale oil. Because of the oil’s age, the 11 compounds must have been produced naturally, the scientists conclude in their report online and in an upcoming Environmental Pollution.
“This by no means puts the chemical industry off the book,” Reddy says. Industry will probably be pleased to hear that it isn’t responsible for the cleanup of additional compounds, he says, but the study “doesn’t say that Monsanto, the main producer of PCBs, is not responsible for PCBs that are found in the environment.”
The researchers argue that the naturally occurring compounds can shed light on the fates of the similar human-made ones. The recently discovered compounds must have been around far longer than DDT or PCBs, Teuten says, so researchers may be able to study the natural halogenated compounds to find out how industrial chemicals will continue to affect the environment.
Teuten and her colleagues say that they hope to determine where the new compounds are coming from and why they are being produced. The researchers are just beginning work to find out whether the compounds are toxic.
“I think the study is fantastic,” says Gordon W. Gribble of Dartmouth College in Hanover, N.H. Their work “really does show that nature makes these compounds.”.
Molding Study Puts Purging Costs in Perspective
As molders become more cost conscious and business savvy, practices and products that were not standard procedure in the past are under increasing consideration. One such example is the use of purging compounds rather than regrind to cut down the time between color and resin changes and to reduce the scrap that can build up as a result of incomplete purging.
According to Shuman Plastics, makers of Dyna–Purge, regrind resin was never designed to clean process equipment. “While it may remove some of the offending resin,” says Tim Cutler, business manager, “it will not clean carbon deposits and negative flow areas. Regrind has more value being reworked into finished parts or sold as surplus.”
To illustrate that the use of purging compound is no longer a luxury, Cutler sometimes takes potential customers through a cost–to–purge analysis (see Calculate Your Cost to Purge). “Although regrind looks like a bargain, it ends up costing processors more in terms of time and labor,” he says. “Commercial purging products work faster using less material.”
Color changes–such as going from dark blue to neon pink using the neat resin as a purge produced up to 400 to 500 scrap parts.
Why is the need to purge quickly and effectively rising among custom molders? Cutler believes JIT demands are one reason, calling for more frequent resin and color changes. Also, molders are no longer tolerant of the amount of scrap produced by ineffective purging methods.
It is important to note that there are many possible combinations of resin, equipment, and processing conditions, and that no one product, particularly regrind, can meet the requirements for all of these situations. As a result, purging compound suppliers should offer numerous products to fit different applications.
Field Use
To determine the effectiveness, economy, and ease of use of the nine most widely promoted purging compounds currently available on the market, Shuman Plastics commissioned a third-party independent study. The lab that conducted the study either purchased or obtained samples of the best grade from each supplier to purge ABS, PC, and nylon 6/6. All trials were run on an 83–ton Battenfeld press with a cold runner mold.
Each trial was identical, and included a molding step with black resin, a purging step per the supplier’s instructions until clean, and a post purge with natural resin until purging compound is eliminated and the machine is able to run production-quality parts. Actual cost to purge for each trial was then calculated using the cost-to-purge analysis sheet.
| Table 1: Results of Independent study comparing costs of purging compounds |
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| Purging Compound | Mechanical/ nonabrasive | Mechanical/ abrasive | Chemical/ mechanical | Chemical |
| Resin type** | ||||
| ABS | $6.67 | $5.94 | $7.44 | $15.82 |
| PC | $7.07 | $6.18 | $7.47 | $13.54 |
| Nylon | $5.12 | $9.26 | $7.88 | $13.83 |
| Average cost | $6.29 | $7.13 | $7.60 | $14.40 |
| *purging compound prices based on minimum quantity **virgin resin prices per lb: ABS $.73; PC $1.70; nylon $1.61; July 2001 Plastics News Note: Study assumes combined, average machine and labor cost of $54/hr |
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Although Shuman’s Dyna–Purge mechanical/nonabrasive product ranked first overall for economy, Cutler says, “What’s most important is that molders who see this chart now realize that the commercial alternatives to homemade or regrind purging are actually more cost effective.”
Bob Williams, injection molding manager for Aakron Rule, a New York-based custom molder, recently sampled Dyna–Purge for a troublesome application. Aakron Rule produces nine different colors of the Flyer, a polypropylene aerodynamic throwing disk, at a rate of approximately 2000 per day. The disks are molded on a 375–ton Cincinnati Milacron press using a two-cavity hot runner mold.
After the trial with a purging compound (Dyna–Purge P), Aakron Rule reduced scrap significantly and cut downtime by 75 percent.
This project required an extensive amount of downtime and there was a good deal of waste associated with each color change. In order to purge the old color out, Williams formerly used approximately 110 lb of PP. This took at least 2 hours to run and resulted in 400 to 500 defective parts being produced. As a result, it cost approximately $150 in lost material and labor every time the color changed. On an annualized basis, this equates to almost $8000 in purging costs.
Using 15 lb of Dyna–Purge P, Aakron Rule was able to clean out both the barrel and hot runner system in less than 30 minutes. This represented a significant savings, bringing the entire purging cost down to $70 per purge, with a $4000 annual savings or a 53 percent cost reduction vs. purging with its own resin.
Purging compounds reduce machine downtime and increase productivity for compounders
There are several occasions that call for purging and cleaning processing equipment, including colour changes, and routine shutdown and maintenance. Ensuring that equipment 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 marketplace 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 a compounder’s operation.
The use of commercial purging compounds is helping compounders 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 changeover or shutdown. Purging compounds are particularly helpful in preventing streaking, caused by bits of a previously run colour becoming trapped in a negative flow area. Since there is not enough physical turbulence in the area to remove the colour, the next material processed picks up trace amounts of the colour and causes a streak in the new product. The streaking will continue until the trapped colour is flushed away by the next resin.
Dyna-Purge purging compound
If the streaking occurs in the same location, then the entrapment is probably close to the die. If the streaking is random, then the old 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 compounds 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.
Compounders 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 per cent or more. This bolsters the company’s capability to meet the requirements of its customers.
In addition to cleaning out the previous colour, resin, or formulation, purging compounds are also effective in removing black specks (carbon buildup). These can be caused by any number of reasons such as hot temperature spots in the machine, degradation of polymers, separation of additives, fillers and colour concentrates from the carrier, dead spots or negative flow areas in the barrel, mixing area or die, regular start-up and shutdown, 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 specks in the finished pelletized product.
According to Shuman Plastics, Inc., manufacturer of Dyna-Purge purging compounds, the scrubbing granules used in their formulations safely penetrate into the dead spots and hot spots in the machine to break away and remove carbon buildup, 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 tolerances of the plastic processing equipment. Although there are various hybrids sold, commercial purging compounds are available in three primary types.
Chemical
A chemical purging compound is a liquid or solid concentrate that is typically let down into a universal carrier (PE or PP) or the next resin. There are also solid chemical purging compunds that are supplied as ready-to-run pre-blends. The purging compound is introduced into the machine and allowed to soak in the barrel for a specified time period at adjusted temperatures. The screw is stopped and a chemical reaction occurs that modifies and shortens the molecular chain of the resident resin, allowing the now altered resin to be flushed out. This can be a very effective purging process, but chemical purges can take longer because of soaking time, and usually entail a higher cost per kg/lb. than other types. Some chemical purging agents may release ammonia or other fumes and polymer breakdown can expose equipment to caustic acids that can cause pitting and wear. If the chemical needs to be let down into the resin, the carrying cost of the resin and blending time, as well as machine adjustments, are considered hidden costs.
Mechanical/abrasive
Mechanical/abrasive compounds are concentrates or pre-blended, formulated with glass and/or inert fillers such as clay, calcium, talc or TiO2. These purge aggressively and effectively by scouring the barrel and screw. But the fillers can cause wear on the critical tolerances of the screw and barrel.
Mechanical/non-abrasive
Commercial purging compounds can help keep extrusion machinery running at optimum performance.
Mechanical/non-abrasive purging compounds are thermoplastic (non-chemical) blended compounds in polymer carrier systems with scrubbing granules. These granules soften on the outside, but remain solid on the inside so that the screw and barrel are scrubbed safely and thoroughly without wear. Mechanical/non-abrasive purging compounds are supplied ready-to-use by pouring the required amount directly into the machine.
Shuman Plastics’ Dyna-Purge is a mechanical/non-abrasive purging compound. Purging prior to a shutdown is recommended because it makes for easier start-up. Chemical purging compounds are active only for a specified period of time during the purging process, and become unstable when subjected to inconsistent heat and extended residence in the barrel or when used beyond their shelf life. Consequently, all chemical residues should be removed before shutdown for the protection of the equipment. The same is true for mechanical abrasives. If left in the barrel, these purging compounds may freeze, which can cause damage to the screw on start-up. Mechanical non-abrasive purging compounds do not degrade, and can be left in the barrel during shutdown to help ensure faster, easier start-up.
Commercial purging compounds, including Dyna-Purge, were introduced to the market more than 20 years ago. Despite two decades of performance and acceptance, many processors still use their own resins and regrinds as a home remedy in their efforts to purge economically. In fact, this is usually more expensive when bottom-line costs are computed. Regrind resin is not designed to clean processing equipment. It may appear to remove previous resins and colours, but it will not clean carbon deposits or negative flow areas.
Furthermore, the cost to purge is not just a comparison between the cost of a commercial purging compound weighed against in-house regrinds. All factors affecting productivity and operations must be considered (see Cost-to-Purge Worksheet).
Commercial purging compounds are available in a variety of formulations designed for specific processing equipment and temperatures. They work faster and clean more thoroughly than regrinds, which reduces machine downtime. More scrap is produced using in-house resins, contributing to a higher cost of waste disposal.
Taking Dyna-Purge as an example, there are no hidden costs associated with using thermoplastic purging compounds. Shuman Plastics recommends using 2.2 to 4.5kg per 2.5cm diameter of the screw (5 to 10 lbs. per diameter inch) to purge extrusion equipment.
Some colours, such as blue, and various types of resins are more difficult to purge, requiring the higher recommended quantity of purging compound. In addition, the L:D ratio may affect the amount needed for extrusion.
Typical instructions for using purging compounds, for example for Dyna-Purge, are:
* Select the appropriate grade formulation based on the process, running temperature and equipment.
* Maintaim running temperature and RPM of the machine (no adjustments are required).
* Empty the barrel and starve the screw.
* Measure one scoop at a time of purging compound and pour it into the empty hopper or side port.
* Flush out purging compound with the next material.
Other factors can contribute to the efficiency and effectiveness of purging such as the viscosity of the resident resin and the viscosity of the following resin, the size of the processing equipment, and the age and condition of the machine.
Quality practices also play a role. For example, these include whether there is a Standard Operating Procedure for purging in operation. Other issues include whether there is regular machine maintenance or purging is done only when time permits, or during an emergency.
Although the skill levels of operators may vary, a Standard Operating Procedure can help ensure uniformity of purging procedures among operators to achieve better, more consistent results.
Calculating the actual cost to purge must take into account a comparison of the cost of the purging compound, the cost of the carrier resin, and the amount of time for pre-purge, purge and post-purge.
Using purging compounds is less expensive because of the significant time savings and reduced scrap. Comparisons among different purging compounds typically favour the pre-blended ready-to-use mechanical brands (see Cost-to-Purge Worksheet).
For the plastics compounder, breaking down the machine and cleaning it thoroughly, is a time-honoured and acceptable way to prepare for changeovers or handle routine maintenance. With today’s increasing pressures to do more with less, operators do not always have that luxury. Commercial purging compounders, combined with the operator’s experience and skill, can help keep extrusion machinery running at optimum performance and give compounders a competitive edge.