Understanding Glass and Plastic Packaging Materials
Advantages:
- Lightweight
- Good oxidation and sulfidation resistance
- Sensory stability of the product
- Recyclable
Disadvantages:
- Low resistance to acidic foods
- Requires varnishing
- Sterilization containers controlled
- Difficulty with side seam welding (two pieces preferred over three)
Applications:
- Beer
- Carbonated beverages
- Easy open lids
- Fish
- Marine delicacies
Glass Containers: Glass is a supercooled liquid, non-crystalline, with a variable chemical composition and very high viscosity, resulting from the merger of organic oxides. It is a very complex silicate.
General Characteristics:
- Hard substance
- Brittle
- Twinkling appearance
- Insoluble
- Melts at approximately 1500 °C
- Poor thermal conductivity
Chemical Composition:
- Silicon Oxide (SiO2) silica or quartz: approximately 80%
- Sodium Oxide (Na2O): approximately 15%
- Calcium Oxide (CaO): approximately 15-20%
Desirable Physical Characteristics:
- Reasonable fusibility at elevated temperatures
- Adequate viscosity at that temperature
- Resistance to devitrification
- Maximum resistance to thermal-mechanical packaging
Features of Glass Containers:
- Mechanical protection for contents
- Physical and chemical inertness (does not deteriorate)
- Suitable for packaging food and beverages
- Transparent
- Washable and easy to clean
- Weatherproof against gases, moisture, and microorganisms (except UV light, which requires filters)
- High weight and fragility
- Poor thermal conductivity (30 times smaller than tin)
Fracture of Glass Containers:
- Impact Fracture: Caused by active impact or a series of small impacts.
- Factors: Damage to the inner or outer surface due to manufacturing defects, such as poor tempering or thickness.
- Stress Fracture: Internal faults located in the middle of the pack, often due to scratches or scrapes.
- Factors: Manufacturing defects (poor tempering, etc.), weight, pressure supported, size, and greater resistance.
- Thermal Shock Fracture: Occurs when one part of the glass is at a different temperature than another, causing mechanical stress fractures.
- Factors: Manufacturing defects (poor tempering, uniformity of thickness), thickness, effort, and breaking potential.
Lubricants or Glass Surface Treatments to Improve Resistance to Shock:
- Surface Lubrication: The packaging is annealed in atmospheres of SO2, with independent spraying of stearate, silicone, polyethylene dispersion, and metal oxides of titanium and black plate.
Vacuum Closures for Glass Containers:
- White Cap Closures:
- Pry-off: A steam jet creates a vacuum through condensation.
- Twist-off: A vacuum and lightweight twisted closure keeps the lid in place.
- Press-on Turn-off: A mixed system with screw vacuum.
Plastic: Derived from petrochemicals, gases are subjected to high temperatures and pressures, forming solid polymers of high molecular weight: resin pellets (granules) and powder.
Family of Plastics for Food Packaging:
- Polyolefins: PE (polyethylene), PP (polypropylene), PS (polystyrene), PVC (polyvinyl chloride), PVDC (polyvinylidene chloride, Saran).
- Polyester: PEN (polyethylene naphthenate), PET (polyethylene terephthalate).
- Polyamides: PA (nylon 6), PA (nylon 11), PA (nylon 12).
- Others: EVOH (ethylene vinyl alcohol), ABS (acrylonitrile butadiene styrene).
Plastic Barriers to High Temperatures:
- HDPE: Packaging for boil-in-bag (herbs in the bag).
- PP: High temperature resistant, suitable for microwave packaging and retort pouches.
- PVDC: Plates ready for use.
- PET: Used for retort pouch laminating.
Types of Plastic Materials for Food Packaging:
- Leaves (Film) and Simple Strips: Calendered, extruded.
- Film and Sheet Complex: Laminates, co-extruded.
- Retort Flexible Packaging (Plastics):
- Retort Pouch: Recommended for cooking, pasteurization, or sterile vacuum. Replaces canned food and allows for long-term food preservation (approximately 18 months).