Microbial Entry and Gas Permeability Quiz

Introduction

• Food packaging materials traditionally rely on non-renewable resources.
• There's a growing focus on sustainable, renewable packaging such as plant-based products and fermentation by-products.

Edible Films and Coatings

• These are used to extend the shelf life of food items and protect them from environmental factors.
• Benefits include consumption with the product, reduced residual packaging, enhancement of food's organoleptic properties, nutritional value enhancement, individual food portion packaging, application in heterogeneous foods, functioning as carriers for antimicrobial and antioxidant agents, microencapsulation of flavoring and leavening agents, and use in multilayer packaging materials with nonedible films.
• Advantages over traditional synthetic materials are prominently highlighted.

Polysaccharide-Based Coatings

• Polysaccharides and their derivatives (alginate, pectin, carrageenan, starch, etc.) are used as edible films or coatings.
• These polymers have limited moisture-barrier properties due to their hydrophilic nature.

Lipid-Based Coatings

• Derived from lipids (fats), used as protective barriers in food packaging.
• Effective in preventing water movement.
• However, they aren't ideal for strong structural support.

Protein-Based Coatings

• Made from animal and plant proteins (collagen, gelatin, milk proteins, cereal proteins).
• Good barrier properties against oxygen and moisture.
• Susceptible to proteolytic enzymes, especially in high humidity conditions.

Multicomponent Films

• Combination of different materials for structural strength and protective properties.
• Typically composed of a lipid layer for moisture resistance and a polysaccharide or protein layer for structural integrity and functionality.
• Often compared to synthetic films (LDPE) but with varying water and oxygen barrier properties.
• Combining edible waxes or fatty acids significantly improves their water vapor and oxygen barrier traits.

Biobased Packaging Materials

• First-generation materials: synthetic polymers (LDPE) with 5 to 20% starch fillers
• Second-generation materials: synthetic polymers (40 to 75% gelatinized starch) and addition of hydrophilic copolymers (partially biodegradable).
• Third-generation materials: fully biobased and biodegradable materials (PHAs).

First, Second, and Third Generation Biobased Polymers

• First generation polymers: 5% to 20% starch with LDPE and additives. Biofragmentation, not biodegradation.
• Second generation polymers: 40% to 75% gelatinized starch with LDPE and copolymers. 40-day starch degradation, 5-year total degradation.
• Third generation polymers: entirely biobased, broken down into three categories from extracted biomass or produced from biomass monomers.

Food Packaging Applications of Biobased Polymers

• Limited use in general, despite significant research and various studies.
• PLA (polylactic acid) most viable commercial polymer, suitable for food wrapping, thermoformed goods for bakery, and biodegradable food service containers.
• Offers key benefits in reducing reliance on fossil fuels and CO2 emissions compared to petrochemical alternatives.
• Fully compostable.

Properties of Biobased Packaging Materials

• Poor barrier properties under high humidity.
• Starch-based films have WVTRs (water vapor transmission rates) that are 4-6 times higher than conventional films.
• Polyhydroxyalkanoates (PHA) have WVTRs similar to Low-Density Polyethylene (LDPE).

Food Packaging Applications of PLA

• Beverage cups (used in major Olympic Games)
• Niche market for PLA trays and films (especially for vegetables and fruits).
• Potential use for short-life food packaging items (such as salads, eggs).
• Products that are minimally processed and fruits/vegetables.

Environmental Aspects of Biobased Packagings

• Biobased materials have lower environmental impacts than their petrochemical counterparts.
• Energy needed for PHA production is high (2.39 pounds of fossil resources vs. 2.26 pounds).

Permeability of Thermoplastic Polymers

• Packages are permeable to small molecules (gases, water vapor, organic vapors).
• Two mechanisms for permeation: pore effect (gaps and holes) and solubility-diffusion effect (dissolution and diffusion).
• Factors influencing permeability: pressure, temperature, and sorption (absorption).

Migration

• Release of initial compounds from packaging.

Measurement of Permeability

• Several methods for measuring gas permeability.
• Pressure and volume increase methods.
• Concentration increase method.
• Detector film methods.

Factors Affecting Diffusion & Solubility Coefficients

• Pressure increase with permeated gas.
• Temperature has a significant effect on solubility coefficients.
• Sorption is a process used in combination of both adsorption and absorption.

Processing and Converting of Thermoplastics

• Extrusion: primary method for producing sheets and films.
  • Monolayer extrusion: single polymer type.
  • Coextrusion: multiple polymers for layered films.
• Calendering: processes plastic between rollers for thin uniform sheets or films.
• Coating: applying liquid/melted substances to a substrate (surface treatment)
• Laminating: bonding multiple layers (e.g., plastic to paperboard).
• Metallization: adding a metal layer (e.g., aluminum) to a substrate.
• Orientation: aligns polymer chains for enhanced strength and properties.

Shrink Films

• Made of polyolefins, PVC, or PVdC.
• Shrinking requires heat.

Stretch Films

• Introduced in the 1970s, for wrapping large items.
• Common materials include LDPE, LLDPE, PVC, EVA copolymer, and PP.

Cross-Linking

• Chemical bonding to improve strength, heat resistance, and durability.

Microperforation

• Creates breathable films (especially for products with high respiration rates).

Injection Molding

• Process for shaping thermoplastics into products (e.g., containers, caps, preforms).
• Three main steps: feeding, melting, and injecting.

Blow Molding

• Creates hollow objects (e.g., bottles).
• Molten plastic (parison) expands inside a mold.

Stretch Blow Molding

• Biaxial orientation to produce high strength bottles (e.g., for carbonated beverages).

Foamed Cellular Plastics

• Plastics with reduced density due to numerous cells.
• Common materials include polystyrene.

Heat Sealing

• Process to bond materials using heat and pressure.
• Different sealing methods include conductance, impulse, induction, and ultrasonic.

Dielectric Sealing

• Using high-frequency current for bonding.

Hot-Wire Sealing

• Uses a heated wire for sealing (especially polyethylene bags).

Testing of Heat Seals

• Methods to evaluate the strength of heat seals. (Dynamic and static load tests).

Glass

• Amorphous (non-crystalline) structure that exhibits varying properties.
• Types: soda-lime, borosilicate.
• Applications: food, lab, and other products based on its special properties.
• Impact resistance and thermal shock resistance are crucial for glass containers.

Paper and Paperboard

• Raw material: pulp (fibrous).
• Types: Kraft, bleached.
• Processes: pulping, forming, pressing, drying, calendering, coating.
• Applications: folding cartons and boxes.

Molding Pulp Containers

• Made from aqueous slurry of cellulose fibers to create various containers (especially for foods).

Important Points in Printing Processes

• Relief (letterpress and flexography).
• Gravure (rotogravure).
• Lithography (offset litho and letterset).
• Screen printing
• Digital (Ink-jet and electrophotography (EP)).

Inks

• Different types of inks for various processes.
• Paste based: better for offset lithography and letterpress.
• Liquid based: faster drying, suitable for most processes

Adhesives

• Water-based, hot melt, solvent-based.
• Important materials in packaging, bonding parts together, and ensuring structural integrity.

Test your knowledge on the factors influencing microbial entry in packages and the properties of gases permeating through polymers. This quiz covers concepts such as permeability coefficients, selectivity ratios, and the extrusion process used in film production. Dive into the intricate details of polymer science and gas behavior!