bme312 natural polyesters

plastics pollution

plastic pollution can alter habitats and natural processes, reducing ecosystems’ ability to adapt to climate change, directly affecting millions of people’s livelihoods, food production capabilities, and social well-being

plastics impact

the toxic chemical additives and pollutants found in plastics threaten human health on a global scale. scientifically-proven health effects include causing cancer or changing hormone activity (endocrine disruption), which can lead to reproductive, growth, and cognitive impairment

thermoplastics

make up about 75% of worldwide plastic production, a trillion plastic bags are consumed worldwide, less than 1% are recycled, MW range is 20,000 to 500,000 daltons, most polymers have C and Hs and are composed of repeated units

examples of most widely used thermoplastics

polyethylene (including HDPE, LLDPE, LDPE), polypropylene, polyvinyl chloride, and polyethylene terephtalate (PET)

thermoplastic removal

PVC being incinerated can cause harmful emissions, during its incineration up to 2mg per gram of phosgene is generated which is one of the most dangerous gases, it’s an asphyxiant gas used as a weapon during ww1

how do we reduce plastic waste

recycling efforts (technology & organizations), reduction in use (reusable products like glass, SS), developing new materials that can degrade

polyester definition

a polymer that contains the ester functional group in the repeat unit of their main chain

what is PHA and how is it made

polyhydroxyalkanoates are polyesters produced by direct fermentation, no multistage technology is needed. constitute a family of polymers of various chemical structures, consisting of monomers containing between 3-12 or more carbon units

how can PHAs be synthesized

from feedstocks such as saccharides, organic acids, alcohols, mixtures of CO2 and H2, products of plant biomass hydrolysis, industrial wastes of sugar and palm oil production, hydrogen-containing products of processing of brown coals and hydrolysis of lignin

PHA chemical structure

can be divided into 3 groups depending on the number of carbon atoms in the monomer units: (1) short chain length (SCL) PHAs, 3-5 carbon atoms. (2) medium chain length (MCL) PHAs, 6-14 carbon atoms. (3) long chain length (LCL) PHAs, which consist of 17 and 18 carbon atoms

SCL PHAs

consist of poly-R-hydroxyalkanoates containing 3-5 carbon units, synthesized by different bacteria

MCL PHAs

synthesized when the PHA producing strain is cultivated on the medium containing n-alkanoates or their precursors. some bacteria produce these PHAs.

PHA synthesis

cheese and sour milk production wastes, materials from sugar industry, and wastes from palm oil production can be used as substrates for PHA synthesis. when different fat-containing industrial wastes such as spent cooking oils and fats, which can be found in great quantities, residues of animal fats that can be processed into triacylglycerides, and meat and bone waste hydrolysates can be used as substrates for PHA synthesis

crystallinity in PHA synthesis

the degree of crystallinity of PHAs with different structure can vary widely, between 10-20 and 70-80%, and this parameter can be controlled and dependent on:

-changing the chemical composition of the polymers produced under different conditions of cultivation of PHA-producing bacterial strains

-different carbon nutrition conditions

general properties of PHAs

biodegradable, biocompatible, low permeability to water, UV resistant, optical activity, antioxidant properties, piezoelectricity-electric charge that accumulates in certain solid materials in response to applied mechanical stress, 60-80% crystallinity, stiff material of high tensile strength, variation in monomer fractions of a PHA leads to considerable changes in its thermo-mech and fibrous properties

PHA surface properties

hydrophilic/hydrophobic balance of the surface is a major parameter that indirectly characterizes biological compatibility and influences cell adhesion and viability. this balance is expressed as water contact angle. surface energy and surface roughness is another major parameter that can influence the behavior of cells

altering properties of PHA

properties can be controlled by varying the composition of the culture medium and tailoring the chemical structure of the polymer (MW distribution depends on bacterial fermentation conditions), can be processed from various phase states (powder, solution, gel, melt) using conventional techniques, you can also change the content

applications of PHA

glues, fillers, personal hygiene materials, food, SCL PHAs used to fabricate packaging films/shopping bags/containers/paper coatings

biomed applications of PHA

cardiac patch and heart valve, stent, drug delivery, wound dressing, nerve guidance conduit, blood vessel, sutures, bone and cartilage scaffold

PHA limitations

processing PHAs is very tricky, study showed perhaps process it in two steps (melt the material and then twin screw extrusion)

overall description of PHB

natural polymers are made from renewable biomass, discovered PHB in 1925, found to be a part of PHA family, similar properties to polypropylene. stands for polyhydroxybutyrate

three classes of PHB

based on MW:

1. low MW: accumulated by eukaryotes and archaebacteria, also known as complexed PHB or cPHB. MW<12,000Da

2. high MW: 200,000-30,000,000 Da depending on growth conditions

3. ultra high MW: synthesized by recombinant E. Coli, MW>30,000,000 Da, used for blending or composite material

PHB carbon chain classification

SCL: comprised of monomers with 3-5 carbon atoms per repeat unit, MCL: comprised of monomers with 6-14 carbon atoms in the repeat unit. the conversion from scl to mcl results in change in physical properties from crystalline to low crystalline elastomeric thermoplastics

general properties of PHB

transparent films are produced at a melting point higher than 130 degrees C and is biodegradable without residue, crystalline, brittle, biodecomposable, non-toxic, insoluble in water, piezoelectric

synthesis of PHB

can be produced by sugars and plant oils (wastes), feeding medium with carbon promotes PHB accumulation, production is directly proportional to the carbon:nitrogen ratio, bacteria use various c4 and c5 sources to produce polymer

impact of carbon in fermentation process of PHB

the carbon used in the fermentation process accounts for 50% of the cost. 3 enzymes involved in the biosynthesis of PHB

isolation and purification of PHB

solvent extraction (PHB is soluble in organic solvents, very expensive step), enzymatic extraction (use lysozymes and DNA to solubilize the peptidoglycans and the nuclear acids)

applications of PHB

packaging (blow molded bottles, disposable items), medical (pericardial patches, vascular grafts, heart valves, controlled drug release, tissue scaffolds)

limitations of PHB

a major problem for extensive production/commercialization of PHB is their high production cost as compared with plastics derived from petrochemicals

what has been done to try and reduce production cost of PHB

developing efficient bacterial strains and optimizing fermentation and recovery processes

limitations having to do with PHB properties

semi crystalline thermoplastic produced from microorganisms by fermentation of renewable carbohydrate feedstocks, relatively high melting point of about 160 to 180 degrees celsius and is difficult to process due to its narrow processing window

how to improve PHB processability and mech properties

blend it with plasticizers and other polymers like PLA, PVA, binders