\section{Macromolecule and Plastics}

Macromolecules, also known as polymers, are large molecules composed of repeating structural units (monomers) connected by covalent bonds. Synthetic polymers (plastics) have become ubiquitous materials in modern life due to their versatility, durability, and low cost.

\subsection{Addition polymers}

Addition polymers are formed by the repeated addition of monomers containing double bonds without the loss of any atoms. The reaction is called addition polymerization or chain-growth polymerization.

\vspace{0.5cm}

\textbf{Polyethylene (PE)}

\textbf{Monomer:} Ethylene (ethene): \chemfig{CH_2=[:30]CH_2}

\textbf{Chemical formula:} \ce{(C2H4)n} or \ce{(-CH2-CH2-)n}

\textbf{Reaction type:} Addition polymerization (free radical, Ziegler-Natta, or metallocene catalysis)

\textbf{Polymerization reaction:} 

\ce{n CH2=CH2 ->[catalyst, heat, pressure] (-CH2-CH2-)n}

\textbf{Structure:} \chemfig{-[:30](-[:90]H)(-[:270]H)-[:330](-[:30]H)(-[:270]H)-[:30](-[:90]H)(-[:270]H)-[:330](-[:30]H)(-[:270]H)-[:30]}

\textbf{Types:}
\begin{itemize}
\item LDPE (Low-density polyethylene): Branched chains, flexible, transparent
\item HDPE (High-density polyethylene): Linear chains, rigid, opaque
\item UHMWPE (Ultra-high molecular weight PE): Extremely long chains, very strong
\end{itemize}

\textbf{Properties:}
\begin{itemize}
\item Chemically inert, resistant to acids and bases
\item Excellent electrical insulator
\item Lightweight and flexible (LDPE) or rigid (HDPE)
\item Water-resistant
\item Recyclable (recycling code 2 for HDPE, 4 for LDPE)
\end{itemize}

\textbf{Usage:} Plastic bags, bottles, containers, toys, electrical insulation, pipes, packaging films

\vspace{0.5cm}

\textbf{Polypropylene (PP)}

\textbf{Monomer:} Propylene (propene): \chemfig{CH_2=[:30]CH-[:330]CH_3}

\textbf{Chemical formula:} \ce{(C3H6)n} or \ce{(-CH2-CH(CH3)-)n}

\textbf{Reaction type:} Addition polymerization (Ziegler-Natta catalysis)

\textbf{Polymerization reaction:} 

\ce{n CH2=CH-CH3 ->[catalyst] (-CH2-CH(CH3)-)n}

\textbf{Structure:} \chemfig{-[:30](-[:90]H)(-[:270]H)-[:330](-[:30]H)(-[:270]CH_3)-[:30](-[:90]H)(-[:270]H)-[:330](-[:30]H)(-[:270]CH_3)-[:30]}

\textbf{Properties:}
\begin{itemize}
\item Higher melting point than polyethylene (160-170°C)
\item Good chemical resistance
\item Strong and rigid
\item Good fatigue resistance
\item Lightweight
\item Recyclable (recycling code 5)
\end{itemize}

\textbf{Usage:} Automotive parts, packaging, textiles (fibers and fabrics), food containers, bottle caps, medical equipment, living hinges

\vspace{0.5cm}

\textbf{Polyvinyl chloride (PVC)}

\textbf{Monomer:} Vinyl chloride: \chemfig{CH_2=[:30]CH-[:330]Cl}

\textbf{Chemical formula:} \ce{(C2H3Cl)n} or \ce{(-CH2-CHCl-)n}

\textbf{Reaction type:} Addition polymerization (free radical polymerization)

\textbf{Polymerization reaction:} 

\ce{n CH2=CHCl ->[initiator] (-CH2-CHCl-)n}

\textbf{Structure:} \chemfig{-[:30](-[:90]H)(-[:270]H)-[:330](-[:30]H)(-[:270]Cl)-[:30](-[:90]H)(-[:270]H)-[:330](-[:30]H)(-[:270]Cl)-[:30]}

\textbf{Properties:}
\begin{itemize}
\item Rigid and hard in pure form
\item Can be plasticized to become flexible
\item Excellent chemical resistance
\item Good electrical insulator
\item Flame retardant (due to chlorine content)
\item Durable and weather-resistant
\item Recyclable (recycling code 3)
\end{itemize}

\textbf{Usage:} Water pipes, electrical cable insulation, window frames, flooring, credit cards, medical tubing, inflatable products

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\textbf{Polystyrene (PS)}

\textbf{Monomer:} Styrene: \chemfig{CH_2=[:30]CH-[:330]*6(=-=-=-)}

\textbf{Chemical formula:} \ce{(C8H8)n} or \ce{(-CH2-CH(C6H5)-)n}

\textbf{Reaction type:} Addition polymerization (free radical polymerization)

\textbf{Polymerization reaction:} 

\ce{n CH2=CH-C6H5 ->[initiator] (-CH2-CH(C6H5)-)n}

\textbf{Properties:}
\begin{itemize}
\item Transparent and rigid in pure form
\item Brittle at room temperature
\item Low melting point (240°C)
\item Good electrical insulator
\item Can be expanded into foam (EPS - expanded polystyrene)
\item Recyclable (recycling code 6)
\end{itemize}

\textbf{Usage:} Packaging (foam peanuts, egg cartons), disposable cups and plates, insulation, CD/DVD cases, model building

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\textbf{Polytetrafluoroethylene (PTFE, Teflon)}

\textbf{Monomer:} Tetrafluoroethylene: \chemfig{F-[:30]C(-[:90]F)=[:330]C(-[:270]F)-[:30]F}

\textbf{Chemical formula:} \ce{(C2F4)n} or \ce{(-CF2-CF2-)n}

\textbf{Reaction type:} Addition polymerization (free radical polymerization under pressure)

\textbf{Polymerization reaction:} 

\ce{n CF2=CF2 ->[initiator, pressure] (-CF2-CF2-)n}

\textbf{Structure:} \chemfig{-[:30](-[:90]F)(-[:270]F)-[:330](-[:30]F)(-[:270]F)-[:30](-[:90]F)(-[:270]F)-[:330](-[:30]F)(-[:270]F)-[:30]}

\textbf{Properties:}
\begin{itemize}
\item Extremely low coefficient of friction (non-stick)
\item Chemically inert (resistant to almost all chemicals)
\item High melting point (327°C)
\item Excellent electrical insulator
\item Hydrophobic and oleophobic
\item Very stable at high temperatures
\end{itemize}

\textbf{Usage:} Non-stick cookware coatings, gaskets, seals, chemical-resistant tubing, electrical insulation, medical implants

\vspace{0.5cm}

\textbf{Poly(methyl methacrylate) (PMMA, Acrylic, Plexiglas)}

\textbf{Monomer:} Methyl methacrylate: \chemfig{CH_2=[:30]C(-[:90]CH_3)-[:330]C(=[:270]O)-[:30]O-[:330]CH_3}

\textbf{Chemical formula:} \ce{(C5H8O2)n} or \ce{(-CH2-C(CH3)(COOCH3)-)n}

\textbf{Reaction type:} Addition polymerization (free radical polymerization)

\textbf{Polymerization reaction:} 

\ce{n CH2=C(CH3)COOCH3 ->[initiator] (-CH2-C(CH3)(COOCH3)-)n}

\textbf{Properties:}
\begin{itemize}
\item Optically transparent (92\% light transmission)
\item Scratch-resistant
\item Weather-resistant
\item Shatter-resistant (safer than glass)
\item Good electrical insulator
\item Can be easily molded and shaped when heated
\end{itemize}

\textbf{Usage:} Windows, aquariums, lenses, displays, signs, lighting fixtures, furniture, dental materials

\vspace{0.5cm}

\textbf{Polyacrylonitrile (PAN)}

\textbf{Monomer:} Acrylonitrile: \chemfig{CH_2=[:30]CH-[:330]C~[:30]N}

\textbf{Chemical formula:} \ce{(C3H3N)n} or \ce{(-CH2-CH(CN)-)n}

\textbf{Reaction type:} Addition polymerization (free radical polymerization)

\textbf{Polymerization reaction:} 

\ce{n CH2=CH-CN ->[initiator] (-CH2-CH(CN)-)n}

\textbf{Properties:}
\begin{itemize}
\item Strong and rigid
\item Good chemical resistance
\item Heat-resistant
\item Can be converted to carbon fiber through pyrolysis
\end{itemize}

\textbf{Usage:} Acrylic fibers (clothing, carpets), carbon fiber precursor, outdoor applications, barrier plastics

\subsection{Condensation polymers}

Condensation polymers are formed by the stepwise reaction between monomers with elimination of small molecules (usually water, HCl, or methanol). Also called step-growth polymerization.

\vspace{0.5cm}

\textbf{Nylon (Polyamide)}

\textbf{Common types:} Nylon-6,6 and Nylon-6

\textbf{Monomers (Nylon-6,6):} 
\begin{itemize}
\item Hexamethylenediamine: \chemfig{H_2N-[:0](-[:90])-[:0](-[:270])-[:0](-[:90])-[:0](-[:270])-[:0](-[:90])-[:0]NH_2}
\item Adipic acid: \chemfig{HOOC-[:0](-[:90])-[:0](-[:270])-[:0](-[:90])-[:0]COOH}
\end{itemize}

\textbf{Monomer (Nylon-6):} $\varepsilon$-Caprolactam: \chemfig{*6(-(=[:150]O)-N(-[:330]H)-----)}

\textbf{Chemical formula:} \ce{(-NH-(CH2)6-NH-CO-(CH2)4-CO-)n} (Nylon-6,6) or \ce{(-NH-(CH2)5-CO-)n} (Nylon-6)

\textbf{Reaction type:} Condensation polymerization (polycondensation)

\textbf{Polymerization reaction (Nylon-6,6):}

\ce{n H2N-(CH2)6-NH2 + n HOOC-(CH2)4-COOH -> (-NH-(CH2)6-NH-CO-(CH2)4-CO-)n + 2n H2O}

\textbf{Structure (repeating unit):} \chemfig{-[:30]N(-[:90]H)-[:330]C(=[:270]O)-[:30](-[:90])-[:330](-[:30])-[:330](-[:270])-[:30](-[:90])-[:330]C(=[:30]O)-[:270]N(-[:210]H)-[:330]}

\textbf{Properties:}
\begin{itemize}
\item Strong and durable
\item Good elasticity and abrasion resistance
\item High melting point (250-260°C)
\item Absorbs moisture
\item Can be drawn into strong fibers
\item Forms hydrogen bonds between chains
\end{itemize}

\textbf{Usage:} Textiles and clothing, stockings, carpets, ropes, parachutes, fishing lines, mechanical parts (gears, bearings), toothbrush bristles

\vspace{0.5cm}

\textbf{Polyester (Polyethylene terephthalate, PET)}

\textbf{Monomers:}
\begin{itemize}
\item Ethylene glycol: \chemfig{HO-[:0]CH_2-[:0]CH_2-[:0]OH}
\item Terephthalic acid: \chemfig{HOOC-[:30]*6(=-=-=-)=[:330]COOH}
\end{itemize}

\textbf{Chemical formula:} \ce{(-O-CH2-CH2-O-CO-C6H4-CO-)n}

\textbf{Reaction type:} Condensation polymerization (esterification)

\textbf{Polymerization reaction:}

\ce{n HO-CH2-CH2-OH + n HOOC-C6H4-COOH -> (-O-CH2-CH2-O-CO-C6H4-CO-)n + 2n H2O}

\textbf{Properties:}
\begin{itemize}
\item Strong and lightweight
\item Wrinkle-resistant
\item Quick-drying
\item Transparent (in thin films)
\item Good barrier to gases and moisture
\item Recyclable (recycling code 1)
\end{itemize}

\textbf{Usage:} Beverage bottles, food containers, textiles (polyester fabrics), films, magnetic tape, carpets, upholstery

\vspace{0.5cm}

\textbf{Polycarbonate (PC)}

\textbf{Monomer:} Bisphenol A (BPA) and phosgene (or carbonate precursor)

\textbf{Bisphenol A structure:} \chemfig{HO-[:30]*6(=-=-=-)=[:330]C(-[:30]CH_3)(-[:270]CH_3)-[:330]*6(=-=-=-)=[:270]OH}

\textbf{Chemical formula:} \ce{(-O-C6H4-C(CH3)2-C6H4-O-CO-)n}

\textbf{Reaction type:} Condensation polymerization (interfacial polymerization)

\textbf{Polymerization reaction:}

\ce{n HO-C6H4-C(CH3)2-C6H4-OH + n COCl2 -> (-O-C6H4-C(CH3)2-C6H4-O-CO-)n + 2n HCl}

\textbf{Properties:}
\begin{itemize}
\item Exceptionally high impact resistance
\item Optically transparent
\item Heat-resistant (working temperature up to 120°C)
\item Good electrical insulator
\item Lightweight
\item Can be sterilized
\end{itemize}

\textbf{Usage:} Safety glasses, bulletproof windows, CDs/DVDs, water bottles, medical devices, automotive parts, electronics housings

\vspace{0.5cm}

\textbf{Polyurethane (PU)}

\textbf{Monomers:}
\begin{itemize}
\item Diisocyanate: \chemfig{O=[:30]C=[:330]N-[:30]R-[:330]N=[:270]C=[:210]O}
\item Polyol (diol or polyol): \chemfig{HO-[:0]R'-[:0]OH}
\end{itemize}

\textbf{Chemical formula:} \ce{(-O-R1-O-CO-NH-R2-NH-CO-)n}

\textbf{Reaction type:} Condensation polymerization (addition of isocyanate and hydroxyl groups)

\textbf{Polymerization reaction:}

\ce{n OCN-R2-NCO + n HO-R1-OH -> (-O-R1-O-CO-NH-R2-NH-CO-)n}

\textbf{Properties:}
\begin{itemize}
\item Highly versatile (can be rigid or flexible)
\item Excellent abrasion resistance
\item Good chemical resistance
\item Can be foamed to various densities
\item Good insulating properties
\end{itemize}

\textbf{Usage:} Flexible foams (cushions, mattresses), rigid foams (insulation), coatings, adhesives, elastomers (shoe soles), automotive parts

\vspace{0.5cm}

\textbf{Bakelite (Phenol-formaldehyde resin)}

\textbf{Monomers:}
\begin{itemize}
\item Phenol: \chemfig{*6(=-=-=-)=[:210]OH}
\item Formaldehyde: \chemfig{H-[:0]C(=[:90]O)-[:0]H}
\end{itemize}

\textbf{Chemical formula:} Complex cross-linked structure \ce{(C6H6O * CH2O)n}

\textbf{Reaction type:} Condensation polymerization with cross-linking (thermosetting)

\textbf{Polymerization reaction:}

\ce{n C6H5OH + n CH2O ->[acid or base catalyst, heat] (phenol-formaldehyde network) + n H2O}

\textbf{Properties:}
\begin{itemize}
\item First fully synthetic plastic (invented 1907)
\item Thermosetting (cannot be remolded after curing)
\item Hard and rigid
\item Excellent electrical insulator
\item Heat-resistant
\item Chemical-resistant
\item Dark color (brown or black)
\end{itemize}

\textbf{Usage:} Electrical insulators, switches, handles, kitchenware (vintage), automotive parts, billiard balls, jewelry

\vspace{0.5cm}

\textbf{Melamine-formaldehyde resin (Melamine)}

\textbf{Monomers:}
\begin{itemize}
\item Melamine: \chemfig{*6(-N(-[:90]NH_2)=N-(-[:270]NH_2)=N-(-[:90]NH_2)=N=)}
\item Formaldehyde: \ce{CH2O}
\end{itemize}

\textbf{Reaction type:} Condensation polymerization with cross-linking (thermosetting)

\textbf{Polymerization reaction:}

\ce{C3H6N6 + n CH2O ->[catalyst, heat] (cross-linked network) + n H2O}

\textbf{Properties:}
\begin{itemize}
\item Thermosetting plastic
\item Very hard and scratch-resistant
\item Heat-resistant
\item Stain-resistant
\item Can be colored and decorated
\item Flame-retardant
\end{itemize}

\textbf{Usage:} Dinnerware, countertops, laminates (Formica), whiteboards, adhesives, flame retardants

\subsection{Natural polymers}

\vspace{0.5cm}

\textbf{Cellulose}

\textbf{Monomer:} $\beta$-D-Glucose: \ce{C6H12O6}

\textbf{Chemical formula:} \ce{(C6H10O5)n}

\textbf{Reaction type:} Natural condensation polymerization (dehydration synthesis in plants)

\textbf{Linkage:} $\beta$(1$\to$4) glycosidic bonds between glucose units

\textbf{Properties:}
\begin{itemize}
\item Linear polymer with extensive hydrogen bonding
\item Crystalline structure gives high tensile strength
\item Insoluble in water
\item Not digestible by humans (lack of cellulase enzyme)
\item Most abundant organic polymer on Earth
\item Biodegradable
\end{itemize}

\textbf{Usage:} Paper production, textiles (cotton, linen), construction (wood), cellulose derivatives (rayon, cellophane, nitrocellulose)

\vspace{0.5cm}

\textbf{Starch}

\textbf{Monomer:} $\alpha$-D-Glucose: \ce{C6H12O6}

\textbf{Chemical formula:} \ce{(C6H10O5)n}

\textbf{Reaction type:} Natural condensation polymerization (biosynthesis in plants)

\textbf{Structure:} Mixture of amylose (linear, $\alpha$(1$\to$4) links) and amylopectin (branched, $\alpha$(1$\to$4) and $\alpha$(1$\to$6) links)

\textbf{Properties:}
\begin{itemize}
\item Energy storage polysaccharide in plants
\item Digestible by humans (amylase enzymes)
\item Forms helical structures
\item Swells in water, forms paste when heated
\item Biodegradable
\end{itemize}

\textbf{Usage:} Food (major carbohydrate source), thickening agent, adhesive, biodegradable plastics, textile sizing

\vspace{0.5cm}

\textbf{Proteins}

\textbf{Monomers:} Amino acids (20 common types): \chemfig{H_2N-[:0]C(-[:90]H)(-[:270]R)-[:0]COOH}

where R represents different side chains (e.g., H for glycine, CH$_3$ for alanine, etc.)

\textbf{Chemical formula:} Varies, general form $(C_xH_yN_zO_wS_v)_n$

\textbf{Reaction type:} Condensation polymerization (peptide bond formation)

\textbf{Polymerization reaction:}

\ce{n H2N-CHR-COOH -> (-NH-CHR-CO-)n + (n-1) H2O}

\textbf{Linkage:} Peptide bonds (amide bonds) between amino acids

\textbf{Structure:} \chemfig{-[:30]N(-[:90]H)-[:330]C(-[:30]H)(-[:270]R_1)-[:330]C(=[:270]O)-[:30]N(-[:90]H)-[:330]C(-[:30]H)(-[:270]R_2)-[:330]C(=[:270]O)-[:30]}

\textbf{Properties:}
\begin{itemize}
\item Four levels of structure: primary (sequence), secondary ($\alpha$-helix, $\beta$-sheet), tertiary (3D folding), quaternary (multiple chains)
\item Amphoteric (can act as acid or base)
\item Denatured by heat, pH changes, or chemicals
\item Biodegradable
\end{itemize}

\textbf{Usage:} Structural proteins (collagen, keratin), enzymes (biological catalysts), hormones (insulin), transport proteins (hemoglobin), food (meat, dairy, legumes)

\vspace{0.5cm}

\textbf{Natural Rubber (Polyisoprene)}

\textbf{Monomer:} Isoprene (2-methylbuta-1,3-diene): \chemfig{CH_2=[:30]C(-[:90]CH_3)-[:330]CH=[:270]CH_2}

\textbf{Chemical formula:} \ce{(C5H8)n} in cis configuration

\textbf{Reaction type:} Natural addition polymerization (biosynthesis in rubber trees)

\textbf{Structure:} \chemfig{-[:30]CH_2-[:330]C(-[:270]CH_3)=[:30]CH-[:330]CH_2-[:270]}

\textbf{Properties:}
\begin{itemize}
\item Elastic and flexible
\item Cis configuration gives coiled structure
\item Can be vulcanized (cross-linked with sulfur) for increased strength
\item Good electrical insulator
\item Waterproof
\item Biodegradable (though slowly)
\end{itemize}

\textbf{Vulcanization:} Cross-linking with sulfur to improve properties

\ce{Rubber + S ->[heat] Cross-linked rubber (stronger, less sticky)}

\textbf{Usage:} Tires, gloves, hoses, seals, footwear, elastic bands, medical devices

\textbf{Source:} Latex from rubber trees (Hevea brasiliensis)

\vspace{0.5cm}

\textbf{DNA (Deoxyribonucleic acid)}

\textbf{Monomers:} Nucleotides (phosphate + deoxyribose sugar + nitrogenous base)

\textbf{Bases:} Adenine (A), Guanine (G), Cytosine (C), Thymine (T)

\textbf{Reaction type:} Natural condensation polymerization (phosphodiester bond formation)

\textbf{Linkage:} Phosphodiester bonds between 3' and 5' carbons of sugar

\textbf{Properties:}
\begin{itemize}
\item Double helix structure (two antiparallel strands)
\item Base pairing: A-T (2 hydrogen bonds), G-C (3 hydrogen bonds)
\item Stores genetic information
\item Can be replicated
\item Relatively stable polymer
\end{itemize}

\textbf{Usage:} Genetic information storage, heredity, biotechnology (genetic engineering, forensics, medicine)

\subsection{Synthetic rubber and elastomers}

\vspace{0.5cm}

\textbf{Styrene-butadiene rubber (SBR)}

\textbf{Monomers:}
\begin{itemize}
\item Styrene: \chemfig{CH_2=[:30]CH-[:330]*6(=-=-=-)}
\item Butadiene: \chemfig{CH_2=[:30]CH-[:330]CH=[:270]CH_2}
\end{itemize}

\textbf{Chemical formula:} Copolymer with typical ratio 1:3 (styrene:butadiene)

\textbf{Reaction type:} Addition copolymerization (emulsion polymerization)

\textbf{Properties:}
\begin{itemize}
\item Good abrasion resistance
\item Good aging stability
\item Better than natural rubber for some applications
\item Less elastic than natural rubber
\end{itemize}

\textbf{Usage:} Automobile tires (most common use), shoe soles, adhesives, carpet backing

\vspace{0.5cm}

\textbf{Neoprene (Polychloroprene)}

\textbf{Monomer:} Chloroprene (2-chlorobuta-1,3-diene): \chemfig{CH_2=[:30]C(-[:90]Cl)-[:330]CH=[:270]CH_2}

\textbf{Chemical formula:} \ce{(C4H5Cl)n}

\textbf{Reaction type:} Addition polymerization (free radical polymerization)

\textbf{Properties:}
\begin{itemize}
\item Resistant to oil, heat, and weathering
\item Flame-resistant
\item More durable than natural rubber
\item Good chemical resistance
\end{itemize}

\textbf{Usage:} Wetsuits, laptop sleeves, electrical insulation, automotive belts and hoses, gaskets

\subsection{Biodegradable and bioplastics}

\vspace{0.5cm}

\textbf{Polylactic acid (PLA)}

\textbf{Monomer:} Lactic acid (or lactide, the cyclic dimer): \chemfig{CH_3-[:30]C(-[:90]H)(-[:270]OH)-[:330]COOH}

\textbf{Chemical formula:} \ce{(C3H4O2)n} or \ce{(-O-CH(CH3)-CO-)n}

\textbf{Reaction type:} Condensation polymerization (ring-opening polymerization of lactide)

\textbf{Polymerization reaction:}

\ce{n CH3CH(OH)COOH -> (-O-CH(CH3)-CO-)n + n H2O}

\textbf{Properties:}
\begin{itemize}
\item Biodegradable and compostable
\item Derived from renewable resources (corn starch, sugarcane)
\item Transparent and glossy
\item Low melting point (150-160°C)
\item Similar properties to PET
\item Recyclable
\end{itemize}

\textbf{Usage:} Biodegradable packaging, disposable tableware, 3D printing filament, medical implants (sutures, screws), bottles

\vspace{0.5cm}

\textbf{Polyhydroxyalkanoates (PHA)}

\textbf{Monomer:} Various hydroxyalkanoic acids, most common: 3-hydroxybutyric acid

\textbf{Structure (PHB):} \chemfig{CH_3-[:30]C(-[:90]H)(-[:270]OH)-[:330]CH_2-[:270]COOH}

\textbf{Chemical formula:} \ce{(-O-CH(CH3)-CH2-CO-)n} for PHB

\textbf{Reaction type:} Natural biosynthesis by bacteria (condensation polymerization)

\textbf{Properties:}
\begin{itemize}
\item Fully biodegradable (even in marine environments)
\item Produced by bacterial fermentation
\item Thermoplastic
\item Biocompatible
\item Similar properties to polypropylene
\end{itemize}

\textbf{Usage:} Biodegradable packaging, agricultural films, medical applications (sutures, tissue engineering), food containers