Biodegradable Films for Brighter Future

 By: Matthew Tabassi

Biodegradable Films

Biodegradable film technologies have enjoyed a tremendous increase in demand from the marketplace. This is largely due to an increased awareness of the environmental and performance attributes and benefits that these technologies bring to their users. Recent developments in polymer technology, manufacturing processes and complementary chemistries have provided possibility of the future generation of Biodegradable products to enter the marketplace. These products Include agriculture films, anti-static films, stretch films, masking films and films for other high technology applications. As these products become available globally, a much larger range of industries can effectively realize the environmental, economic and performance benefits of biodegradable technologies.

What is Biodegradable?

According to the FTC’s Green Guides, a product is biodegradable as long as it “will completely break down and return to nature (i.e., decompose into elements found in nature) within a reasonably short period of time after customary disposal.” In other words, the item will continue to disintegrate into small pieces until micro-organisms consume it.

The U.S. Federal Trade Commission (FTC)

Biodegradable polymers

• Process by which organic substances are broken down by the environmental effects and by the living organisms.

• Organic material can be degraded aerobically or anaerobically .

• Biodegradable matter is generally organic material such as plant and animal matter and other substances originating from living organisms, or artificial materials that are similar enough to plant and animal matter to be put to use by microorganisms.

• Biodegradable polymers are a kind of materials which degrades biologically.

• The biodegradability of plastics is dependent on the chemical structure of the material and on the constituent of the final product, not just on the basic materials used in the production.

Biodegradable Range

• Starch based products including thermoplastic starch, starch and synthetic aliphatic polyester blend, and starch and PVOH (polyvinyl alcohol) blends.

• Naturally produced polyester including PVB (polyvinyl butadiene).

• Renewable resource polyesters such as PLA (poly lactic acid).

• Synthetic aliphatic polyesters including PCL (poly caprolactone).

• Aliphatic-aromatic (AAC) co polyester.

• Hydro-biodegradable polyester such as modified PET.

• Water-soluble polymers such as polyvinyl alcohol and ethylene vinyl alcohol.

• Photo-biodegradable plastics.

• Controlled degradation additive master batches.

Classes of Biodegradable

• Compostable

• Hydro-biodegradable

• Photo-biodegradable

• Bioerodable

• Biodegradable

Starch-Based Polymers

• Our work relates to a biodegradable film prepared by chemical bonding of starch and polyethylene.

• Polyethylene is polyolefin having the most widest general application, coupling agent such as maleic anhydride, methacrylic anhydride or maleimide which bonds with starch and polyethylene, and Lewis acid catalyst and to a process for preparing thereof.

Cornstarch

Common cornstarch has 25% amylose. The two remaining corn starches are high-amylose corn starches; one has 50% to 55% amylose, while the second has 70% to 75%.

Their size ranges between 5 microns and 20 microns

Mazie Starch

Maize starch has irregularly shaped granules. High-amylose starches also have an irregular shape, but tend to be smooth. Some of these are even rod-shaped. High-amylose starches have a narrower size range: 5 to 15 microns, or even 10 to 15 microns, depending on the variety.

Potato Starch

Potato starch has about 20% amylose. Potato starch granules are large with a smooth round oval shape. Of the starches commonly used for food, potato starch is the largest; its granules range in size from 15 to 75 microns.

Rice Starch

Common rice starch has an amylose: amylopectin ratio of about 20:80, while waxy rice starch has only about 2% amylose. Both varieties have small granule sizes ranging from 3 to 8 microns.

Tapioca Starch

Tapioca starch has 15% to 18% amylose. Tapioca granules are smooth, irregular spheres with sizes ranging from 5 to 25 microns.

Wheat starch

Wheat starch has an amylose content of around 25%. Its granules are relatively thick at 5 to 15 microns with a smooth, round shape ranging from 22 to 36 microns in diameter.

Soya Bean Starch

Soya bean starch has irregular shaped granules. Common Soya bean starch has 7% amylose. Its granules range in size from 10 to 90 microns.

Variety of Starch by Percentage

CATEGORIES OF STARCH BASED POLYMERS

• Thermoplastic starch products.

• Starch synthetic aliphatic polyester blend

• Starch PBS/PBSA polyester blends

• Starch PVOH blends.

Thermoplastic Starch Products

• Thermoplastic starch biodegradable plastics (TPS) have a starch (amylose) content greater than 70%.

• It is based on vegetable starch, and with the use of specific plasticizing solvents, can produce thermoplastic materials with good performance properties and inherent biodegradability.

• This can be overcome through blending, as the starch has free hydroxyl groups, which readily undergo a number of reactions such as acetylation, esterification and etherification.

Starch Synthetic Aliphatic Polyester Blends

• Blends of biodegradable synthetic aliphatic polyesters and starch are often used to produce high quality sheets and films for packaging by flat-film extrusion using chill-roll casting or by blown film methods

• Approximately 50% of the synthetic polyester (at approximately $4.00/kg) can be replaced with natural polymers such as starch (at approximately $1.50/kg), leading to a significant reduction in cost.

• Furthermore, the polyesters can be modified by incorporating a functional group capable of reacting with natural starch polymers.

Starch and PBS/PBSA Polyester Blends

• Polyesters that are blended with starch to improve material mechanical properties are Polybutylene succinate (PBS) or polybutylene succinate adipate (PBSA).

• At higher starch content (>60%), such sheets can become brittle.

• Plasticizers are often added to reduce the brittleness and improve flexibility.

• Starch and PBS or PBSA blends are used to produce biodegradable plastic sheet, which can be thermoformed into products such as biscuit trays or film products.

PVOH (PVA)

Starch-PVOH Blends

• Polyvinyl alcohol (PVOH) is blended with starch to produce readily biodegradable plastics.

MAJOR DISPOSAL ENVIRONMENTS FOR BIODEGRADABLE PLASTICS

• Composting facilities or soil burial

• Anaerobic digestion

• Wastewater treatment facilities

• Plastics reprocessing facilities

• Landfill

• Marine and freshwater environments

• General open environment as litter.

WASTE WATER TREATMENT PLANTS

• Activated sewage sludge will convert approximately 60% of a biodegradable polymer to carbon dioxide.

• The remaining 40% will enter the sludge stream where, under anaerobic digestion, it will be converted to methane.

• Any biodegradable polymer that meets the composability criteria will degrade even faster in a sewage environment.

MARINE AND FRESHWATER ENVIRONMENTS

• The rate of biodegradation in marine environments is affected by the water temperature.

• In cold waters, the plastic material may still be in a form that could endanger marine life for an extended period of time. It is found that plastic is fully degraded in 20-30 days in a compost environment .

• Thus seasonal and climatic effects on biodegradation rates need to be considered in relevant applications.

LITTER

• Plastic litter causes aesthetic problems as well as danger to wildlife resulting from entanglement and ingestion of plastic packaging materials and lightweight bags. Wildlife losses are an issue for the conservation of biodiversity, and losses due to litter have caused public concern.

Future of Biodegradable plastics

• It is estimated that plastic waste generation will grow by 15% per year for the next decade.

• There is room for growth and expansion in many areas of the biodegradable plastic industry.

• Researchers worldwide are interested in the area of biopolymer development.

• Organic recovery (composting spent materials) is the most commonly applied waste reduction method.

• The nature of natural materials requires different considerations than those for synthetic materials.

• The biopolymer industry has a positive future, driven mainly by the environmental benefits of using renewable resource feedstock sources.

• The ultimate goal for those working in development is to find a material with optimum technical performance, and full biodegradability.

TEST FORMULATION

Material                                         PHR

• LDPE                                         100

• Maize Starch                             5-400

• Maleic Anhydride                     0.01-10

• Stearic Acid                              0.01-6

• Di-Cumyl Per Oxide                 0.01-1.0

• Manganese Stearate                  0.01-10

• Viton                                         0.01-10

Polymers Chemically Bonded by Starch

EMERGING APPLICATION AREAS

FOOD PACKAGING

Wide ranges of food packaging can use Biodegradable film. More and more companies are switching to biodegradable and compostable films to help facilitate their sustainability initiatives.

AGRICULTURE MULCH FILM

These low-density polyethylene mulch films help vegetable producers achieve early, more lucrative markets by enhancing soil warming and earliness of crops. Biodegradable mulches of interest are those made from plant starches (corn or wheat) and are completely biodegrade in the soil.

SHOPPING BAGS

Biodegradable shopping bags can be made "oxo-biodegradable" by being manufactured from a normal plastic polymer (i.e. polyethylene) or polypropylene incorporating an additive which causes degradation and then biodegradation of the polymer (polyethylene) due to oxidation.

Liquid Detergents

This application hinges on the principle of using biodegradable water soluble packaging to deliver unit dosage amounts of liquid detergent products. Active concentrate of liquid detergent ingredients is packaged in biodegradable water soluble films.

Toilet Blocks

The biodegradable water-soluble film can be used to pack all toilet blocks which helps in storing the toilet cleaning detergents safely in hospitals, hotels and in individual homes thereby ensuring that all toilets remain germ-free and smell clean.

Powdered Detergents

Biodegradable water-soluble film for powdered detergent pouches usually contains powdered ingredients that effectively dissolve in water.

Conclusion

• The nature of natural materials requires different considerations than those for synthetic materials.

• The biopolymer industry has a positive future, driven mainly by the environmental benefits of using renewable resource feedstock sources.

• The ultimate goal for those working in development is to find a material with optimum technical performance, and full biodegradability.

PVC cling films processing

 

By: Matthew Tabassi

Intro

The use of PVC in the global markets continues to grow. In 2012, total 37.4 million tons of PVC worldwide was consumed (source:HIS/Vinnolit), although PVC has special significance for tube, profile and sheet production, it is also widely used in film manufacturing.

Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in construction because it is cheap, durable, and easy to assemble. PVC production is expected to exceed 56 million tons by 2017.

Global Polymer Market (208MMT)

PVC can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates. In this form, it is used in clothing and upholstery, and to make flexible hoses and tubing, flooring, to roofing membranes, and electrical cable insulation. It is also commonly used in figurines and in inflatable products such as waterbeds, pool toys, and inflatable structures.

In recent years however, researchers have noted health risks such as reproductive abnormalities and developmental effects in human. A number of substances have been identified as alternative plasticizers. These alternatives include citrates, sebacates, adipates, and phosphates.

They are being substituted in products that traditionally use phthalates, such as toys, childcare articles and medical devices.

Plastic food packaging film, popularly known as cling film, has literally revolutionized the food industry. It has become a major contributor to food safety, both protecting and preserving it. At the same time it is now regarded as an essential and cost-effective tool for food presentation.

Plasticized PVC films preserve the freshness of meat as they have high oxygen and water vapor transmission.  They are cost effective since they run satisfactorily on high-speed packing machines and are effective for display as they have good clarity and are resistant to handling due to their good elastic recovery and puncture resistance.  They have excellent cling and are easily heat-sealed

For catering and household use, thinner films with less plasticizers are supplied.  The benefits are the same as with meat wrapping with cling, clarity and strength being especially important.  

Yet for all its versatility and obvious benefits, there has been media speculation about its safety.   Cling film has been used in the USA and Europe for decades and scientific research has repeatedly shown it is perfectly safe to use.

Whatever material is chosen for packaging food there is always some transfer from the constituents of the package to foodstuffs.  A considerable amount of experimental work has been carried out to determine the migration from plasticized PVC into food.   This migration is at levels which are considered totally safe by health authorities and which fall well within European Union regulations.

PVC

PVC is a thermoplastic made of 56.5% chlorine, basically derived from industrial grade salt and 43.5% carbon that derived predominantly from oil / gas via ethylene.  This chlorine gives PVC excellent fire resistance; when PVC is set on fire, the flames go out as the fire source is removed due to the material’s self-extinguishing properties making it number one choice for the cable industry.

PVC is regarded as perhaps the most versatile thermoplastic resin, due to its ability to accept an extremely wide variety of additives: plasticizers, stabilizers, fillers, process aids, impact modifiers, lubricants, foaming agents, biocides, pigments, reinforcements. Indeed, PVC by itself cannot be processed! It must have at least a stabilizer, a lubricant, and if flexible, a plasticizers present.

Plasticized PVC films preserve the freshness of meat as they have high oxygen and water vapor transmission. They are cost-effective, since they operate satisfactorily on high-speed packing machines, and are effective for display, because they have good clarity. Their good elastic recovery and puncture resistance make them suitable for handling; they have excellent cling properties and can be easily heat-sealed

Average degree of polymerization of PVC resin

A good range of polymerization for PVC is around 1000 to 1300, if `P < 1000, the film mechanical properties are not good enough.  If`P > 1500, the extrusion processiblity is inferior because the viscosity of melt is increased, it is easy for degradation by the heat which is generated during extrusion process. The difference of degree of polymerization preferably is less than ± 300. 

Plasticizer

In cling film usually manufacturers are using Dioctyl Adipate or DOA as plasticizers. DOA is an ester of  n-octanoland  Adipic acid. Its chemical formula is C22H42O4.

DOA features flexibility at low temperatures, good electrical properties, good resistance to weathering, and good stability to heat.

DOA is used to produce clear films for food packaging applications. In addition, it is compatible with nitrocellulose, ethyl cellulose, most synthetic rubbers, and high-butyryl cellulose acetate butyrates.

Short chain esters are used as high-boiling, biodegradable, low toxicity solvents and antiperspirants. Long chain esters of  Adipic acid are used as lubricants for the functions of stability, superior lubricity, corrosion protection, biodegradability, and excellent performance at both high and low temperatures.

Adipic acid esters (C5 - C10) are used as low-temperature-resistant and low viscosity plasticizers for polymers and cellulose esters.

If the plasticizers is less than 20 % by weight, the elongation of film, fluid ability, and heat stability for long run production will be affected defectively, if the plasticizers is more than 30%, there is weak film stiffness. 

Epoxidized Soybean oil

Epoxy resins are used as adhesives and structural materials. A polymer containing unreacted epoxide units is called a polyepoxide or an epoxy.

Polymerization of an epoxide gives a polyether, for example ethylene oxide polymerizes to give polyethylene glycol, also known as polyethylene oxide. It will improve heat stability during extrusion process.

If the epoxidized soybean oil is less than 10% by weight, the heat stability is not excellent during extrusion process. If the Epoxidized soybean oil is more than 20% by weight, it might affect the color of film.

Stabilizer

The job of the stabilizer is to delay heat degradation so that the compound can be formed into a product before it degrades.

Normally Ca- Zn type stabilizers are using for the food packaging grade PVC cling film. The performance of more recent developments in calcium/zinc stabilizers also makes them potential technical alternatives to most other stabilizing systems, including lead and barium/zinc.

It normally adds in less than 1% by weight, preferably 0.8 –1.5%. If the stabilizer is less than 0.5, it is not stable thermally during extrusion process. If the stabilizer is more than 1 %, it will be bleed out on the film surface by long-term storage. Also it will take more time to gel with PVC resin and is difficult to mix homogeneously the resins during extrusion because of the slip property of stabilizer.

Anti-fog agent

Anti-fog agents, also known as anti-fogging agents and treatments, prevent the condensation of water on a surface in the form of small droplets which resemble fog.

Anti-fog treatments are often used for transparent glass or plastic surfaces in optics, such as the lenses and mirrors found in glasses, goggles, camera objectives, and binoculars.

Anti-fog treatments work by minimizing surface tension, resulting in a non-scattering film of water instead of single droplets, an effect called surfactant film or by creating a hydrophilic surface.

Lubricant

Lubricants are divided into two areas, internal and external lubricants. The transition between external and internal lubricating effect is fluid, however, – internal lubricants often also have a certain external lubrication effect and vice versa. Lubricants having both effects are therefore called “combined lubricants”.

Internal lubricants reduce the frictional forces occurring between the PVC molecule chains, thus reducing melt viscosity. They are polar and thus are highly compatible with PVC. They help achieve excellent transparency even at high dosages and do not tend to exudates, which helps optimizing welding, gluing, and printing properties of the final product.

External lubricants reduce the adhesion between PVC and metal surfaces. They are mostly non-polar such as paraffin and polyethylene waxes. The external lubrication effect is largely determined by the length of the hydrocarbon chain, its branching and its functional group. At high dosages they can lead to cloudiness and exudation.

MIXING AND COOLING

The mixer and coolers are the heart of the compounding system. This includes the control panels for mixer/coolers, silos, and conveying systems. These are computer controlled in more modern systems. The following two types of mixers are used in flexible compounding.

1. Low Intensive Mixer (LIM)

LIMS are ribbon blender-type mixers that are jacketed for heating and cooling. They have closed barrels and spiral blades which normally run about 25 to 75 RPM. The blades are designed to move the material to the center of the barrel providing good mixing. The tip speed is normally about 6 meters per second.

Frictional heating is very minimum, so this causes large heat gradients within the ribbon blender.

Depending on the hardness of the flexible PVC compound being made, mixing times can be from one to six hours. Batch size may be up to 5000 pounds. Heating and cooling must be provided to this type of mixer.

2. High Intensive Mixer (HIM)

HIMs are like kitchen blenders with very high RPM's (500 to 1500). They achieve most of their heating from frictional heat. Depending on the manufacturer, one can have a variety of blades and blade designs. There are 2 to 4 blades in a normal mixer. Three blades are typical for flexible mixing and four blades for rigid mixing. The blades are designed to give homogenization to the resin and other ingredients. The tip speed is normally around 30-40 meters per second. Mixer size ranges from 10 to 1000 pounds. A typical cycle time will be from 4 to 10 batches per hour.

It is very important to have a good, deep vortex during most of the mixing cycle. The material must always be turning over and achieve a dry state before dropping to the cooler. If one looks down into the mixer, the material goes through several states. As resin is added, there is an uneven flow.

When adding the plasticizer, this state continues. Around 160°F, the resin starts to absorb the plasticizer and the vortex decreases. The material must continue to turn over to get a good mix. At powder peak, all plasticizer is absorbed and the flow in the mixer is nice and smooth. Mixer amperage should be observed and/or recorded. HIMs give the most uniform temperature for the entire batch while achieving uniform temperature the quickest.

After mixing is complete, the powder material must be cooled by dropping it into a cooler. Cooling is usually done in a low intensive mixer. Water is pumped through the water jacket to speed the cooling process. Coolers may be ribbon blenders, round-like pots, or barrel type, all of which are closed-type bowls. Some have blades or plows. The blades have an RPM of 50 to 100 with a tip speed of 6 meters per second. After cooling, the material should be screened for mixer build-up and foreign material. Screen size is normally from 10 to 30 mesh depending on the end product to be extruded. 

High Intensive mixer for PVC compounding

Courtesy of Dermak Makina

Extrusion

PVC is non-crystallizable polymer commercially even though there was reported 5-10% of crystal existed in certain process. The polymer is heated to a temperature at which it becomes a viscous liquid, and then it is cooled homogeneously to as near as the glass transition temperature, is practical for stretching. The material is stretched mono axially or biaxially either at a constant temperature or under a falling temperature gradient, and is subsequently quenched to below glass transition temperature.

Glass transition temperature of PVC will be vary by adding quantity of plasticizer. PVC glass transition temperature reported 105 °C without the plasticizer and 60 °C by adding 15% plasticizer. The glass transition temperature decrease in proportionally to the number of polymer molecule of plasticizer as additives. PVC processing temperature range is from 135ºC to 200ºC

PVC Cling film

                            Courtesy of Flextrusion Sdn. Bhd. 

The specific environment condition required for PVC cling film winding

 Extrusion environment required at absolute humidity 0.014 – 0.024 kg/m³ from die to film passing distance within 1m on the casting roll. If the absolute humidity is less than 0.014 kg/m³, the quantity of moisture on surface of film react with antifogging agent is not enough, unwinding distance of film will be less than 1000mm and slip property is not good enough for packaging process. If the absolute humidity is more than 0.024 kg/m³, the quantity of moisture on surface of film react with antifogging agent is excess and unwinding distance will be more than 1500mm and cling property will be decreased besides the slip property of film.

The film temperature before winding recommends 30ºC -35ºC for preventing entrapping air inside film roll. If film temperature is less than 30ºC, the film will harden and then the air will be entrapped inside of roll, unwinding distance will increase; cling force of film will decrease. If film temperature is more than 45 ºC, there is no film stiffness and then easy to block each film layer, unwinding distance will be decrease.

The film will shrink by the residual stress of winded film during packing process. In order to release the stress, generally film is heat up under tension or without tension during film casting process. But it is difficult to eliminate wrinkles of PVC stretch film.

To release winding stress on the film properties, carry out aging at least 24 hours to 72 hours at 35-50°C after winding.

Degradation

When PVC is processed at high temperatures, it is degraded by dehydrochl ordination, chain scission, and cross-linking of macromolecules.

Free hydrogen chloride (HCl) evolves and discoloration of the resin occurs along with important changes in physical and chemical properties.

The evolution of HCl takes place by elimination from the polymer backbone; discoloration results from the formation of conjugated polyene sequences of 5 to 30 double bonds (primary reactions). Subsequent reactions of highly reactive conjugated polyenes crosslink or cleave the polymer chain, and form benzene and condensed and/or alkylated benzenes in trace amounts depending on temperature and available oxygen (secondary reactions).

The features of PVC cling film for food packaging

•       Excellent Oxygen permeability

•       Selective gas permeability

•       Good anti-fogging effect

•       Optimal stretching property

•       Sufficient elastic property

•       Excellent cold temperature application

•       Excellent cling property

•       Safe products for food packaging (all components are for food grade)

•       Transparent (See-through effect)

•       Thin gauge

•       Optimal machine-ability for automatic packing.

Conclusion

PVC cling wrap, commonly called cling film, is thin flexible PVC film often 8-10 microns with tear resistant properties.

Uncovered foods are at the risk of contamination from microorganisms and PVC cling film is a major contributor to food safety during transportation, distribution and storage of food products. Despite its versatility and obvious advantages, there has been substantial speculation about the safety of cling film.

Likely the key message is that all plasticizers are not the same and regulations statues of various plasticizers vary considerably! PVC cling film which compounded with an Adipate plasticizer has been safely used in food packaging for decades.

Food Grade PVC Cling film

                                                                               

References

1.       Loftus, N.J. Laird, W.J.D., Steel, G.T., Wilks, M.F. and Woollen, B.H. (1994) Metabolism and pharmacokinetics of deuterium labelled di-2-(ethylhexyl) adipate (DEHA) in humans.  Fd Chem. Toxic., 31 (9), 609-614.

2.       Loftus, N.J., Woollen, B.H., Steel, G.T., Wilks, M.F. and Castle, L. (1994). An assessment of the dietary uptake of di-2-(ethylhexyl) adipate (DEHA) in a limited population study. Fd Chem Toxic., 32 (1),1-5.

3.       www.plastics.com/content/articles/5/1/PVC--Polyvinylchloride-What-is-PVC/Page1.html/print/5

4.       http://www.baerlocher.com/products/lubricants/

5.       Oxy Vinyls, LP, Mixing Flexible PVC Compound, Technical Report #52

6.       A. Baruya , D. L. Gerrard , W. F. Maddams Resonance Raman spectrum of degraded poly(vinyl chloride). 4. Determination of conjugated polyene sequence lengths

7.       Phthalates and their Alternatives: Health and Environmental Concerns, by The Lowell Center for Sustainable Production at the University of Massachusetts

8.       DEHA Fact Sheet DEHA Fact Sheet 2012, South African Vinyls Association.