Lecture 11: Natural polymers Flashcards
what are examples of natural polymers?
cellulose lignin starch chitin chitosan protein
describe the structure of cellulose
repeating beta 1,4 glucan unit
cellulose is difficult to process in what?
solution or as a melt
what are solvents used with cellulose?
NMMO
DMAc
ionic liquid
NaOH/urea
describe the structure of natural polymers
repeating alpha-1,4-glucan and alpha-1,6-glucan units
amylose is ____ and amylopectin is ____
a) linear
b) amylopectin
amylose is linear
amylopectin is branched
what are some characteristics of natural polymers?
gelatinization
poor wet mechanical properties
describe the structure of chitin
N-acetylglucosamine units connected by beta-1,4-linkages
what is the main component of exoskeletons of arthropods?
chitin
how is chitosan formed?
deacetylation of chitin using sodiun hydroxide
what are some properties of chitin?
antibacterial
anti-inflammatory
how is protein formed as a natural polymer?
condensation polymerization of AAs
what is a bioplastic?
biopolymer that can be shaped or molded via plastication or crosslinking
what is a problem for synthetic plastics?
disposal problems
- limited recycling option
- limited landfill space
- incineration may release toxins
- higher dependence on fossil fuels
what is PLA? what is it from?
polylactic acid
type of bioplastic
derived from corn
what is PHA? what is it from?
polyhydroxyalkanoates
type of bioplastic
harvested from bacteria
what is cereplast?
starch based bioplastic
what are proteins used for protein based bioplastics?
soy
casein
corn zein
what is soyOyl?
veg oil based bioplastic
what are advantages of biopolymers?
- renewable feedstock
- domestically grown
- CO2 neutral
- compostable
- biocompatible /bioabsorbable
- energy saving w/ lower processing temp
what are disadvantages of biopolymers?
- more expensive
- low end mechanical properties
- low service temp
- not as durable in harsh environments
what kind of proteins are used for protein bioplastics?
vegetal (corn zein, wheat gluten, soy, sunflower)
or animal (Caseins, whey, gelatin, myofibrillar)
in protein bioplastics, what happens to the proteins during processing?
what are they formed into?
proteins go into solvent or thermoplastic process\
formed into coatings, films, molded materials
describe wheat gluten
co-product of starch industry
what are advantages of what gluten based materials?
- good film forming properties
- high availability at low price
- biodegradability and non-ecotoxicity
- unique functional properties (adhesive, high gas barrier/perm-selectivity)
what are unique functional properties of gluten-based materials
adhesive
high gas barrier
high gas perm-selectivity
what are drawbacks of wheat gluten based materials?
poor water resistance
poor mechanical properties
describe the tensile strength and strain of
a) wheat gluten based materials
b) biodegradable polyesters
c) conventional polymers
wheat gluten materials has lowest tensile strength and breaks at lower strain
biodegradable materials break at higher strains
conventional polymers have intermediate tensile strength and resistance to strain
how are barley protein films made?
barley protein is the byproduct of starch or beta-glucan processing
barley protein + glycerol undergoes hot pressing to produce films
in protein based bioplastics, what are properties that can be modulated?
- crosslinking
- lamination
- composites
what is the equation for gas selectivity?
s = P (co2) / P(o2)
how are SPI/cellulose nanocrystal composites produced?
- cotton linter pulp + sulfuric acid
- cellulose nanocrystals + SPI + glycerol
- hot pressing
describe the crystallinity of natural polymers
natural polymers have:
- crystalline regions
- amorphous regions
- void regions
- interfibrillar tie molecules between microfibrils to form a fiber
what properties do natural polymer nanocrystals have?
- reinforcing mechanical properties
- improving barrier properties
- stabilizing food emulsions
- swelling properties
- thermal stability
how does oat protein gel in a cold gelation process?
- oat protein + OPI solution at pH8
- add GDL (glucono-delta-lactone)
- cool
what are functions of oat protein gelation?
protects enzymes and probiotics in harsh stomach conditions
controls release of bioactive compounds
what are surface multilayer structures of electrospun micro/nano fibers?
- branched
- porous
- necklace-like
- non-cylinder
what are inner multilevel structures of electrospun fibers?
- peapod
- wire in tube
- multiwalled
- multichannel
what are uses of electrospun fibers?
- gas sensors for food safety
- smart food preservation
