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Brentwood Plastics blog

Joel Longstreth

Recent Posts

Plastic Shortages

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:37 PM

Part of Harvey's aftermath will be a shortage of plastics.  The general public cannot see it yet.  Many plastic processors and especially their customers are in denial.  Many large processors have shut down and sent their employees home.  For us old timers, recent events conjure up shortages of 1973 - 1974, 1998 and 2005.

 

 

 

The irony is that black plastic trash bags are badly needed in Houston now.  

The following is a recap of causes and outcomes of the previous shortages.

First, let's review the definition of a shortage.  A shortage is simply not enough of a commodity available at the price the market wants to pay.  Simultaneous to the oil embargo, there was a shortage of beef.  Vegetarians were not particularly concerned.

 

 

 

                                                  1973 - 1974


The plastic industry was a teenager. 6 years earlier, Dustin Hoffman's character Benjamin Braddock got the famous career advice -  plastics !   Resin was made either by chemical companies who were not basic in feedstocks or by a few petrochemical companies.  The chemical companies bought ethylene and propylene on the "spot" market.  When the oil embargo hit and monomers were in short supply, guess who got first option on ethylene and propylene monomer?

Plastic processors went on allocation based on historical purchases.  List price for polyethylene was in the 15 cent per pound range.  When Nixon instituted wage and price controls, people got creative.  Suddenly there was a plethora of material available in the 50 to 60 cent range.  It was labelled "off-spec".  One legacy of the big one:  no more "list" prices for resin.  There was resin, but not much for 15 cents a pound.  

During the roughly 16 months of the shortage, pricing was hour by hour.  The phrase "prevailing price at time of shipment" was added to the terms and conditions of sale.  Look closely in the fine print of an old plastic processor 's terms and conditions and you will probably see it.  

The shortage pricing collapsed in a matter of days.  Many plastic manufacturers reinvested their windfall profits in more capital equipment thinking the party would go on.  Instead, it lead to a glut of overcapacity.

1988

was short lived.   Processors on allocation quietly exported their excess resin to maintain their allocation. The resin companies figured out they were better off dividing the fishes and loaves among their smaller customers for higher margin than unloading in bulk to large customers at rock bottom prices.  Ever since, credit managers have had more sway.

2005

was the aftermath of Katrina and Rita, often referred to as "Katrita".  Natural gas spiked to an all-time high of $ 15.  Search volume for "price of plastic" also spiked.  Buyers who were not around for 1973 / 74 simply could not believe the price for a cheap commodity could go up that fast.  The lasting effect of Katrita was agreement upon the CDI as a basis for price adjustment.  The other lasting effect has been discipline.  There was major bloodletting at the resin companies in 2006.  Ever since, the resin producers have shown remarkable discipline. Now it's no forecast, no resin.  They no longer just make resin for it's own sake. 

 

Skip ahead to present day.  The initial shock of Harvey has worn off.  Now customers want to know when they will get resin and when.  What is reminiscent about 1988 is smaller processors are getting better access to resin than large volume processors.  Smaller processors defined as less than roughly 25,000,000 pound per year usage have been relegated to buying through prime distributors.  The large volume users are calling distributors with orders for multiple railcars.  They are perplexed when their orders are respectfully declined due to overriding concerns about keeping long-term smaller customers stocked with material.  Several large plants have simply sent their people home.

There are three components to producing resin - monomer, polymerization and transport.  The monomer and polymerization bits are coming back quickly.  The transport part is the crux of the equation.  There is an embargo on rail traffic to most of Houston.  Anyone who has dealt with railroads knows they are not going to put equipment on tracks until there is at least 105% certainty that the tracks are intact. 

Plastic processors simply do not know if they will get resin, when, how much or what the replacement cost will be.
Many are reluctant to snap up resin because they are either in denial or they still remember getting burned back in October of 2008 when resin prices cratered 30% in a few days.  
The "prevailing price" lingo won't fly today.  The good news is there is plenty of capacity ready to fill the void.  If past is prologue, the Harvey shortage will end with a whimper.

Harvey's aftermath is a slow-motion catastrophe.  Volume buyers of finished product are in denial.  Behind the scenes, volume processors have resigned themselves to being out of some grades and shut down by November. The conversations between WalMart buyers and their suppliers are going to be interesting.  

Processors and their customers who eagerly anticipate running reverse auctions when 18 billion pounds of capacity comes on stream are going to be disappointed.  Their is plenty of worldwide demand to take up the slack and resin companies are disciplined about forecasting and scheduling.

Question: If polyethylene needs to be rationed, what items should be priority?

Who should decide?

 

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Topics: harvey plastic, plastic shortage, price for plastic

LLDPE Linear Low Density Polyethylene varieties

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:33 PM

As with all polymers Linear Low Density Polyethylene LLDPE has a tremendous variation within the species.
This article explains the differences in context of the history and evolution of Linear Low Density PE.

Think of the differences between the grades like the difference in gasoline choices:

Butene    =   Economy

Hexene   =    Mid grade

Premium  =    Octene

These refer to the types of comonomer married up with the ethylene monomer to make linear low density polyethylene.

A quick history lesson might help.

Until the late 1970's, " linear" polyethylene was verbal shorthand for milk jug high density polyethylene HDPE.  It was nicknamed " linear " because it had very little short chain, or amorphous, branching.  The shape of the molecules was more like spaghetti before cooking vis a vis after cooking.

When Carbide shook the plastic world with the unveiling of their Unipol gas phase linear polyethylene in 1978, there was a lacuna, or " gap " in polyethylene language.  PE which was made in densities under 0.930 is by definition LOW density LDPE polyethylene.  To distinguish this new Low Density Polyethylene LDPE from conventional LDPE, it was dubbed LINEAR low density polyethylene or LLDPE for short.

Dow had a different approach with their " solution " phase polymerization process.  This mimicked the old DuPont Canada SCLAIR LLDPE resin which was the true forerunner of all Linear Low resins.

Carbide opted for the cheaper butene and Dow went top shelf with octene.  In the 80's, Dow was easier to process ( less susceptible to melt fracture ) and had better physical properties than the butene gas phase.  As a side note, Carbide tried for several years unsuccessfully to induce extruders to take the resin in the form of a powder ( think laundry detergent consistency ) and pass along the savings of pelletization.  Dow provided old fashioned pellets.

In the 90's, Mobil tried to bridge the gap with hexene which is less expensive than octene and more expensive than butene.  They made LDPE resins on Unipol style reactors.  They chased Octene with  " super " hexene which has always been " not exactly " octene.  The solution phase process allows more versatility and faster changeovers than Unipol.  

Skip ahead to today.  Butene - 1 is the only LLDPE film resin which is sold as a commodity on the London exchange.  It is cheap and weak.  Nova purchased the DuPont Canada PE resin works a few years ago.  Nova offers both butene and octene LLDPE.  "Super" hexene is still around.  Lower cost Unipol resin plants have sprung up all over the planet.  Nova just announced an expansion of another billion pounds of butene capacity.

It's kind of amusing to look back at the predictions of the late 70's with the benefit of hindsight.  Everybody thought LLDPE would make LDPE obsolete like TV was going to be the nemesis of radio.

Blends of LDPE and LLDPE deliver some interesting properties.  

When specifying Linear Low LLDPE, be specific about which kind of LLDPE you want and whether you want it 100% or blended with one of the myriad varieties of conventional LDPE.

 

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Topics: Linear Low Density Polyethylene, LLDPE

High Density HMWDPE Conundrum

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:33 PM

The acronyms HMWHDPE and  UHMWHDPE are confusing.  This discussion breaks down high molecular weight jargon.

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Starting with the MW bit -  MW is short for molecular weight.  MWD, or molecular weight distribution is the full name.  Accoring to Handbook of Polyethylene by Andrew Peacock:

     " The size of a polyethylene molecule is normally described in terms of its molecular weight.  All polyethylene resins consist of a mixture of molecules with a range of molecular weights.. The average molecular weight and the distribution of chain lengths comprising a polyethylene resin profoundly affect is ( sic ) properties.  The molecular weights of molecules found in commercial resins may range from a few hundred up to 10 million... Often it is found that those molecules making up the higher molecular weight fractions also display the lowest levels of branching. "

Without getting deep into the five geeky ways to measure MWD, suffice to say that a high molecular weight resin is concentrated, very crystalline ( little short chain brancing ) and very dense. No surprize that by definition the density is high - high density ( HD ), or over .940 gm / cc.

So HMWHDPE = " High Molecular Weight High Density Polyethylene"

As you might expect, these resins are among the strongest polyethylenes pound for pound.  They are so viscous that the ASTM 1238 test for melt index had to be revised when the original Mitsui 7000F came along in the late 1970's.  Melt index is a measure of viscosity.  The test method consists of a cylindrical specimen in basically a heated can with a weight and a hole at the bottom.  The number of grams which come out of the hole in ten minutes is called the melt index.  This provides a crude predictor of the resin's personality.  Garden variety LDPE resins are about 2 grams or the verbal shorthand " 2 melt".   Mitsui 7000 F, American Hoechst GM9255F2 and Conoco / Dupont 5000 had values of + - 0.05.  So the HMW film resins are now tested with a " high load melt index", or "HLMI" which simply means higher weight to get a more meaningful sample.  Some prefer to make it sound more daunting by saying  "HLMIHMWDPE."  The most cotidien examples are single use grocery bags and star- seal trash bags.

 

Did you know ?  If there is not adequate haul-off speed, thicker HMWHD films will be weaker.  Why ?
the strength is a function of how well the polymer is "knitted" in the transverse direction ( TD ).  Here's how it works:  HMHD is made with a "stalk" or "wine glass" vis-avis "in the pocket" in LDPE.

 

 When the elastic energy dissipates, the bubble is created.  The tear strength and is a function of how fast the melt is oriented in the TD.  Simply slowing the line speed will create weaker, "splitty" film.

UHMWHDPE as you might guess is an even higher protein version with molecular weights starting around 2,000,000.  Those are long chains.  That said, most grades are in the .928 to .941 range which fall into the category of medium density polyethylene ( MDPE ). You can't make blown film out of it.  It has to be cast, or made with a slot die.  It is very stiff and slippery to the point of having a weird self-lubricating effect.  This trait makes it a popular choice for conveyor belts. I recently had a partial knee replacement.  Instead of a meniscus, I have a stainless steel end of my tibia moving against an insert of HMWHD in my fibula.  ( i have an image, but it's not for the faint of heart ).  There are lots of uses - the most popular is pressure-sensitive tape commonly referred to as "poor man's teflon." 

For the basics of PE, click here.

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Topics: HDPE, HDPE film resin, HDPE resin, UHMWHDPE, HMWHDPE

Carbon in PE film

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:32 PM

Carbon specs in polyethylene LDPE film are inevitable.  I had to explain this to yet another prospective customer who has a zero tolerance for carbon in film.

When simple hydrocarbons are exposed to prolonged heat, they become carbon when overcooked.  PE resin which gets hung up in the extruder eventually becomes carbon.  From time to time, these specs break loose and end up in the PE film.  It is impossible to see all of them without 100% manual inspection which is not practical at linespeeds of hundreds of feet per minute.

Carbon will break loose more often in a "job shop" because the viscosity of the resins changes frequently.

These carbon specs are inert, they are not impurities and much less harmful than any PVC. 

Just the same, perception trumps reality especially in clean room and medical where every square inch of film is inspected stiing still.  Rather than set one roll of film aside, the tendency is to throw the baby out with the bathwater and reject the entire run.

In 50 years, we haven't figured out how to prevent carbon in LDPE film.  The most practical solution is to just set the rolls with carbon aside. 

Over the last few weeks I noticed my car's gas mileage dropped.  Less than an hour after the discussion about carbon, the idiot light came on.  Turns out my car needed a serious accumulated carbon buildup purge.

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Topics: carbon in film

PE Resin in the Age of Madmen

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:30 PM

While spring cleaning, we found a cache of 1960's era letters from Union Carbide.  

       

 

 

wise-guys.jpg

The letters were from big shot execs in the mid-town Manhattan offices.  All were perfectly individually typed with no errors ( whiteout probably did not yet exist ).   While Don Draper was working on ads for mass marketing, the senior execs were incredibly creative by tying in first day of issue stamps to their new resins for the narrow nascent blown film industry.

Of course there were many things nostalgic and laughable - six cent stamps, new applications such as shrink film, juice packaging, frozen food packaging.  Recycling ?  Re-what ?  Linear Low Density was over a decade in the future.  In the First Man on the Moon issue, they bragged about their two billion pounds of capacity.  They went to great lengths to show literally how far their resin would stretch - to the moon and back many times. There is at least 35 billion pounds of PE capacity coming on stream in the US in the next few years.    

In the late 50's the commercial feasibility of blown film was uncertain.  Today there are over 27,000 known blown film shops.

Reminds me of when our founder used to line up his three martini lunches on successive days when he worked for USI Chemicals.

 

How times have changed.  

Enjoy the gallery.  ( Click the enlarge.jpg below the slide show for full screen )  Who knows ?  Maybe the collection will appraise at $ 5 at the Antiques Road Show in the year 2100.

 

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Topics: LDPE resins

Polyethylene Resin Factors of Production

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:29 PM

 

The price for polyethylene depends mainly on the factors of feedstock, or monomer, pricing and exchange rate. 

Exchange rate has a direct bearing on domestic prices because it affects export resin sales.  If the dollar is weak, dollar denominated resin becomes more attractive for export sales.  US processors simply have to pay the same price as export.

Feedstocks for so called "petroleum plastic" or "petroleum based plastics" are either oil or natural gas.  In North America, we derive resin from natural gas with the exception of polypropylene ( PP ).  Polypropylene is a by-product of the refining process; approximately 80% of North American PP is derived from oil. In the middle east and other places, they make resin out of naptha - the creme de la creme of a barrel of oil.  Naptha cannot be refined into gasoline or motor oil.

The US becomes the really low cost producer when natural gas is low and barrel oil price is high.  This is referred to as "feedstock imbalance."

Ever since Rita and Katrina combined to push natural gas prices to $15 / MCF, resin producers, processors and their customers have struggled to find a mutually agreeable benchmarking index.  While CDI ( http://www.chemicaldata.com/ ) is referred to most often, CDI has been challenged by resin producers often.

Here are a few complicating factors:

Lead time  Commodity resin manufacturers do not carry much inventory.  To have resin in inventory, processors must forecast 6 months in advance plus allow 5 weeks in some cases for a car of resin due to the X factor of the railroads.  When customers hear the price of resin has dropped, they want an immediate discount despite the higher historical price of inventory on hand.

Specialty performance grades do not move in lockstep with commodity prices.  Buyers are myopic about pricing and value of performance plastics if they only look at the latest CDI report.

Cost of goods sold - Steadily increasing higher resin costs put the squeeze on COGS & operating capital requirements.  Processors limited to only the increase of raw material costs find their cost of goods sold expressed as a percentage of sales ratcheting up at a frightening rate.  This is further exacerbated by inability to pass along other rising costs of doing business such as freight, power and health care.  It gets worse.  The same scrap rate with resin at triple the cost of 15 years ago erodes margins even further.

So what's the solution ?
One sure fire way to eliminate arguments over the price for polyethylene is to "toll" the resin.  This is a common practice.  The customer purchases the resin; the processor charges a lower rate since his capital is not employed.   Resin cars weigh 200,000 pounds so the math works out perfectly.  One car equals five truckloads of finished product.

Popular three year deals with quarterly adjustments do not benefit both parties as much as monthly adjustments.  Monthly adjustments allow optimizing of inventory levels to take advantage of the fluctuation of the price of PE resins.

Rather than focusing on the MSI, weight per part or price per pound, utilizing resins which are stronger gauge for gauge than commodity plastics results in a higher price per pound and lower price per part.  Specific to heat shrink films, reducing the amount of TD shrink to a consistent amount builds up to huge numbers.  Each percent of TD width is an equivalent % of savings.  Invoicing by net weight rather than gross weight saves money too.

Here is a link to every conversion factor you'll ever need for polyethylene films.  Try a few examples to see how fast a small reduction adds up:

http://www.brentwoodplastics.com/handy_math.html

 

LDPE film price

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Topics: petroleum plastic, PE resin

Odor and Taste / Leachables and Extractables in Plastics

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:25 PM

 

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Leachables & extractables / odor & taste transfer in packaging have been a perennial source of controversy and product rejections.  Nature's penchant for equilibrium results in migration of substances from plastic packaging into the product.

If glass was a new invention, it would be difficult to get FDA approval due to the elements which leach from it.  It's cliche but true - anything in quantity is poison.

The ramifications of leaching and taste transfer can range from annoying and inocuous to toxic.  The metallic taste in tap water resuls from rusting ductile iron pipe.  A faint plastic taste will eventually show up in old bottled water.  Harmless but annoying.  There is no telling what contaminants can enter the recycling stream in post-consumer reprocessed plastic.  For this reason, reprocessed plastic is not an option for food or pharmaceutical packaging.  There is one exception - polyethylene terephthalate ( PET #1 ) which is re-polymerized vis-a-vis reprocessed, 

Commodity plastics such as polyethylene ( PE ), polypropylene (PP) and polystyrene ( PS ) are popular choices for food grade packaging because they are so inert.  For reasons still unknown, some polymers transfer taste to specific products.  For example, anyone who has made institutional milk bags knows there is zero tolerance for EVA.  The bouquet of EVA ( best described as apple vinegar ) transfers to milk.  

The subjective zone often results in vicious disputes.  Years ago, a major manufacturer of cereal detected an oxidized odor in the film yet there was no transfer to the product and there were no consumer complaints.  The film supplier had to make sandwiches out of the returned film because the cereal manufacturer refused to pay the invoice.

After 40 years and millions of pounds of ice bag film, we no longer make film for ice bags due to subjective, specious odor and taste complaints. 

Of course, very real leaching can ruin entire lot of product by the presence of only trace amounts.  Many a lot of circuit boards has been ruined by a few hundred parts per million of slip or silicone. Clean room packaging has zero tolerance for slip and silicone.

The threshold of parts per million has very serious legal implications, mainly about compliance with regulations. California prop 65 is not going away.  The scope is expanding indefinitely.  

Extractables encompass everything from the monomer itself to residual catalysts and additives.  So let's break it down:

monomers  Plastic is made from simple hydrocarbons.  With the exception of PVC, these feedstocks have been shown to be inert and harmless.  Old fashioned HDPE is still a popular choice for distilled water.

catalysts are necessary to facilitate a reaction to create the polymer chains.  The catalyst is either transformed or used up.  Remember the hysteria over BPA ?  Turns out it might have been overblown.  
Like it or not, the catalyst BPA is here to stay.  If BPA is an indisputable carcinogen, we should discontinue the use of ubiquitous 5 gallon polycarbonate carboys today.

Additives is a big subcategory encompassing antioxidants, stabilizers, antiblock, slip and pigments.   Additives each have a specific job to do.  Without antioxidants, plastics would have an odor like the smoke from a candle which was just extinguished.  Consumers would return any food packaged in an "antioxidant free" package.  Most resin antioxidants are tocopherols commonly known as vitamin E.  Only PVC has phthalates for stabilization.  

Antiblock is diatomaceous earth.  It is so inert it is used to encapsulate nitroglycerin to make dynamite.

Slip is used to make plastic slippery as the name implies.  Most slip additives anymore are pure enough that they can be Kosher certified.  

Most US made pigments are HMF, or "heavy metal free" if the end use is food packaging or anything medical.   The yellow does not contain lead and the orange no longer contains molybdenum. But most consumers prefer to eagerly expose themselves daily to dermal exposure to levels of lead which are in direct violation of CA prop 65.  

Quantifying leachables and extractables is done according to ASTM WK43975.  The extraction test is done in two solvents.  The extractables must fall below specific threshold amounts to be considered FDA approved.  

Of course, what is difficult to capture is goodwil and good faith.  If somebody is looking for an excuse to not pay their bill, odor and taste is a handy excuse.  As many injection molders found out ( some were put out of business ), the test method of CA prop 65 was modified to obtain the desired lead threshold results.  Whether or not the thresholds posed a realistic health hazard was irrelevant.  

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Topics: leachables & extractables, toxic plastic

FDA Approved Packaging - what does it mean ?

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:23 PM

Everybody knows the final arbiter of prolonged and direct food contact is the FDA food additives act of 1958 sections 404 and 505 section 177.15 20, 175:30, right ?

So why do we need other standards such as USDA, CFIA, AIB or Kosher approval ?

The truth is FDA approved packaging depends on your definition of FDA approved.  A little history lesson here:  There are two distribution channels for polyethylene resin - "prime" defined as sold direct through major resin producers and "off grade" sold at a lower price through what is known as brokers.  Prior to the Reagan administration, only prime resins had FDA certification and traceability.  In the 80's the rules changed.  The burden of FDA approval was shifted to the private sector away from the FDA by requiring a chain of certifications from the producer to the end user.  The unintended consequence - unscrupulous resellers now certify off grade simply by writing a letter.  Voila !   The end user has an FDA letter to cover. 

Its worse than you thought.  I have confronted FDA officials at conferences and they simply shrug and say they have higher priorities. 

Other than USDA certification for bio-based plastics, there is no such thing as USDA approved poly film.  Caveat emptor any plastic film supplier who purports to have USDA approved plastic film.


CFIA approval is impractical.  The film extruder must submit each combination of resins to the Canadian government and hope for approval.  Even Nova has not been able to achieve CFIA approval.

While AIB is stringent, the most demanding food grade packaging is Kosher approved.   Kosher approval requires due diligence of raw materials and practices by an individual. 

Brentwood Plastics does not publish Kosher approval letters for fear of plagiarism.

Based on our experience, Kosher approval is the gold standard.

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Topics: FDA approved packaging

Polyethylene Density

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:21 PM

The properties of polyethylene are most affected by the density of polyethylene.

Without going into the vagaries of molecular weights and molecular weight distribution, there are 2 key polyethylene properties which are a function of density.  They are secant modulus ( a fancy word for stiffness or softness ) and heat resistance.  The lower the density, polyethylene is softer.  The higher the density, polyethylene is stiffer.

Density is expressed as grams per cubic centimeter.  Polyethylene has inexact demarcations between high density ( HDPE ) over .940, medium density ( MDPE ) .939 to .927, low density     ( LDPE ) .926 to .915, very low density ( VLDPE ) .914 to .905 and ultra low density ( ULDPE ) .890 to .904.  New metallocenes are emerging all the way down to .860.  They are so new they don't have a name yet.

Polyethylene has an advantage over PVC from what is known as "yield" or area of plastic sheet derived from a pound of resin.  PVC has a density of around 1.25 gm/cc.

To relate to these properties, here are a few quick examples from everyday life:

milk crates
made from an extreme HDPE of at least .962, a milk crate is stiff and has a high melting point.

milk jugs
.957 HDPE.  Here's a fun fact:  milk bottle resin was nicknamed "linear polyethylene" in the olden days because the molecules are lined up in a linear fashion making this the original linear PE.  The molecular structure of Linear Low Density or LLDPE, is similar, hence the verbal shorthand "linear low" vis a vis the old linear which is high density ( HDPE ).

motor oil bottles
.952 a little softer and squeezable than milk jugs

dry cleaner bags
made from a .915 to .918 LDPE, dry cleaner bags are soft and pliable with a low melting point

bread bags
.923 is the most popular choice for a middle of the road PE film

soft goods overwrap
.927 to .933 density MDPE is the perennial favorite for packaging rolls of paper towels.  This film must be stiffer to process on high speed wrapping equipment.

Metallocene mPE in different density ranges exhibits these same traits.  Metallocene is taking polyethylene where no polyethylene has gone before, but that's another story.

For geeky arcane, in-depth background, visit

http://www.brentwoodplastics.com/polyethylene.html

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Topics: polyethylene density

What is Regular Poly Film ? is an oversimplification

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:21 PM

Asking for " regular poly" film is like asking for a regular car, beer, soda, tape or wine. 

The variation within the species of polyethylene film resins has evolved because different PE resins are made to do different jobs.  Just as one would not use a subcompact car to do the same job as a passenger van, it does not make sense to use the same PE resin made for dry cleaner bags to package 50 pounds of rock salt. 

We do have a middle of the road general purpose clear LDPE sheet film called GPC http://www.brentwoodplastics.com/data_sheet_gpc.pdf#zoom=100.  While it is warranted to be only a simple low cost general purpose plastic film, people continue to try to cut costs by using general purpose clear for applications which require specific properties. 

Here are just a few cases of ordering GP clear plastic films to cheap it out and why they ended badly:

Bread bags must have a very low coefficient of friction ( COF ) to load and release without jamming up.  General purpose clear is not a high slip / low COF poly film. 

Potato bags must be stronger than bread bags for obvious reasons.  The bailer bags which hold 10 or so potato bags must be very strong and low slip for stackability.

Ice bags and IQF frozen films must have EVA or metallocene for low temperature stability and strong seals.

Shipping sacks, like bailer bags, must be made from a more durable resin usually having a lower melt index known as a "fractional melt" for durability and must be low slip.  GP clear is not strong and the bags slide all over the place.

Lamination sealing layers must have a fast hot tack achieved only with the addition of EVA or metallocene.

Bank deposit bags must have zero slip or the pressure sensitive tape will not adhere to creat a tamper evident seal.

Last week we had two inquiries for "regular poly" to be used in prolonged and direct contact with human skin in medical devices.  We had to explain that different rules apply for medical applications.

There is no such thing as regular poly.  It is best to tell your PE film supplier what you are doing with the film, then continually test as you scale up to determine suitability for any end use.

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Topics: poly film

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