Address
phone
directions
We blog only about timely and relevant topics.  The software does not allow rearranging posts, so they are chronological.  You can browse by topic or keywords by scrolling down on the right side.

Brentwood Plastics blog

Joel Longstreth

Recent Posts

Why Recycled Plastic Content is not Always Practical

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:20 PM

"Recycled Content" must score well in focus groups.  What else could explain why we are getting more requests for recycled content than ever ? 

 The economics of recycling is an entirely separate discussion.  Here are a few reasons why it is not always practical to recycle plastics.

" ( Post-consumer resins are) very important to some brand owners"   
-  Pedro Morales, KW Plastics

 

2ndplantbottle.jpg 

Problem:  With very few exeptions, recycled content compromises the properties of the virgin resin.  This has many ramifications.  Taking the exception first, let's look at polyethylene terephthalate a/k/a PETE #1.  It is not melted down and mixed back in with the virgin resin.  Instead, it is repolymerized.  The polymer is broken down into pure monomer and water and reassembled into pure polymer.  PETE is the only recycled resin approved for medical devices.  Not so fun fact:  the general public chooses to recycle only 1 in 3 PET bottles.

" We need ( post-consumer) polyethylene to be looked at like recycled PET is...  Recycled PET  is sold at a premium ( to virgin PET ).  ( Post-consumer) polyethylene needs that same kind of attention." 
- John  Picciuto, president of Western Plastics Association

For this to happen, post-consumer PE ( #2  & # 4 ) would have to attain the same FDA-approved status that PETE has.  

Really truly recycled plastic is picked up curbside, sorted, reground, repelletized and extruded again.  Internally generated scrap which is recycled internally does not fit the definition, but nobody cares or checks up.

earhaware.jpgearhaware2.jpg

At every step there is a chance for contamination.  Cross contamination with other polymers is one of the top issues for recyclers.  If the recycler is fortunate enough to have a batch of just one polymer, that's not even half the battle.   There are variations on the theme of each resin.  So contamination from the same polymer can compromise the final product.  With each heat history, the performance of the polymer degrades due to dissipation of the anti-oxidant.  Recycling makes the public feel good.  In reality it is downcycling to a less critical application.

Medical and Clean Room Packaging

Would anyone in their right mind want to use a medical device such as a syringe which might contain even trace amounts of toxins ?   We have made film for ostomy bags ( prolonged direct dermal contact ) for over 15 years. It's tough enough just to get prime virgin resin approved.  The resin has been put through four biotoxicity tests. Only somebody who wants to get sued would consider using partially recycled content.  Same goes for surgical drapes which come in brief contact with surgical instruments.

The same hospital that discards a blood presure cuff ( after charging the patient $25 ) for fear of a MRSA lawsuit will recycle / sterilize sharps because it makes economic sense.

disposable blood pressure cuff

Clean room packaging has a very low parts per million threshold for many chemicals.  Introducing the wild card of recycled content would risk recall of an entire shipment and loss of a customer, not to mention getting charged back for having to repackage.

dreamstime_s_17056637.jpgdreamstime_s_22175857.jpgdreamstimesmall_12386776.jpg

 

Food and Water Packaging

PETE is also the only recycled resin approved for prolonged and direct food contact by the FDA.  Same logic applies to food.  Would you feel comfortable with your food being packaged in a container which might contain toxic chemicals picked up as the scrap is transported and processed  ?   Plastics already get enough of a bad rap due to misperceptions and misinformation.


BPA free is an effective greenwash marketing tactic.  Food packaging also gets scrutinized for what is known as leachables and extractables to be sure undesirable flavors are not migrating into food.

cuisinart.jpg images.jpgdreamstime_s_29972885.jpg

 

Deposit Slip and Coin Packaging

deposit_bag.jpgfedcoin.jpg2nddeposit.jpg

All bags in this category must have a tamper-evident immediate bond.  The three things which prevent tape from sticking are moisture, dirt and grease.  As such, they have a zero tolerance for slip, or erucamides which are commonly added to make bags open easily.  Adding in recycled content which may have trace amounts of slip could prevent the tamper evident tape from sticking.  The center image is fifty pounds of loose coins.  It is very difficult to qualify film made from prime first quality resin.  The bags are put through multiple drop tests.  If the seals fail, the film is always blamed, not the bag maker.  You guessed it - recycled resin would make the bags weaker and possibly keep the tape from sticking.  

There are plenty of other applications, but you get the idea.  The common thread - is it prudent to risk so much just to appease a great idea from the marketing department ?  

 

 

 

Read More

Topics: recycling, recycled content, recycled plastics

PE Film Make / Buy Decision

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:17 PM

It's cliche but true - when milk is cheap, why buy a cow ?  Peter Drucker said it is better to integrate upstream than downstream.  The case for vertical integration play involves payback analysis and other factors.  Henry Ford made his own power mainly because he was fed up with dirty intermittent power.  I can relate.

The most common fallacy of vertically integrated PE film supply is not treating it as a stand-alone P & L.  

secondmoneyarrows.jpg

Many companies opt to buy film even though they consume enough film to feed a grass roots film plant.
Procter and Gamble Clopay have had a symbiotic relationship for generations.  When P & G puts up a diaper operation, a Clopay embossed film plant will pop up in close proximity.  It's only one item.  

Custom flexible packaging has more moving parts.  There are good reasons to buy PE film on the outside:
1.  Lead time     Using multiple extruders increases the likelyhood of finding a line which needs work.  The New York tri-state area is the best example in the US.

2.  Painless rejection   Rejecting film which comes from an outside source does not generate the acrimony resulting from an internal rejection.  Gotta keep the prima donna pressmen happy, right ?  Finding another film source is easy.  Finding a reliable pressman is not.  If you don't reject film outright, specious claims are a time-tested means to shaving a few cents off raw matierial costs.  The extruder would rather take a discount than see the film show up on his dock.

3.  Cash flow and turns   Most bag makers do not understand the concept of borrowing to pay invoices timely.   Line of credit ?   What's that ?   It's simpler to buy from multiple sources and string out your accounts payable.  If you do hit your credit limit, buy from a different extruder.  

Buying resin is more complex.  
You have to:
forecast 90 days rolling
wait sometimes five weeks for the railcar to show up
pay bills timely
provide quarterly financial statements to the resin companies

If you're on the wrong side of the market, every penny you're off =  $ 2,000.   Film prices drop shortly after CDI comes out.  Whatever is in the silos gets devalued.  Why bother ?   It's much less risky to order film for each job.

4.  Lowest cost   Overcapacity in blown film is a time-honored tradition.  Don't just keep your supplier honest.  Constant reverse auctions give new definition to keeping a supplier honest.

One of our successful alumni - Dave Frecka, founder of Next Generation Films - is betting big on yet another expansion literally the size of two homesteads.  He's betting that his customers will not make their own film.

Flexible packaging converters see making film as much simpler than their complicated processes which involve inks, plates, solvent recovery, adhesives, people, bag and pouch making.  They visit a blown film plant, see an operator sitting down reading a book or taking a smoke break.  The operator is sitting down because he's exhausted from all hell breaking loose over the last two hours.

In theory making blown film is a simple, continuous process.  If it was really difficult and complex, there would not be over 27,000 known blown film shops on the planet. The truth is making blown film is an art despite what equipment manufacturers proffer as "turn-key" lines.  There is a learning curve. 

Let's look at how seemed to be a good idea at the time that led to a salvage play.

The same schedulers who won't schedule a print job until the plates and film are both present hate to wait for film.  The reason the printer has to wait is that a properly run film backlog prioritizes minimal scrap. When the backlog is set up on a first-in-first-out basis or disrupted by the printing plant manager who succumbs to an ultimatum from the cutomer who has threatened to cancel ( sticking the converter with the cost of the film and plates ), excessive transition scrap is the result.   Scrap factors which are not captured in the in the justification for going vertical are transition scrap, internally rejected film, startup and shutdown scrap.  The boffins pick up on the higher than projected cost of goods sold first.  Until the day of accounting reckoning arrives, it's a myopic free-for-all.  Everybody feels good about percieved free film, controlling their destiny and not getting ripped off by their film supplier.

Of course, there are many successful vertically integrated operations.  If the end product has ample gross margin, allocation of the cost burden is moot.  I'm not making this up - many lucrative operations have an internal transfer cost of a penny over resin.   

A blown film operation is capital intensive with inherent high operating leverage.  It makes or loses money incrementally on either side of break-even.  When volume falls short of the break-even, the "prisoner's dilemma" follows.  Running at a loss is better than shutting the line down.  The penultimate desperate phase is scrambling for cheap work to maintain cash flow.  Over the years, I have been to many industrial funerals known as auctions.    We get notifications of liquidations every 6 weeks or so.  We hear from leasing companies who ask if we are interested in lines they have "carved out" of a converting operation.  When the line was first up and running, there was a party atmosphere - " whooopee !  free film !  on demand ! "

So if you are contemplating making your own film either financed or with a few extra millions of extra cash, our advice is to be sure you have:

1.  sales to feed the fixed cost beast
2.  lots working capital and a line of credit
3.  a strong plant manager
4.  commitment to a 24 / 7 operation

Read More

Topics: LDPE film, PEfilm

Plastic Film Thickness Variation

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:15 PM

While plastic film made by the blown film process can be controlled closely, there are limitations imposed by the interdependent factors of the process and plastic resin selection.

IMAG0153 resized 600

To understand the physics of the blown film process, think soap bubble blown vertically.  When the bubble starts out, the wall is thick and stable.  When it gets larger, the wall is thinner and starts shaking.  The relationship between the bubble size and the circular die, or aperture that the melt exits from, is a key factor called blow up ratio or BUR for short.  Gauge profile is easiest to control at low blowup ratios.  Problem: PE film made with a low blowup ratio can be weak and exhibit the dreaded straight line tear which results from too much orientation in the machine ( MD ) direction.  While the textbook happy spot is a blowup ratio of 2:1 ( bubble diameter = twice die diameter ), this is not always possible in the real world.  If scheduling realities dictate a higher blowup ratio, the operator must use tricks of the trade to achieve a flat, even plastic film.

The other component is resin selection.  Resins with higher viscosities or lower melt index, or "MI" for short, lend themselves to an even thickness profile. 

Of course, in the real world not every plastic film can be made from a very low preferably "fractional melt index" resin at a low blowup ratio.  Ironically the least critical blown film application - shrink film - is made with low melt index, low blowup ratio.  Anymore blown film plant managers are chefs who manage what winemakers call cuvees, or blends, of resins.

PE film with excessive variation is maddening when heat sealing and laminating.  "Baggy film" is a perennial complaint which will bounce a roll of film a country mile without hesitation.

There is a fundamental difference between point-to-point thickness variation and what is known in the converting industry as Yield or area derived from a specific weight.  Here are PE film conversion factors in both English and Metric units:

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

A good starting point for agreeing on thickness variation is the Flexible Packaging Association spec B 11.  Sorry, we can't link to it.  You have to buy a copy.

Over the years the capital equipment manufacturers have endeavored to make blown film lines which guarantee + - tight tolerances with non-adjustable features which take the operator variable out of the equation.  For now these luxury store bought turnkey lines are too rich for our blood. 

We can't help believe blown film is still an art and the operator should take responsibility for his workmanship. It is our tradition that every roll we make has the operator's ( or should we say artists ?) name on it.

Read More

Topics: blown film, pe film, LDPE film, blown film extrusion, plastic film properties, plastic film

PEVA film is not the only PVC substitute

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:14 PM

not PVC shower curtainPEVA materials are not the only PVC substitute film.

PEVA film is a popular substitute where PVC has been banned mainly because it is what is known as a "polar" molecule.  The properties of polyethylene film copolymer EVA also known as PEVA material most closely mimic the polar nature of PVC.  This makes "PEVA" the path of least resistance when substituting for PVC. 

PEVA shower curtains are a ubiquitous PEVA film success story.  It is interesting to note that the retail price of a PEVA shower curtain is about triple the cost of a PVC shower curtain.  The cost to manufacture is identical for both PVC shower curtains and PEVA shower curtains.  The claims of "Eco Friendly" and biodegradable are unabashed greenwashing claims know politely as "son of fibbing" or outright lies depending on who is defining the greenwashing sin.

Not all PEVA's are created equal.  PEVA is short for "Polyethylene Ethylene Vinyl Acetate" which is a copolymer of ethylene and vinyl acetate. The copolymer is made by the resin producer in varying percentages, not added by the blown film manufacturer.  Therefore it is essential to specify the percentage of EVA copolymer in the PEVA material.

New metallocene catalyst polyethylene films emulate the "hand" of calendared PVC.  Metallocenes have proven to be very clean in biotoxicity tests in medical applications requiring prolonged and direct skin contact.  While RF welding metallocene requires a learning curve and a modified "buffer", metallocenes are readily heat sealable.  Custom shapes can be achieved by a heated seal which is a heated die rule.

An additional side benefit to both PEVA and metallocenes used where PVC is banned is they are considered "burnable" by European standards. 

describe the image

A new category of polymers which we'll call thermoplastic olefins, or TPO's for short open up some exciting possibitlies such as digital printable custom shower curtains and wallcoverings

Read More

Topics: PEVA, PEVA material, PEVA shower curtains

Thicker plastic film is not always better

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:13 PM

The shortest route to a good sustainability scorecard is source reduction.

New resins get the job done using less wall thickness in packaging applications.  There is a definite trend towards using less, albeit slowly. 

So what is holding back adoption of thinner packaging even after the efficacy of a thinner package has been proven through drop tests and shipping tests ?

Based on my own observations and experience, it is usually one of two fear factors:

Consumer will percieve the product as being cheaped out if the packaging is thinner.  Marketing assumes this is the case without focus grouping or test marketing.  For example, a very green manufacturer of organic granola who hates plastic got cold feet about using a thinner sealant layer.  When you get down to brass tacks, it's not worth taking a chance at point of sale. 

It's also not worth taking the chance that the packaging will fail during shipment.  Seriously, what is your motivation to sponsor using less packaging if it fails ?  If it fails you get blamed and lose your job. 

We recently reduced the thickness of a frozen food bag to 3.5 mils from 5 mils.  When we asked them why they were being so conservative and not cutting the gauge to 2.5 mils, they said they were happy enough and were not interested in further reductions due to the aforementioned fear factors.

If a resin is a bad actor at 3 mils it will not work at 5 mils either.  If the right resin is matched to the application, less is needed.  It's that simple.  Many of these resins cost more per pound than a general purpose resin.  If the extruder cannot pass along the cost to the end user, what is the incentive to inventory the upmarket resin ?

Sadly, the custom of selling film by the pound impedes progress.  Even after showing the math on how much less the unit cost would be through more expensive thinner film, buyers often do not agree because they are inured to price per pound.  Most extruders live and die by pounds shipped, so there is not much motivation to push downgauging or lightweighting.

All parties would benefit from a more expensive plastic film per pound offset by gauge reduction.

Here is a link to make the calculating easy:

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

 

Read More

Topics: LDPE film, poly film, PE film packaging

EVA and PEVA - be specific

Posted by Joel Longstreth on Thu, Apr 25, 2019 @ 03:12 PM

EVA and PEVA are both acronyms for Ethylene Vinyl Acetate.  Somehow the P for polyethylene was added to create the acronym "PEVA."

To make EVA copolymer, Vinyl Acetate Monomer or "VAM" is copolymerized, or conjoined with Ethylene monomer to make Ethylene Vinyl Acetate. 

EVA copolymer is made in varying percentages from 2% EVA, 4% EVA, 6% EVA, 8 % EVA up to about 28 % EVA for blown film.  If you order simply "EVA" it is too broad and not specific enough.
The percentage of EVA is critical because the greater the EVA component, the lower the melting point.  This affects the EVA film performance properties.  If you are RF welding, the more EVA is needed for response to RF frequencies.  For low melt / total batch inclusion, the amount of EVA must be known to match with the desired melting point.  EVA is popular for solar photovoltaic pv cell encapsulation, yet EVA film suppliers do not specify the percent of EVA in the film for solar panel manufacturers.

When ordering EVA film, be sure to specify the amount of EVA for consistent performance.

Read More

Topics: EVA sheet solar, EVA film, solar panel manufacturers, PEVA film, PEVA, EVA film supplier

PE film tin canning

Posted by Joel Longstreth on Wed, Apr 24, 2019 @ 06:16 PM

polyethylene film tin canning
 
"Tin canning" describes the longitudinal ridges which often appear in low density LDPE polyethylene film - usually blown PE film.
 
For many applications of PE film, tin canning does not matter.  Heat shrink film is one example.  The ridges smooth out when the film shrinks.  Same goes for industrial box liners.  Not so for film which gets printed, laminated or coated.  These demanding processes require a perfectly smooth " lay flat" film.  Any film with a slight indication of tin canning ( usually by the pressman who taps at points across the roll looking for a slight marshmallow like surface ) gets rejected before it gets put on the press, laminator or coater.
 
Of course only the blown film manufacturers care about the causes of tin canning.  Customers just want flat PE film.  Here are some factors which can contribute to tin canning:
 
resin selection
a no slip / antiblock only film with a high COF will not "settle" after being wound up
 
thickness
thinner films will get stretched more on the way to the winder, exacerbating any imperfections in gauge profile
 
treatment
treated films with their higher surface energy tug at the interfaces of the layers on the roll
 
width
wider webs have more area across the web
 
While the main culprit is excessive winding tension which stretches the film and does not trap microscopic pockets of air in the roll, you might have to live with occasional tin canning if you call out a no slip, wide, treated PE film.
Read More

Topics: LDPE film, PE film tin canning, blown film extruder, tin canning

BHT in Polyethylene Film

Posted by Joel Longstreth on Wed, Apr 24, 2019 @ 06:15 PM

Customers continue to ask us for assurances that our PE films do not contain BHT.  The reason they ask is that BHT makes film printed white turn yellow.  When exposed to light, the yellow turns white again.

We just got another one of these inquiries.  To understand it chemically and to have it explained in 10 year old English, I asked our guru - Mr. Rudy Bourgeois of the M Holland company.

His response:

"BHT especially makes white print turn yellow due to the iron content in the white masterbatch which acts as an accelerant to the reaction described below:

BHT was used years ago as an A/O agent.  It has a low molecular weight and a relatively low melt point, which made it ideal for protecting PE resin during extrusion.  The downfall of this phenolic A/O is that it migrates and reacts with the lignins in paperboard and also with the exhaust gas from forklifts to form a compound called stilbene quinone.  This compound is crimson color in concentrated amounts and yellow in diulted amounts.  

It is a reversible reaction and will go clear again when placed in sunlight for a while."

So now we know.  Thanks, Rudy !

Read More

Topics: BHT, BHT in PE film, BHT free

Melt Fracture in PE film

Posted by Joel Longstreth on Wed, Apr 24, 2019 @ 06:13 PM

Melt fracture a/k/a "sharkskin" or "applesauce" occurs in LLDPE film.

melt fracture polyethylene film LDPE

To say that much has been written on the subject is an understatement.  Entire books and dissertations abut melt fracture have been written by polymer chemists a lot smarter than me.  Still there is not total agreement on the causes.  Personally, I have a hypothesis that it has something to do with susceptibility to degradation in the transition section of the screw.  

 

Going back to the early days of LLDPE  http://www.brentwoodplastics.com/blog/bid/131888/LLDPE-Linear-Low-Density-Polyethylene-varieties melt fracture was just expected in butene LLD but not Octene.  Carbide advocated a return to shorter L/D ratios for shorter residence time.  This and granular resin never really took off.

No matter the cause, melt fracture results in a very irregular scaly texture to the film.  In most cases, this is considered an undesirable quality because it detracts from the cosmetics.  In a few cases such as forearm protectors it is considered a plus but i don't know why.

Read More

Topics: LLDPE melt fracture

Visqueen  Construction Film

Posted by Joel Longstreth on Wed, Apr 24, 2019 @ 06:11 PM

Visqueen is another word for construction and agriculture, or "C & A" film.  Visqueen, like "Frigidaire" and "Kleenex" is an example of what linguists call a secondary meaning or what happens when a brand becomes so commonplace that it is substituted for the original meaning.

 

 

Click here for a history.

Visqueen is used for non-critical applications not just on construction sites and farms.  It is the lowest end of the blown polyethylene film market. Any PE resin which can be extruded into blown film will do.  Cheating on weights and measures is commonplace.  Full gauge and width is an exception and nobody cares.

Visqueen is often used to make makeshift greenhouses, but it will not last long due to degradation from UV rays.

It is commonly sold in 100 foot lengths in widths from 10 feet and wider in natural and black.

 

We get lots of inquiries for Visqueen because it is polyethylene film.  We don't make it.  We're set up for large
"mill" rolls.  If you are looking for Visqueen / C & A film, here are links to some US manufacturers:

http://www.rodeoplasticbag.com/html/construction_film.html

http://www.poly-america.com/Products/Sheeting.html

http://www.polar-plastics.com/PolySheeting.htm

Did you know ?

The wonderful folks at the Ethyl Corporation who brought you leaded gasoline have never been sued for contaminating the ground with lead 

To create large pond liners, you have to splice big sheets of Visqueen film together.  In the olden days, they used to roll up dynamite fuses in the film and light it to make a seal.


The largest blown film line in North America is located at Poly America in Grand Prairie, TX.  Although Poly America's roots are in C & A film, their mainstay is private label trash bags.

Read More

Topics: poly film, visqueen, construction film

Plastics in-depth and insights

 

Plastic Blogs

Subscribe by Email

Most Popular Posts

Browse by Tag