Polymer Classifications: HDPE, LDPE, Thermosets

Polymer Classifications

• Polymers are classified by origin, polymerization, molecular force, structure, monomers, backbone chain, and crystallinity/microstructure.

Polymer Classifications Based on Origin

• Polymers are classified as natural/biological, synthetic, or semisynthetic based on origin

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

• HDPE features mostly linear molecules packed closely together
• HDPE is suitable for products like milk jugs, bottle caps, toys, and soap bottles
• LDPE is more branched and used for plastic bags, electric wire insulation and newspaper bags

Thermoplastic Polymers vs. Thermoset Polymers

• Thermoplastic polymers soften when heated and can be repeatedly melted and cooled to form new shapes
• Thermoplastic polymers can be reshaped, remolded, and recycled
• Thermoset polymers discolor and decompose instead of softening upon heating
• Thermoset polymers are rigid plastics that cannot be reshaped or recycled once formed, and are more resistant to heat and chemicals

Types of Resins

• Common resin types include Alkyd, Phenolic (Phenol formaldehyde), Epoxy (Epoxide groups), Polyurethane, Polyester (saturated or unsaturated), Vinyl ester, Acrylic (Methacrylic group), and BMI (Bisamaleimids) resins.

Applications of Resin

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

Resin Curing with UV Light

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

Polymer Fiber Definition & Types

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

Crystalline, Amorphous, and Semi-Crystalline Polymers

• Crystalline polymers have molecules lined up neatly, forming strong, rigid, and non-transparent fibers
• Amorphous polymers have randomly tangled molecules, making them soft, rubbery, and transparent
• Semi-crystalline polymers combine crystalline and amorphous regions; most crystalline polymers are semi-crystalline

Glass Transition Temperature (Tg) & Polymers

• Tg is the glass transition temperature, a characteristic property of each polymer
• Above Tg, the polymer is rubbery and tough; below Tg; it is glass-like, hard, stiff, and brittle
• Knowing Tg is important for applications like tire manufacturing, ensuring they remain tough and elastic

Chewing Gum and Glass Transition Temperature

• Chewing gum demonstrates the glass transition temperature property
• Chewing gum is rubbery and tough at warmer temperatures
• Chewing gum becomes glass-like, hard, and brittle when chilled

Recycling Process & Importance

• Recycling involves melting easily recyclable resins into their original form for reuse
• Recycling reduces pollution, protecting wildlife and humans from microplastics

Disposing of Plastics

• Plastics can be disposed of in landfills, through incineration, biodegradation, or recycling
• Challenges include slow decomposition in landfills and toxic gas release during incineration so environmentally friendly plastics are a solution
• Recycling involves chopping, melting, or remolding plastics

Plastic Bottle Disposal Scenarios

• Scenario 1: Bottles in landfills can leach toxic compounds into soil and harm wildlife
• Scenario 2: Bottles floating in the ocean end up in the Great Pacific Garbage Patch, harming marine life; small fish eat the plastics
• Scenario 3: Bottles are recycled, compressed, shredded, washed, melted, and reused, promoting a better environment

Types of Polymers Based on Structure

• Main polymer structures are linear, branched, cross-linked, and networked
• Linear polymers feature long chains of monomers with no branches
• Branched polymers have shorter monomer chains branching off the main chain
• Cross-linked polymers are linear chains linked by covalent bonds of smaller molecules
• Networked polymers have mer units with three active covalent bonds

Teflon Properties

• Teflon's properties include heat resistance at high and low temperatures, low friction, non-stickiness and non-wetting
• Teflon has electrical properties, abrasion resistance, and chemical resistance

Teflon Resistance

• Teflon (PTFE) is resistant because of its unique carbon and fluorine atom composition
• The strong bond makes it resistant to chemicals, heat, and environmental conditions

Byproducts of Condensation Polymerization

• Condensation polymerization produces water, alcohol, ammonia, and HCl as byproducts
• Removing these byproducts breaks equilibrium, increasing polymer production via Le Chatelier's principle

Conductive Polymers

• Conductive polymers are semi-conductive and can conduct electricity
• Polyacetylene was the first conductive organic polymer discovered

Conductive Polymer Applications

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

Advantages of Conductive Polymers

• Conductive polymers are less expensive, flexible, lightweight, and simple to fabricate
• Conductive polymers have tunable optoelectronic and physical properties

Vulcanization

• Vulcanization is the process of cross-linking natural rubber with sulfur
• Vulcanization makes the rubber harder, more durable, and elastic
• Charles Goodyear discovered vulcanization

Natural Rubber vs. Gutta Percha

• Natural rubber has flexible chains and weak intermolecular forces, displaying elastic properties.
• Gutta-percha has zigzag chains that fit together, is non-elastic, and crystalline
• Both are 1,4-isoprene but natural rubber is the cis formation and gutta percha is the trans formation

Cis vs. Trans Polyisoprene

• Cis polyisoprene is available in over 200 latexes, is produced at higher rates than plants, and is the main source of natural rubber from the rubber tree Hevea Brasiliense
• Cis Polyisoprene properties are that it features a high yield and high mechanical properties
• Trans polyisoprene includes balata and Gutta-percha
• Trans polyisoprene is known for rigidity, low thermal expansion and resistance to acids & alkalis.

Arrangements of Heteropolymers/Copolymers

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

Semi-Synthetic Polymers

• Cellulose nitrate is used for vinyl records, and cellulose acetate is used for film

Hydrogels

• Hydrogels are 3D hydrophilic crosslinked polymeric networks with high water absorption
• Hydrogels can absorb 10x-100x their mass in water
• Hydrogels are used for drug delivery, contact lenses, Band-Aids, diapers, and tissue engineering

Common Synthetic Polymer Types

• Polyethylene is the most common synthetic polymer
• The two types of polyethylene are high-density (HDPE) and low-density (LDPE)
• HDPE has linear molecules that pack tightly, making it strong and rigid, used for bottle caps and toys
• LDPE has branched molecules, used for plastic bags, electric wire insulation, and plastic

Recycling Symbol Numbers

• The number inside the recycling symbol indicates the plastic type and recyclability
• Number 2 is HDPE, which is recycled faster and more often than number 4, LDPE

Fiber Types

• The two types of fibers are natural and synthetic
• Natural fibers come from animals and plants
• Synthetic fibers are man-made

Viscosity

• Viscosity measures a fluid's resistance to flow, corresponding to "thickness" in liquids
• Low viscosity fluids flow easily due to little molecular friction

Incinerating Plastics Disadvantage

• Incinerating plastics releases toxic fumes, like HCl from burning PVC

Organic vs. Inorganic Polymers

• Organic polymers have a carbon molecule backbone, making them purer
• Inorganic polymers have various elements besides carbon

Fillers vs. Additives in Polymers

• Filler polymers add weight or reduce cost
• Additive polymers add a specific property

Polymerization Forms

• Two forms of polymerization exist: addition and condensation
• Addition polymerization involves monomers adding without losing atoms (PE, PP, PVC, PS, Teflon)
• Condensation polymerization involves byproducts (nylon, polyester, PET)

Transparent Polymers

• Amorphous polymers are the only transparent polymers
• Amorphous polymers features unorganized molecules, are soft and rubbery, with low support for other molecules

Organized Polymers

• Crystalline polymers have molecules lined up in lamellae, making them strong and heat-resistant

Viscose, Elasticity, and Viscoelasticity

• Viscose describes flow in a fluid, like water
• Elasticity is an object's ability to return to its original shape after deformation, more rigid
• Viscoelasticity blends viscosity and elasticity, material returns to it's original shape even with higher density

Polymer Mixture Types

• Polymer mixtures can be immiscible, miscible, or partially miscible
• Immiscible: multiphase with no mixture of components
• Miscible: single-phase, completely soluble
• Partially miscible: multiphase with some mixing

Composite Polymer Material

• Composite polymer materials are made from two or more constituent materials with two phases
• The matrix phase is the polymer, while the disperse phase includes plasticizers, fibers, ceramic and metal particles

Polymer Classifications in Nature

• Classifications of polymers occurring in nature: Polysaccharides, Proteins, Polynucleotides, Polyisoprenes, Polyesters

Cellulose Sources

• Cellulose can be found in wood, cotton, hemp, linen, and jute

Cellulose vs. Starch Structure

• Both cellulose and starch have that comprise glucose monomer units
• Cellulose has strong β-linkage, while starch has a weaker α-linkage
• Starch is digestible by humans; cellulose is not

Cellulose Definition & Applications

• Cellulose is the main component of plant cell walls
• Cellulose makes up about half the biomass of photosynthetic organisms
• It is used in veterinary foods, pulp/paper, fibers/clothes, cosmetics, and pharmaceuticals

Matrix and Disperse Identification

• The matrix is the long polymer chain polymer
• The disperse are particles, not long chains

Lignin Definition and Roles

• Lignin is the most abundant aromatic polymer in nature
• Lignin's roles are hydrophobic, found in plant cell walls to provides biomechanical strength, rigidity and support for plants and upright growth

Lignin Applications

• Lignin applications: nonfermentable boiling fuel, adhesives, polymers polyols, sizing, coating/emulsifier agent, and flame retardant (nano lignin)

Pectin Definition and Applications

• Pectin is a polysaccharide starch in fruit cell walls, high in citrus rinds and apples
• Pectin is a gelling agent and thickener for jams and stabilizes acidic protein drinks
• Pectin can be applied in medicine to increase stool viscosity for constipation and diarrhea and reduce lipoprotein and cholesterol levels

Pectin Changes During Fruit Ripening

• Pectin is insoluble in immature fruit cell walls
• Pectin becomes soluble as fruit ripens, aiding consumption
• Pectin breaks down when fruit is overripe, becoming water-soluble (fruit softens)

Mucilage Gums

• Mucilage gums are natural blends of several gums or polysaccharides with high viscosity
• Mucilage gums have their extraction from seeds, soft stems, leaves, middle lamella, barks and roots
• They are used in food products due to functional and bioactive properties

Protein Synthesis

• Plants synthesize proteins from carbon dioxide, water, and minerals such as nitrates or sulfates
• Animals must consume proteins
• Humans can synthesize some amino acids but need essential ones from diet

Forms of Casein

• Casein exists as micellar and protein salts (calcium caseinate and sodium caseinate)
• Micellar casein is purer and rich in calcium and phosphorous
• Casein salts have less clotting and are cheaper

Casein for Diet Programs

• Casein protein is digested slower than others, reducing appetite and increasing fullness

Protein Structures

• Proteins have four structures: primary, secondary, tertiary, and quaternary
• Primary structure details the amino acid sequence from N-terminal to C-terminal.
• Secondary structure relates to polypeptide chain folds due to hydrogen bonding.
• Tertiary structure refers to spatial relationships of groups far apart on the protein chain.

Protein Classification

• Proteins are classified by shape, size, solubility, composition, or function
• Globular proteins are spherical, water-soluble, and fragile (antibodies, enzymes, hormones)
• Fibrous proteins are tougher, water-insoluble, structural tissues (hair, nails, skin)
• Simple proteins produce only amino acids when hydrolyzed (albumin)
• Compound proteins (conjugated) combine simple proteins and prosthetic groups
• Derived proteins result from hydrolysis of simple or conjugate proteins

Gelatin Types

• Type A gelatin is from acid hydrolysis
• Type B is from basic (alkali) hydrolysis.
• Type A is found in porcine skin, and Type B in bovine skin.

Gums

• Gums are non-starch, water-soluble polysaccharides. Gums possess an ability to thicken water
• Different gum categories: exudate, microbial and mucilage

Gelatin Derivation

• Gelatin is a partially hydrolyzed form of collagen. Irreversible hydrolysis unfolds the alpha triple helix structure by partially breaking some of the hydrogen bonds between the inter wound polypeptide
• It is extracted from animal (pigs and cows) tissues via thermal hydrolysis (acid or alkaline)
• Growing interests involves extracting gelatin from the scales of fish and insects instead of mammals.

Exudate Gums Vs. Microbial Gums

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

Starch Composition

• Starch has two polymers: amylose and amylopectin
• Amylose is a water-soluble α-D linked polyglucan
• Amylopectin is more susceptible to hydrolysis

Starch Types based on Source

• Plant starch includes amylose and amylopectin
• Animal starch is glycogen

Soy Protein

• Soy proteins are globular, plant-based and are tangled into a 3D structure by disulfide and hydrogen bonds
• In food or biomedical industries

Alpha vs. Beta-Keratin

• Alpha-keratins are found in humans and mammal wool
• Beta-keratins are polypeptide chains found in birds and reptiles which can possess possess alpha-keratins

Natural Poly Esters

• Four types that exist are: Cutin, Suberin, Polyhydroxyalkanoates (PHA) and Poly 𝛼-esters
• Cutin is a waxy substance in plant cuticles for water repellency
• Suberin is similar to cutin and used for cork.
• Polyhydroxyalkanoates that are derived from bacterial fermentation
• Poly 𝛼-esters are medical grade type polyesters

General Characteristics of PHA

• Several characteristics exist: water insoluble, hydrolytic degradation resistant and good UV resistance
• PHA is soluble in chloroform, biocompatible, sinks in water, and is nontoxic
• PHA is less 'sticky' than traditional polymers when melted, and are used in tissue engineering

Biodegradation vs. Composting

• Biodegradation is a naturally happening and naturally-occurring breakdown of organic substances such as bacteria or fungi
• Composting is a human-driven breakdown
• Natural polymers are usually biodegradable

Biocompatibility

• Biocompatibility is compatibility with a living systems or tissue by not being toxic
• Soy protein and silk fibroin are examples

Hyaluronic Acid

• Hyaluronic acid or hyaluronate is a glycoprotein (oligosaccharide + protein)/mucopolysaccharide, is gooey, and its water bound
• It can be from bovine vitreous humor, rooster combs, and streptococcus zooepidemicus

Ways to Link Protein Chains

• Protein chains are linked by hydrogen bonds, ionic bonds, disulfide linkages, and dispersion forces
• Hydrogen bonds occur between amide nitrogen and carboxyl oxygen in secondary structures

Zein

• Zein is a corn processing byproduct that is hydrophobic, biodegradable prolamin and alcohols are used
• Zein is soluble in alcohols (ethanol, isopropanol), and is used in food packaging, films/coatings, plastics

Chitosan vs. Chitin

• Chitin is a hydrophobic polysaccharide of invertebrate exoskeletons
• Chitin is insoluble but is positively charged, resulting in antibacterial activity
• Chitosan is a deacetylated chitin more desirable as a means for drug delivery and is also antibacterial
• Applications for chitosan are that it is due to its solubility in acidic solutions

Chitin vs. Cellulose

• Chitin is like cellulose
• Chitin's hydroxyl groups in cellulose are substituted by an acetamido group

Poly Lactic Acid

• Poly lactic acid is a natural polymer made from lactic acid
• It can be used in textile, agriculture, packaging and biomedical industries