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Questions and Answers
Glass, paper, metal, and plastics are the only materials currently used for food packaging.
Glass, paper, metal, and plastics are the only materials currently used for food packaging.
False
Polymers are organic compounds created through the molecular alteration of lower molecular weight molecules.
Polymers are organic compounds created through the molecular alteration of lower molecular weight molecules.
True
Biobased plastics are made exclusively from synthetic materials.
Biobased plastics are made exclusively from synthetic materials.
False
The molecular structure of polymers does not affect their physical properties.
The molecular structure of polymers does not affect their physical properties.
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Modified Atmosphere Packaging (MAP) is a technique used to extend the shelf life of foods.
Modified Atmosphere Packaging (MAP) is a technique used to extend the shelf life of foods.
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Aseptic packaging is primarily used for packaging solid food items.
Aseptic packaging is primarily used for packaging solid food items.
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Surfaces of edible packaging can be made from materials such as polylactic acid.
Surfaces of edible packaging can be made from materials such as polylactic acid.
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Active and intelligent packaging systems do not contribute to food safety and quality.
Active and intelligent packaging systems do not contribute to food safety and quality.
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Thermosetting polymers can be remolded and reshaped after manufacturing.
Thermosetting polymers can be remolded and reshaped after manufacturing.
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Thermoplastic elastomers are polymers that can stretch and then return to their original form.
Thermoplastic elastomers are polymers that can stretch and then return to their original form.
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Polyolefins are polymers made from olefin monomers.
Polyolefins are polymers made from olefin monomers.
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Linear polymers are classified as thermosetting polymers.
Linear polymers are classified as thermosetting polymers.
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Thermoplastic materials are the major packaging material used in the food industry.
Thermoplastic materials are the major packaging material used in the food industry.
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Cross-linked polymers can melt upon heating due to the presence of cross-links.
Cross-linked polymers can melt upon heating due to the presence of cross-links.
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Mechanical properties of thermoplastic polymers are temperature sensitive.
Mechanical properties of thermoplastic polymers are temperature sensitive.
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Additives in plastics typically include surface property modifiers and antiaging additives.
Additives in plastics typically include surface property modifiers and antiaging additives.
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Condensation polymerization involves two active sites joining together with no small molecules being ejected.
Condensation polymerization involves two active sites joining together with no small molecules being ejected.
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Thermoplastic polymers can only be formed by addition polymerization.
Thermoplastic polymers can only be formed by addition polymerization.
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The degree of polymerization (DP) can be as high as approximately 100,000.
The degree of polymerization (DP) can be as high as approximately 100,000.
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Weight average molecular weight (Mw) is always smaller than number average molecular weight (Mn).
Weight average molecular weight (Mw) is always smaller than number average molecular weight (Mn).
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The average molecular weight of polymers can be precisely defined.
The average molecular weight of polymers can be precisely defined.
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As the degree of polymerization increases, the substance transitions from light oil to solid.
As the degree of polymerization increases, the substance transitions from light oil to solid.
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Density of polymers is only influenced by the number of repeating units in a molecule.
Density of polymers is only influenced by the number of repeating units in a molecule.
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Hydrocarbon polymers tend to have a high mass per unit volume.
Hydrocarbon polymers tend to have a high mass per unit volume.
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Polymers containing chlorine can have densities significantly higher than those of amorphous hydrocarbon polymers.
Polymers containing chlorine can have densities significantly higher than those of amorphous hydrocarbon polymers.
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There is no relationship between crystallinity and the toughness of oriented films.
There is no relationship between crystallinity and the toughness of oriented films.
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Non-crystalline, amorphous polymers do not exhibit a defined melting point.
Non-crystalline, amorphous polymers do not exhibit a defined melting point.
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The crystallization rate is enhanced by the presence of impurities such as catalysts and fillers.
The crystallization rate is enhanced by the presence of impurities such as catalysts and fillers.
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High molecular weight and narrow molecular weight distribution contribute to low crystallinity in polymers.
High molecular weight and narrow molecular weight distribution contribute to low crystallinity in polymers.
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Cooling a molten crystallizable polymer does not lead to nucleation.
Cooling a molten crystallizable polymer does not lead to nucleation.
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Stretching a film can help to realign molecules and increase the total crystallinity of the film.
Stretching a film can help to realign molecules and increase the total crystallinity of the film.
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Crystallites in polymers are composed of whole molecules of uniform size.
Crystallites in polymers are composed of whole molecules of uniform size.
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Noncrystalline polymers undergo a melting transition at the glass transition temperature (Tg).
Noncrystalline polymers undergo a melting transition at the glass transition temperature (Tg).
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Chain ends and low-MW plasticizers increase the glass transition temperature (Tg) of a polymer.
Chain ends and low-MW plasticizers increase the glass transition temperature (Tg) of a polymer.
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For unsymmetrical chains, the approximate relationship is Tg ≈ Tm/2.
For unsymmetrical chains, the approximate relationship is Tg ≈ Tm/2.
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Above the glass transition temperature (Tg), carbon atoms in polymer chains can move with relative freedom.
Above the glass transition temperature (Tg), carbon atoms in polymer chains can move with relative freedom.
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Copolymers generally have a narrower temperature range for glass transition compared to homopolymers.
Copolymers generally have a narrower temperature range for glass transition compared to homopolymers.
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Crystalline copolymers have a higher melting temperature than their corresponding homopolymers.
Crystalline copolymers have a higher melting temperature than their corresponding homopolymers.
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Ordered copolymers exhibit different transition behavior from random copolymers.
Ordered copolymers exhibit different transition behavior from random copolymers.
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At sufficiently high temperatures, a thermoplastic polymer takes on a solid state.
At sufficiently high temperatures, a thermoplastic polymer takes on a solid state.
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If both Tm and Tg of a polymer are below room temperature, the polymer is a solid.
If both Tm and Tg of a polymer are below room temperature, the polymer is a solid.
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The glass transition temperature (Tg) of PVC is lower than that of PVdC.
The glass transition temperature (Tg) of PVC is lower than that of PVdC.
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The presence of bulky side groups in a polymer increases its glass transition temperature (Tg).
The presence of bulky side groups in a polymer increases its glass transition temperature (Tg).
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Polymers such as PET tend to have relatively low Tg values due to their stiff chain structure.
Polymers such as PET tend to have relatively low Tg values due to their stiff chain structure.
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The ASTM International Resin Identification Coding System was developed in 1988 and is intended to identify the plastic resin in products.
The ASTM International Resin Identification Coding System was developed in 1988 and is intended to identify the plastic resin in products.
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Increasing molecular symmetry in a polymer typically lowers its melting temperature (Tm).
Increasing molecular symmetry in a polymer typically lowers its melting temperature (Tm).
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Methyl groups on polypropylene (PP) raise its melting temperature (Tm) compared to low-density polyethylene (LDPE).
Methyl groups on polypropylene (PP) raise its melting temperature (Tm) compared to low-density polyethylene (LDPE).
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The values of Tm and Tg do not significantly affect the physical properties of thermoplastic polymers.
The values of Tm and Tg do not significantly affect the physical properties of thermoplastic polymers.
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Study Notes
Food Packaging
- Packaging materials used for food include plastic, glass, paper and metal.
- Different food categories have different packaging needs
- Modified Atmosphere Packaging (MAP) and Aseptic Packaging are examples of packaging techniques.
- Active and intelligent packaging are also important for food.
- Packaging design and material properties affect the shelf life and end use of packaged foods.
- Packaging must meet regulations from bodies such as the FDA and EU.
Packaging Materials
- Various materials are used for food packaging, accepted by regulatory bodies.
- Factors like design and material properties affect the package's end use and shelf life.
- Glass, paper, metal, and plastics are primary groups used.
Plastics
- Polyolefins, substituted olefins, copolymers of ethylene, polyesters, and polyamides are plastic types.
- Bioplastics include materials like starch, chitosan, polylactic acid, poly(hydroxyalkanoates), biopolyethylene, and regenerated cellulose film.
- Biopolyethylene terephthalate is also a type.
Classification of Polymers
- Thermoset: Permanent cross-linked, cannot be melted (e.g., tires, rubber bands).
- Thermoplastic: Meltable and moldable; these polymers return to their original form after stretching (e.g., soles of tennis shoes, many food packaging solutions).
- Elastomers: Polymers that stretch and return to their original form. Often thermoset.
- Polymer families: Polyolefins (from olefins), polyesters, amides, urethanes (using specific monomers, ester, amide, urethane bonds).
- Natural polymers: Polysaccharides, DNA, proteins.
Molecular Structure: Classification of Polymers
- The first group are linear polymers, which gradually soften and eventually melt with increasing temperature due to the independently moving polymer chains.
- The second group are cross-linked polymers, called thermosets, that become set into a network structure when manufactured. They retain this form and cannot be remolded.
- At high temperatures, irreversible chemical degradation may occur.
Polymerization Process
- Thermoplastics form by joining monomers.
- Under suitable conditions (temperature, pressure, catalyst), chains grow by adding monomers.
- Branching can occur but cross-links are typically absent.
- Addition polymerization joins monomers to create polymers with the same atoms in the repeating units.
- Some processes create orderly branches (isotactic), others are random (atactic).
Condensation Polymerization
- Starting monomers are not identical to the end polymers, and side groups are ejected during monomer addition.
- If sufficient side groups remain, rapid branching and highly cross-linked structures are formed.
Addition vs. Condensation Polymerization
- Addition polymerization involves unsaturated monomers and a rapid process to produce high molecular weight polymers.
- Condensation polymerization involves saturated monomers, a slow process, and lower molecular weight polymers.
Molecular Structure Summary
- Thermoplastic polymers can form via addition or condensation polymerization.
- Thermosetting polymers form only via condensation polymerization.
- The degree of cross-linking in a polymer varies widely.
Molecular Weight
- Degree of polymerization (DP): The average number of repeating units in a polymer molecule.
- Low DP values result in substances like light oils (e.g., paraffin from ethylene).
- Increasing DP leads to a transition through greasy, waxy, and then solid polymer states.
- DP can reach very high values.
Molecular Weight of Polymers
- Measuring molecular weight involves methods like size exclusion chromatography and viscosity measurements.
- Number average (Mn), weight average (Mw), and viscosity average (Mv) represent different ways to describe polymer molecular weight.
Density
- Density depends on chemical composition and how molecules pack together.
- Hydrocarbon polymers have lower densities.
- Materials containing oxygen, chlorine, fluorine, and bromine increase density.
Crystallinity
- Crystalline areas (crystallites) form when molten polymers cool, spreading out from nuclei.
- Length and entanglement of polymer chains disrupt complete crystallization, unlike low-molecular weight materials.
- Crystallinity affects polymer properties.
Physical Transitions in Polymers
- Amorphous polymers have a glass transition temperature (Tg).
- Crystalline polymers have a melting temperature (Tm).
- Tm and Tg define application limits for polymers.
- Molecular weight, symmetry and bulky structure affect Tg and Tm.
Bulk Side Groups and Molecular Symmetry
- Bulky side groups increase Tg.
- Molecular symmetry tends to decrease Tg.
Other
- ASTM International Resin Identification Codes help classify and identify different plastic types.
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Description
Test your knowledge on various materials used in food packaging, including polymers, paper, glass, and plastics. This quiz covers concepts such as Modified Atmosphere Packaging, aseptic packaging, and the properties of different types of polymers. Challenge yourself and learn more about the science of food packaging!
