Polymer Classifications: HDPE, LDPE, Thermosets

Classifications of Polymers

• Polymers can be classified by origin, polymerization, molecular force, structure, monomers, backbone chain, and crystallinity (microstructure).
• Based on origin, polymers are classified as natural/biological, synthetic, or semisynthetic.

High Density Polyethylene (HDPE) vs. Low-Density Polyethylene (LDPE)

• HDPE is composed of mostly linear molecules that pack closely together.
• HDPE is used in milk jugs, bottle caps, toys, and soap bottles.
• LDPE is a more highly branched form of polyethylene.
• LDPE is used in plastic bags, electric wire insulation, and newspaper bags.

Thermoplastic vs. Thermoset Polymers

• Thermoplastic polymers soften when heated and can be repeatedly melted and cooled to form new shapes, allowing them to be reshaped, remolded, and recycled.
• Thermoset polymers do not soften upon heating but discolor and decompose; they are rigid plastics that cannot be reshaped or recycled once formed.
• Thermoset polymers are more resistant to heat and chemicals compared to thermoplastics.

Types of Resins

• Examples of resins include Alkyd Resins, Phenolic Resin (Phenol formaldehyde), Epoxy Resins (Epoxide groups), Polyurethane Resins, Polyester Resins (saturated or unsaturated), Vinyl ester Resins, Acrylic Resins (Methacrylic group), and BMI Resins (Bisamaleimids).

Resin Applications

• Resins are used in surface coatings, paints, printing inks, electrical insulation, medical applications, adhesives, industrial and decorative laminates, structural composites, ion exchange resins, and 3D printing.

Resin Curing

• Resins require photoinitiators to kick-start the polymerization process when cured by UV light.

Polymer Fiber Definition

• A polymer is converted into fiber if drawn into a long filament with a length at least 100 times its diameter.
• Natural fibers include wool, cashmere & mohair, camel hair, angora wool, alpaca & lama hair, silk fibers, cotton seed pods, coir, linen, manila or sisal, jute stem fibers, and fiberglass.
• Synthetic fibers include PE & PP fibers, nylon, acrylic, and polyester.

Crystalline, Amorphous, and Semi-Crystalline Polymers

• Crystalline polymers have molecules that line up in a neat row, forming fibers with great strength; they tend to be rigid and non-transparent.
• Amorphous polymers have molecules that are randomly tangled; they tend to be soft, rubbery, and transparent.
• Semi-crystalline polymers combine crystalline and amorphous structure regions; most crystalline polymers are semi-crystalline.

Glass Transition Temperature (Tg)

• Tg is a property of polymers indicating the glass transition temperature, which is characteristic for each polymer.
• Above the Tg, a polymer is rubbery and tough; below the Tg, it is glass-like, hard, stiff, and brittle.
• Knowing the Tg helps in applications like tire manufacturing, ensuring toughness and elasticity.

"Glass Transition Temperature" property of Chewing Gum

• Chewing gum is rubbery and tough at warmer temperatures.
• Chewing gum becomes glass-like, hard, and brittle when chilled.

Recycling

• Easily recyclable resins are melted down to their original form and reused.
• Recycling reduces pollution and harm to wildlife and humans caused by microplastics.

Disposing of Plastics

• Unwanted plastic waste can be disposed of in landfills, incinerated, biodegraded, or recycled.
• Landfills pose an issue due to the long decomposition time of plastics.
• Incineration of plastics can release toxic gases affecting the ozone layer.
• Alternatives include producing biodegradable and photodegradable plastics or recycling, which involves chopping, melting, or remolding plastics.

Scenarios for Disposed Plastic Bottles

• Scenario 1: Bottles in landfills can lead to water flowing through waste, absorbing toxic compounds, creating leachate that harms soil and wildlife.
• Scenario 2: Bottles floating in oceans end up in the Great Pacific Garbage Patch, affecting sea life as small fish eat the plastics, which go up the food chain to humans.
• Scenario 3: Recycling compresses, shreds, washes, melts, and reuses the plastic, promoting an eco-friendly environment with less waste.

Polymer Structure Types

• Main polymer types based on structure are linear, branched, cross-linked, and network.
• Linear polymers have long chains of monomers with no branches or cross-links.
• Branched polymers have shorter monomer chains branching off the main chain.
• Cross-linked polymers are linear chains joined by covalent bonding of smaller molecules.
• Networked polymers feature mer units with three active covalent bonds, forming interconnected 3D network configurations and highly crosslinked polymers.

Teflon Properties

• Teflon's main properties include heat resistance against high and low temperatures, low friction, nonstick, non-wetting, electrical properties, abrasion resistance, and chemical resistance.

Teflon Resistance

• Teflon's chemical composition with carbon and fluorine atoms creates a strong bond, making it resistant to chemicals, heat, and environmental conditions.

Condensation Polymerization Byproducts

• Water, alcohol, ammonia, and HCl are the byproducts of condensation polymerization.
• Removing polymer byproducts breaks the equilibrium, which produces more polymer to restore equilibrium, increasing efficiency.

Conductive Polymers

• Conductive polymers have semi-conductive properties, allowing them to conduct electricity.
• Polyacetylene was the first conductive organic polymer discovered.

Conductive Polymer Applications

• Conductive polymers are used in drug delivery, photovoltaic cells, plastic batteries, display devices, microelectronics, chemically modified electrodes, corrosion protection, and polymer light-emitting diodes (PLED).

Conductive vs. Non-Conductive Polymers

• Conductive polymers are less expensive, flexible, lightweight, and allow for simple and inexpensive fabrication with tunable optoelectronic and physical properties compared to non-conductive polymers.

Vulcanization

• Vulcanization is the process of reacting natural rubber with sulfur to cross-link the chains, making the rubber harder, more durable, and elastic; Charles Goodyear discovered this process.

Natural Rubber vs. Gutta Percha

• Natural rubber has long flexible chains, weak intermolecular forces, and exhibits elastic properties.
• Gutta-percha has zigzag chains fitting together, making it non-elastic and crystalline.
• Both are 1,4-isoprene, but natural rubber is the cis formation, while gutta-percha is the trans formation.

Cis Polyisoprene vs. Trans Polyisoprene

• Cis polyisoprene is widely available in over 200 latexes and produces higher yields in plants. Hevea Brasiliense is its main commercial source.
• Cis polyisoprene properties include high yield and high mechanical properties.
• Trans polyisoprene includes balata and Gutta-percha and exhibits rigidity, extremely low coefficient of thermal expansion/contraction, and alkali and acid resistance.

Heteropolymers/Copolymers Arrangements

• Heteropolymers/copolymers can have random, alternating, block, graft, and star arrangements.

Semi-Synthetic Polymers

• Cellulose nitrate is used for making vinyl records.
• Cellulose acetate is used for making film.

Hydrogels

• A hydrogel is a 3D hydrophilic crosslinked polymeric network that has high water absorption, absorbing 10x-100x times more than its mass.
• Applications include drug delivery, contact lenses, Band-Aids, diapers, and tissue engineering.

Synthetic Polymer type - Polyethylene

• Polyethylene is the most common synthetic polymer.
• Types: High Density (HDPE) and Low Density (LDPE).
• HDPE has linear molecules that pack tightly making it rigid. It is used in bottle caps and toys.
• LDPE has branched molecules, used to make plastic bags and electric wire insulation.

Recycling Symbol Numbers

• The number inside the recycling symbol indicates the type of plastic and its recyclability; for example, 2 is HDPE and is more easily recycled than 4, which is LDPE.

Types of Fibers

• Natural fibers are sourced from animals and plants, while synthetic fibers are man-made.

Viscosity

• Viscosity measures a fluid's resistance to flow.
• Low viscosity fluids flow easily due to low molecular friction.

Incinerating Plastics

• Incinerating plastics releases toxic fumes.
• Burning PVC releases HCl when burned.

Organic vs. Inorganic Polymers

• Organic polymers are associated with a carbon molecule backbone, making them purer.
• Inorganic polymers have various different elements other than just carbon.

Fillers vs. Additives in Polymers

• Fillers add weight or reduce cost.
• Additives add a property to the polymer.

Polymerization Forms

• Addition polymerization is when monomers add to one another without losing any atoms (e.g., PE, PP, PVC, PS, Teflon).
• Condensation polymerization creates byproducts when two molecules react chemically (e.g., nylon, polyester, PET).

Transparent Polymers

• Transparent polymers are known as amorphous polymers.
• These are unorganized molecules that may be tangled and random, soft and rubbery, with low support for other molecules.

Organized Polymers

• Crystalline polymers are organized with molecules aligned in rows called lamellae, making them strong and heat-resistant with a high melting point.

Viscose, Elasticity, and Viscoelasticity

• Viscose is a fluid's ability to flow (e.g., water).
• Elasticity is an object's ability to return to its original shape (e.g., cheese wheel).
• Viscoelasticity combines viscosity and elasticity, allowing an object to resume its shape with a thick consistency (e.g., pizza dough).

Polymer Mixtures

• Immiscible mixtures have no mixture between components.
• Miscible mixtures are single-phase, completely soluble and cannot be seen.
• Partially miscible mixtures are multiphase with some mixing.

Composite Polymer Material

• A composite material is a polymer produced from two or more constituent materials with two phases: matrix and disperse.
• The matrix phase is the polymer, while the disperse phase can be plasticizers, fibers, ceramic, and metal particles.

Main Classifications of Natural Polymers

• Natural polymers include polysaccharides, proteins, polynucleotides, polyisoprenes, and polyesters.

Cellulose Sources

• Wood, cotton, hemp, linen, and jute are sources of cellulose.

Cellulose Structure vs. Starch

• Cellulose and starch are composed of glucose monomer units.
• Cellulose has a strong β-linkage, while starch has a weaker α-linkage.
• Starch is more digestible due to the α-linkage; humans cannot digest polysaccharides with β-linkage.

Cellulose

• Cellulose is the principal component of plant cell walls, making up about half of photosynthetic organisms' biomass.
• Applications of cellulose are veterinary foods, pulp and paper, fibers and clothes, cosmetic, and pharmaceutical industries.

Lignin

• Lignin is the most abundant aromatic polymer (heteropolymer) in nature.
• Lignin is a hydrophobic polymer in plant cell walls, providing the matrix that binds cellulose microfibrils.
• Lignin provides biomechanical strength, rigidity, and support, and prevents penetration of destructive enzymes and supports upright growth.
• Lignin applications include nonfermentable boiling fuel, adhesives, polymers polyols, sizing, coating and emulsifier agent, and flame retardants.

Pectin

• Pectin is a polysaccharide starch found in fruit cell walls, particularly in citrus rinds and apples.
• Pectin is a gelling agent and thickener for jams, stabilizes acidic protein drinks, increases stool viscosity, activates cell death pathways, reduces cholesterol levels, and is used as a vegetable glue substitute.

Pectin in Ripening Fruit

• Pectin is insoluble in immature fruits but becomes soluble as fruit ripens.
• Overripe fruit has pectin broken down into simple sugars, causing it to soften and lose its shape.

Mucilage Gums

• Mucilage gums are a natural blend of gums or polysaccharides extracted from seeds, stems, leaves, barks, and roots.
• Their utilization is increasing due to their functional and bioactive properties.

Protein Synthesis

• Plants synthesize proteins from carbon dioxide, water, and minerals like nitrates or sulfates.
• Animals must consume proteins; humans can synthesize some amino acids but need essential amino acids from their diet.

Casein

• Casein exists in micellar and protein salt forms.
• Micellar casein is the purest and rich in calcium and phosphorous.
• Casein salts have less clotting properties and are cheaper.

Benefits of Casein

• Casein is digested more slowly, reducing appetite and increasing feelings of fullness.

Protein Primary Structure

• The primary structure is the amino acid sequence from N-terminal to C-terminal.

Protein Secondary Structure

• Secondary structure involves polypeptide chain folds and coils due to hydrogen bonding of amide groups, with α-helix and β-pleated sheets as examples.

Protein Tertiary Structure

• Tertiary structure is the three-dimensional shape of a protein due to spatial relationships of groups far apart, with the protein chain in globular proteins as an example.

Protein Quaternary Structure

• Quaternary structure involves the interaction of more than one peptide chain.

Protein Classifications

• Proteins can be classified by shape, size, solubility, composition, and function.
• Based on shape and size, proteins are Globular and Fibrous. Globular proteins are spherical shape and are water soluble types which are rather fragile in nature; Antibodies, enzymes, and hormones are typical examples. Fibrous proteins: Fibrous shape and are tougher water insoluble proteins such as hair, nails, and skin.
• Proteins can be classified based on composition and solubility as simple, compound, and derived proteins. Simple proteins produce amino acids only such as albumin when hydrolyzed. Compound proteins: also known as conjugate proteins is a combination of simple proteins and prosthetic (non-protein) groups like Lipoproteins. Derived proteins are proteins derived from complete or partial acidic, alkali or enzymatic hydrolysis of simple or conjugate proteins like Metaproteins or peptides.
• Proteins are classified based on their functions as catalytic (such as enzymes), protective (such as antibodies), regulatory (such as hormones), storage, transport, toxic, exotic, contractile, secretary, and structural proteins.

Gelatin Types

• Type A gelatin is obtained through acid hydrolysis and is found in Porcine skin.
• Type B is obtained through basic (alkali) hydrolysis and is found in Bovine skin.

Gums

• Gums are non-starch, water-soluble polysaccharides with commercial importance, capable of thickening water and aqueous systems.
• Types of gums: exudate, microbial and mucilage gums.

Gelatin Derivation

• Gelatin is a partially hydrolyzed form of collagen derived from tissues like bones and skins of mammals (pigs and cows) through thermal hydrolysis using acid or alkaline.
• Alternative sources are fish scales and insects.

Exudate vs. Microbial Gums

• Exudate gums are polysaccharides produced by plants due to stress, such as gum arabic, gum tragacanth, gum karaya, and gum ghatti.
• Microbial gums are polysaccharides produced by bacteria, such as xanthan gum, pullulan, gellan gum, wellan gum, and rhamsan gum.

Starch

• Starch is composed of amylose and amylopectin.
• Amylose is a water-soluble polysaccharide made of (1-4)-a-D linked polyglucan.
• Amylopectin branching occurs after every 28–30 glucose units, is more susceptible to hydrolysis and degradation. Starch is generally insoluble in water and alcohol.

Starch Types

• Plant starch includes amylose and amylopectin, while animal starch is glycogen.

Soy Protein

• Soy proteins are globular and plant-based, entangled into a three-dimensional structure by disulfide and hydrogen bonds.
• Applications include soy beverages, meat alternatives, nutrition bars, cereals, animal feed, tissue regeneration, drug delivery, and wound dressings.

Alpha-Keratin vs. Beta-Keratin

• Alpha-keratins are found in humans and the wool of mammals.
• Beta-keratins are categorized as polypeptide chains and are only found in birds and reptiles; however, those species can also possess alpha-keratins.

Natural Poly Esters

• Types: Cutin, Suberin, Polyhydroxyalkanoates (PHA), Poly α-esters.
• Cutin is a waxy, water-repellent substance in the cuticle of plants to protect against water loss.
• Suberin is synthesized within mainly root tissue, similar to Cutin, and is the main constituent of cork.
• Polyhydroxyalkanoates are natural polyesters derived from bacterial fermentation.
• Medical grade polyesters are Poly α-esters which lactic acid is the most famous one among them.

Polyhydroxyalkanoates (PHA)

• PHA is water insoluble, relatively resistant to hydrolytic degradation, and has good ultraviolet resistance but poor resistance to acids and bases.
• PHA is soluble in chloroform and chlorinated hydrocarbons, biocompatible, sinks in water, non-toxic, and less 'sticky' than traditional polymers when melted.
• Applications include tissue engineering, drug delivery systems, and bio compact and biodegradable plastics.

Biodegradation vs. Composting

• Biodegradation is the naturally-occurring breakdown of organic matter by microorganisms.
• Composting is a human-driven process of biodegradation under specific conditions.
• Natural polymers are biodegradable.

Biocompatibility

• Biocompatibility is the ability of a material to be compatible with living tissue or systems without toxicity, injury, or rejection.
• Silk fibroin and soy protein are examples of biocompatible polymers.

Hyaluronic Acid

• Hyaluronic acid, also known as hyaluronan or hyaluronate, is a glycoprotein (oligosaccharide + protein) also known as mucopolysaccharides
• It is a gooey, slippery, natural substance in the body.
• Main sources are cord bovine vitreous humor, rooster combs, and bacteria streptococcus zooepidemicus.

Protein Chain Links

• Protein chains can be linked by hydrogen bonds, ionic bonds, disulfide linkages, and dispersion forces.
• Hydrogen Bond: Hydrogen bonds are formed between amide nitrogen (N-H) and carboxyl oxygen (C=O).
• Ionic Bonds also known as salt bridges occur between oppositely charged side chains.
• Disulfide Linkages: When two cysteine side chains are oxidized, a (-S-S-) disulfide linkage can form.
• Dispersion Forces: These molecules are attractive forces between two nonpolar side chains.

Zein

• Zein is a biodegradable, hydrophobic prolamin protein by-product of corn processing.
• Applications include films and coatings in food packaging, biodegradable plastics, fibers, and chewing gum.

Chitosan vs Chitin

• Chitin is a hydrophobic linear polysaccharide from the exoskeleton of invertebrates, fungi, and bacteria, insoluble in water but soluble in organic solvents.
• Chitosan is deacetylated chitin, more desirable for drug delivery due to free amino groups, and exhibits antibacterial properties.
• Chitosan is soluble in acidic solutions.