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Plastic as a Packaging Material
Dr. Anil Pethe
What are plastics?Plastics may be defined as any group of substance, of natural or
synthetic origins, consisting chiefly of polymers of high molecular weight, that can be moulded into a shape or form by heat & pressure.
They usually consist of large molecules of organic materials which are based on certain building block molecules, undergo a process known as polymerization, a plastic or long chain polymer is produced.
Other material such as accelerators, initiators, solvents & catalyst can be added during polymerization to improve the characteristics.
AdvantagesLight weightReduced volume (warehousing & distribution cost reduction)No corrosion problemsGood resistance to mould & bacteria.Generally inert chemically, but be wary of “solvents”Usually have good impact strength; difficult to break, if breakage
occurs fragments tend to be less hazardous than glass.Wide design & decorative possibilities.
DisadvantagesNo plastic is totally impermeable to moisture, gases etc.Most plastics permit some passage of light. Even highly pigmented plastics & those with UV absorber are likely to let certain wavelengths through. Many are difficult to clean or are liable to attract dust & dirt under unfavorable conditions.May be permeable to, or subject to attack by, organic substances, particularly solvents.Subject to adsorption or absorption according to formulation ingredient.Light weight & thin wall section may require specific production line handling.Fully effective closing systems are sometimes difficult to achieve.Certain designs may show panelling or cavitation
Types of Plastics
1) Thermoplastic Polymers- These are heat softening materials which can be repeatedly heated, made mobile & then reset to a solid state by cooling.- Under conditions of fabrication they can be moulded by
temperature & pressure.- Eg. Polyethylene, PVC, polystyrene, polypropylene, nylon, polyester2) Thermosetting Polymer- These are polymers produced by a polymerization process involving
a curing or vulanisation stage during which the material becomes ‘set’ to a permanent state by heat & pressure.- Further heating leads to decomposition of the plastic.- Eg. Phenolics, melamine, urea, alkyds, epoxides, certain polyesters &
polyurathanes, cross linked polymers.
Plastics Used For Packaging1. High Density Polyethylene (HDPE)
Characteristics: Low – cost Moderately flexible Stiffer and has better barrier properties Chemical resistant Poor clarity Translucent in natural state and can be tinted with any opaque color. Odorless and tasteless
Advantages Low-cost Good moisture barrier Not attack by most solvent
Disadvantages Poor barrier for oxygen & other gases Odors and flavors are sometimes lost Perfume or flavoring oil can transpire rapidly Stress-crack in the presence of some product
Applications For thin-wall blow- moulded containers Injection moulding of closures Rotational moulding for large containers such as
carboys Industrial and consumer bags and thermoformed
2. Low Density Polyethylene (LDPE)
Odorless and tasteless Easily blended with such copolymers Highly resistant to most solvent Poor barrier for gases Softening temperature is around 210ºF Easily pigmented Good transparency Translucent and waxy in thick-walled container
AdvantagesFlexibleMoisture barrierToughChemical resistantLight weightLow costHeat sealable
DisadvantagesNot practical for rigid container and flexible packages
Problem in flavors and odorsStress crackingNot recommended for oily products
Applications: Use in squeezable tubes and bottles
Wrappers and bags for different products
Thermoformed into trays, frozen food containers
Coating material for bottle cartons, bacon wrappers and paperboard milk containers
3. Linear Low Density Polyethylene (LLDPE)Characteristics:Low-cost Light weight Superior toughness Rigid Flexible Moisture barrier Chemical and stress-crack resistant
Advantages:- Good tensile strength- Puncture resistance- Good impact and tear properties- Stress cracking and warding resistance
Application:- For large-sized bagging and wrappingoperations
4. Polypropylene (PP)
Characteristics: Heat and chemical resistance Tough & rigid Resist oil and greases Stress-crack resistance Fairly good barrier to moisture and gases High melting point
AdvantagesLight weightLow-costLess shrinkage
DisadvantagesLow impact strengthSharp melting point
Applications:Widely used in closures of all kindsSuitable for some boil-in-bag packages and containers
Standard plastic in moulded container
5. Polyvinyl chloride (PVC)
Characteristics:Crystal clear Low in impact strength Tough and has good puncture resistance
Good barrier properties (moisture and gases)
Retains odors and flavors
AdvantagesRelatively inexpensiveTough clear
Disadvantages • Corrosive when overheated• Yellows when exposed to heat or UV light• Scratches easily seen
Applications:• Blister packaging for pharmaceutical and capsules
• Garment, box and pallet load wrapping applications
Characteristics:• Structurally strong• Relatively low moisture absorption• Good dimensional stability• Heat sealability
Advantages• Clear• Good barrier properties to gases• Excellent stability at both high and low temp.
Disadvantages• Can be oxidized causing nylon to lose strength
Applications: • Co-extruded with poly-olefins to enhance packaging properties
• Coating on paperboards, papers and foils• Extrusion-blow-molded containers for hard to-hold chemicals
7. Polyester (Polyethylene Tetraphthalate)
Characteristics:• Excels in strength, toughness and clarity
• Resistant to weak acids, bases and most solvents
• Not good barrier for gases
Advatages• Fairly stiff material• Excellent transparency• Excellent heat, low• temperature and water resistance• Excellent oil, chemical and solvent resistance• Excellent barrier to aroma and Flavor
Disadvatages• Poor seal property• High cost
8. Polystyrene (PS)
Characteristics:• Crystal clear and very hard, brittle and rigid• Low melting point (190ºF)• Poor impact strength• Not good barrier for moisture or gases• Odorless and tasteless
Advantages• Clear and light weight• Low in cost• Easily molded, thermoformed and extruded into film
• Accept printing, metallizing and hot-stamping
Disadvantages• Slight tendency to shrink• Discolor in strong sunlight• Can craze and become cloudy• Builds up static changes Easily
• Applications: • Bottles for pharmaceutical tablets and capsules
• In molded forms for close containment of fragile products
Characteristics:• Good clarity, impact strength, ductility and
low controllable mold shrinkage• Sterilizable and tolerates gamma radiation
• High-priced material
Advantages• Great clarity, toughness and high softening temp.
• Dimensionally stable and processable
• Odorless and non-staining
Disadvantages• High- cost• High permeation of moisture and gases
• Sensitive to oxygen and carbon dioxide
Plastic Processing :1. Injection Molding- Grains of polymer are mixed and heated by a screw in a molding machine and injected under a high pressure into a cool mold.
2. Compression Molding- powdered resin is put into a heated mold- mold closes under high pressure- Plastic cures in a minute, then molds open.
3. Rotational Molding- also called rotomolding or rotational casting- Produces seamless, hollow parts of uniform thickness and without the internal stresses that can be created during conventional molding or thermo forming
Rotational Moulding Process
4. Blow Molding- similar to glass making and used either a single or two stage process for producing bottlesa. Extrusion Blow Molding- continuously extrudedtube of softened polymertrapped between two halvesof mold and inflated bycompressed air to the shapeof the mold.
b. Stretch Blow Molding- a preform is injection or extrusion- reheated to produce biaxial orientaton of the molecules and finally stretch blownc. Injection Blow Molding- polymer is injection molded around a blowing stick , then transferred to blowing mold.- compressed air is used to form final shape of container
5.Thermoforming - film is softened over a mould, and a vacuum and/ or pressure is applied
Typical Technologies of Converting To give new processing to yield new value on the rolls that are wound thin substrates which are plastics film sheet, paper, foil and cloth.1. Coating- Thin membrane that is coated liquid on the film sheet- Process of applying one or more layers of polymer latices or polymer melt to the surface of a substrate2. Laminating - made multiple layers by adhesives and extrusion molten resin
3. Printing- to express conveyance of eye information and ornament
4. Metallizing- metals are vaporized and adhere to substrate
5. Embossing- of set of concave-convex design to substrate by embossing roll- to make soft-feeling and mat surface6. Slitting- film sheet is continuously slit constant position width of the product for secondary processing7. Winding- is of set purpose to adjust edge of roll product and get rid rejective part.
Constituents in Plastic• Plasticizers• Fillers, Extenders, Lubricants• Stabilizers• UV absorber• Slip additives/ anti-slip additives• Anti-blocking agents• Colourants-pigments & dyes• Antioxidants• Internal release agent• Inhibitors (mould or bacteria inhibitor)• Toughening agents- impact modifiers• Flame-retarding agent eg- opacifiers, whitening agnet
Plasticizers• Plasticizers improve the flow properties of material, increases softness & flexibility, & are found mainly in polyvinyl chloride (plasticised PVC) and the cellulosics.
• The most common PVC plasticizers are phthalate esteres, phosphate esters, sebacate & adipate esters, polymeric plasticizers.
Fillers• Filler is an inert solid substance • Eg- carbon black, chalk or calcium carbonate, china clay, silica & magnesium carbonate
• The maximum limit of filler is upto 1:1 ratio , after which the binding power with the plastic is lost.
Toughening agent/ impact modifiers
• A few plastics which tend to be naturally brittle require an improvement in both Their drop (impact) strength & their top loading (compression) strength.
• In the case of polystyrene ,rubber is widely used as an impact modifier.
• Rigid PVC, when used as container may suffer weakness when subjected to 3-4 feet drop test & hence 15% of methyl methacrylate butadiene styrene (MBS) copolymer is added to improve impact strength.
Lubricants• lubricants may be added either as an additive or at the fabrication stage as a processing aid.
• In general lubricants prevent adhesion with metal part.
• Lubricants may also improve the flow & thereby lower the temperature of the moulding operation.
• Eg in silicone polydimethyl siloxane may be used in LDPE & HDPE films to improve flow.
• Lubricants may be solid, such as waxes, stearates or liquid such as liquid paraffin.
Stabilizers• Stabilizers increase the stability of plastic
either during processing or during the moulded life of the material
• Stabilizers are frequently used to combat the combined effects of heat & light.
UV Absorber• UV absorber may be used for two reason:1.To protect the plastic from UV degradation2.To prevent the product degradation due to UV
rays passing through the plastic.• Chemically UV absorber may be based on
substituted phenols or bezophenones.• Eg- 2-hydroxy-4-n-octoxybenzophenone, &
other benzophenones .• Iron oxide & carbon are also used.
Slip additives• Slip additives are widely used for films either made or used on relatively High speed equipment where any non-slip or drag properties might be detrimental to out put.
• The most used slip additives are oleamide & stearamide, since they operate at the film surface they can be physically removed by abrassion.
Anti-slip additives• These were primarily developed to provide good bonding for palletsied loads of plastic sacks & bag
• Without the additives plastic sacks would tend to destack & slide off when the pallet is moved or jerked.
Anti-blocking agent• Both reel wound & sheet stacked materials may be difficult to separate due to blocking
• This may be caused by the smoothness of two surfaces giving rise to surface adhesion.
• It can be prevented by incorporation of finely divided silica or diatomacous earths eg. Mica
Antioxidants• Used to prevent oxidative degradation of certain plastics
• Polymers may be subject to various forms of oxidative attack during all stages of their life cycle.
• Eg. BHT,BHAColourants
Dyes & pigments are used
Extenders• These are somewhat similar to fillers• They are used as lower cost substitute for plastic
Internal release agent• These agents are somewhat similar to lubricants in that they provide release, particularly from metals eg mould
• zinc , calcium & magnesium stearate.
Inhibitors• Used to prevent microbial growth
Plastics used for pharma packaging• Plastic Containers• Plastic Collapsible Tubes• Plastic Closures• Blister Material• Plastic Pouch
Plastic ContainersAdvantages• Easily Formed• Freedom Of Design• Extreme Resistant To Breakage
• Light Weight
Plastic Collapsible TubesAdvantages:• Low In Cost,• Light In Weight,• Durable, Flexible• Pleasant To Touch,• Unbreakable, Leak Proof,• Odorless & Inert To Most Chemicals• Able To Retain Their Shape Throughout Their Use
• Unique Suck Back Feature
Disadvantages• Permeation Of Gases
Plastic Closures• The closure is an integral part of the pack, hence the word ‘pack’ covers the both the container & the closure system.
• The pack is only as effective as the closure employed, a successful marriage between container & closure is essential to the product shelf life & its acceptance during use.
• These are plastic devices which are used to prevent the contents from escaping and allow no substance to enter the container.
Types of closures 1.Screw-on closures
5.Press on closures
Blister PackAdvantages• Excellent environmental protection
• Pleasing & efficacious appearance
• User convenience• Child resistance• Tamper resistanceBlister Material
• Polyethylene• Polystyrene / Polypropylene
• PVC• Polyvinylidene Chloride• Polychlorotrifluoroethylene
Plastic PouchAdvantages• Ease of handling• Used for unit dosage
Materials used:• Polyethylene• Ethylene Vinyl Acetate
Plastic DefectsClass-A defects
• Cracks and breaks anywhere in the container• Any spot at heel or shoulder• Rough cut off at finish, leading to leaky closure• Weld lines that permit stress cracking in contact with product.
Class-B• Below minimum weight• Any dimension outside of limit• Uneven colour• Rough or orange peel surface
Class-C• Blotchy or incomplete printing• Streaky pigmentation• Plastic trim in boxes delivered with closures• Improper identification of cases.
Evaluation of Plastic
• Physical • Chemical• Biological