Review for Exam #1

Outline

• Product deterioration• Paper and paperboard• Glass• Metal• Plastics• Retortable pouch

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Product Deterioration

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Mechanisms of Product Deterioration

• Biological

• Enzymatic

• Physical

• Chemical

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Biological Mechanisms

• Microorganisms: Bacteria, molds, yeasts– Acid/alcohol/gas/pigment/toxin produced– Can be pre-harvest or post-harvest decay

• Macroorganisms: Insects, parasites, rodents– Damage 5-10% of US grain crop– Insects cause only minor damage, but allows for

microbial invasion– Rodents consume large quantity of food and contaminate

with filth

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Enzymatic Mechanisms• Enzymes: Large protein molecules that act as biological

catalysts; activity is substrate specific and depends on temperature and pH

• Living tissue maintains enzyme balance– Harvest/slaughter disrupts pH & enzyme balance– Enzyme activity becomes uncontrolled– Can lead to tissue damage and spoilage

• Ascorbic acid oxidase, lipase, lipoxygenase, PPO, pectic enzymes, peroxidase, protease, thiaminase, PG

• Enzymatic browning: Reaction of O2 with O-dihydroxyphenol in presence of PPO to produce quinone

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Physical Mechanisms• Forces

– Bruising, crushing, wilting

• Light− Chlorophyll, anthocyanins, carotenoids, Vit. (B2, C) can be destroyed− Discoloration of fresh meat

• Temperature− Rates of reactions generally double for every 10 °C temperature rise− Protein denaturation, emulsion breakdown, dehydration could take

place; this can result in textural changes− Cold: Discoloration/texture change with freezing; chill injury for fruits

• Oxygen• Oxidation destroys Vit. A&C, alters color; off-flavors; mold growth

• Moisture• Lumping, caking, condensation, crystallization, stickiness

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Chemical Mechanisms• Auto-oxidation

− Unsaturated fatty acids are susceptible to autocatalytic breakdown in presence of oxygen Proceeds by free-radical chain reaction Products formed can cause rancidity, color change, Vit. (A, C, E) destruction

• Maillard browning• Lipid hydrolysis/oxidation• Protein denaturation/hydrolysis• Oligo/polysaccharide hydrolysis/oxidation• Polysaccharide synthesis• Degradation of natural pigments• Glycolytic changes

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Paper and Paperboard

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Composition of Wood Pulp• Cellulose (~50%)

– Long chain, high molecular weight polymer of glucose– Moderately resistant to chlorine and dilute NaOH– Relatively resistant to oxidation with bleaching agents

• Hemicellulose (~20%)– Shorter chain, lower molecular weight polymers of xylose, mannose,

arabinose, galactose, and uronic acid– Soluble in dilute alkali– Its quantity and not chemical nature determines properties– Responsible for hydration & bonding during beating of pulp

• Lignin (~30%)– Highly branched alkylaromatic thermoplastic polymer of substituted

phenyl-propane units– Has no fiber-forming properties– Attacked by Cl & NaOH & forms soluble, dark brown derivatives– Softens at ~160 °C 10

Softwood and Hardwood

• Softwoods– Coniferous trees: Strong and rough paper– Fibers: ~ 1/4” length– Fiberboard, corrugated

• Hardwoods– Deciduous trees: Weak and fine paper– Fibers: ~ 1/10” length– Printing of labels

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Papermaking Operations

• Pulping• Forming paper• Pressing and drying• Converting

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Goals of Pulping

• Remove all lignin (intercellular substance) to free the fibers– The more the lignin is retained, the less strong the paper

and faster it loses color and strength• Keep some of the hemicellulose• Keep all of the cellulose• Separate the fibers without damaging them so that

they can be formed into a sheet

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Pulping for Different Starting Materials

• Hardwood/softwood (mechanical): Debark, grind, wash & refine, bleach and/or color

• Hardwood/softwood (chemical): Debark, chip, digest, wash & refine, bleach and/or color

• Other plant material: Digest, wash & refine, bleach and/or color

• Waste paper: Wash & refine, bleach and/or color

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Types of Pulp

• Mechanical

• Chemical

• Semi-chemical

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Mechanical Pulp

• Force wood against rapidly revolving grindstone Groundwood pulp

• Groundwood pulp contains 70-80% fiber bundles, broken fibers, and fines in addition to individual fibers

• Higher yield than chemical pulp since lignin is also utilized• Used for newsprint and magazine papers because of low

cost and quick ink-absorbance (because of broken fibers)• Used for folding cartons, wall papers, tissues• High bulk, excellent opacity, low strength

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Chemical Pulp• Use high temperature and alkali to dissolve lignin• High quality pulp, but only ~50% yield• Generally, bark is removed for chemical pulping• Alkaline processes

– Soda process• First chemical pulp process (1851)• Boil wood in 4-6% by weight of NaOH @ 170 °C; not popular now

– Sulfate/Kraft process• Operator accidentally emptied vat before full cook• Resulted in stronger paper; most popular method now• Uses NaOH & Na2S; Na2SO4 is used as make-up chemical in recovery process

• Sulfite processes– Acid sulfite process

• Acidic liquor → Ca. Bisulfite and excess of SO2 is used• Light colored pulp; easily bleached; not popular method, now

– Bisulfite process• Uses liquor of Mg or Ammonium Bisulfite & SO2; cook at pH of 4.0 17

Semi-Chemical Pulp

• Softening of wood chips with sulfurous acid or bisulfite followed by rubbing or grinding to produce pulp

• This is milder than the chemical process and hence hemicelluloses are retained to a greater extent, resulting in higher strength and yield

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Comparison of Pulping Processes

Mechanical Semi-chemical Chemical

Yield 90-95% 50-90% 40-55%

Fibers Short, impure Intermediate Long, pure, strong, stable

Print Good print quality

Intermediate Poor print quality

Bleaching Difficult Intermediate Easy

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Paper Manufacturing Process(Fourdrinier Machine)

• Named after its financiers (British)• Continuous, horizontal, moving belt of fine wire

mesh• Deposit dilute suspension of fibers on screen• 95% of water drained through wire• Fibers interlay randomly• Square grain (fiber alignment and hence strength in

machine direction -- MD and cross direction -- CD are ~ same)

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Fourdrinier Machine

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Paper Manufacturing Process(Cylinder Machine)

• Cylinder covered with wire cloth rotated (partially submerged in suspension)

• Vacuum applied inside and so water drains inside and paper web forms outside

• Web is picked up by felt which is pressed by a roll• Series of vats provide individual plies of fiber which

are matted together• Much stronger in MD than CD

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Cylinder Machine

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Properties of Paper(Basis Weight)

• Mass in grams per square meter (gsm)– Paper: ≤ 250 gsm– Paperboard > 250 gsm– Newsprint: 49– Grocery bags: 49-98– Kraft liner board: 127-439– Folding box board: 195-586

• Also expressed as lbs per 1000 sq. ft. kg per 205 m2

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Properties of paper(Caliper or thickness)

• Thickness of single sheet measured under specific conditions– Newsprint: 85 m– Linerboard: 230-640 m

• It is also expressed as mils– 1 mil = 1 point = 0.001 inch– Paperboard: > 12 pts– Corrugating medium: 9 pts– Folding cartons: 15-30 pts

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Paperboard• Paperboard or board is defined by TAPPI as paper products with

basis weight > 250 gsm• Chipboard

– Made from recycled fibers on a cylinder machine

• Manila board– Made from virgin pulp and recycled fibers on cylinder machines

• Kraft Cylinder board– Made from virgin Kraft pulp and recycled Kraft fibers

• Kraft Fourdrinier board (Solid Bleached Sulfate Board)– Also called White Board or Food Board– May be clay coated to give better printing surface– May be waxed or polyethylene coated to give moisture resistance– May be coated with PET for baking foods or reheating frozen foods

Note: It is unlawful to have direct contact between food and recycled paper fibers26

Cardboard Box• Liner

– Usually unbleached kraft– Sulfate pulping of softwood on Fourdrinier machine– 16 pts– Basis wt = 42 lbs/1000 ft2

• Medium– Usually unbleached kraft– Semi-chemical hardwood on Fourdrinier machine– 9 pts– Basis wt = 26 lbs/1000 ft2

• Glue– Corn starch– Good bond, but insects like it 27

Manufacture of Corrugated Board

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FlutesType Height (cm) # of flutes per m

A 0.47 110B 0.246 154C 0.361 138E 0.114 315

• Flutes: Act like arches in resisting flat crush; act like columns and resist edge crush; trap air and give some insulation properties

• A → Max. cushioning and good top to bottom compression• B → High resistance to flat crush• C → Compromise of properties; widely used• E → Like solid paperboard (cushions & insulates @ low weight)

Solid paperboard: Several layers of 0.13-0.33 mm paper to yield 0.8-2.8 mm (557-158 gsm) 29

Testing of Paper Products• Linerboard

– Bursting strength (Mullen tester)– Basis weight– Puncture resistance– Stiffness– Tear resistance– Tensile strength– Moisture content– Water resistance– Caliper

• Medium– Ring crush or stiffness test

• Corrugated board– Bursting strength, Edge compression, Flat crush, Pin adhesion

• Finished corrugated box– Puncture test, Compression, Drop test, Impact test

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Advantages and Disadvantages of Paper• Advantages

– Paper can provide a barrier to light– Paper can be made into a variety of single wall bags (eg. grocery

bags) and multi-wall bags (eg. flour, sugar)– Paperboard provides strength & protection in many packages– Paper and paperboard can be coated or laminated with wax,

polyethylene or polyvinylchloride to improve moisture and gas barrier properties and allow sealability

– Only uncoated/unlaminated paper and paperboard can be recycled

• Disadvantages– Negligible moisture, gas or microorganism barrier properties when

not coated or laminated– Not heat sealable unless coated or laminated– Coated/laminated paper/paperboard are, in general, not recyclable

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Glass

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Types of Glass Containers• Bottles

– Beer, ketchup, salad dressing, vegetable oil, beverages, vinegar, wine

• Jars– Wide mouth containers for fruits, vegetables, jams,

preserves, instant coffee, coffee whiteners, baby foods• Jugs

– 1 gallon bottles with small neck, often with a carrying handle -- institutional, industrial, and household products

• Carboys– 3-13 gallon capacity -- enclosed in a wooden overpack;

for drinking water, distilled water, and industrial use33

Blow and Blow Bottle Making Process

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Press and Blow Bottle Making Process

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Types of Glass• Soda-lime glass

– Least expensive, chemically durable, most popular– Soda, Na2O, potash, K2O dec. visc. below that of silica & helps use

low melt temp. & improves “fining” (clearing up) qualities of glass

• Borosilicate glass– Use of B2O3 yields low thermal expansion coeff. (good thermal

shock resistance) and high chemical resistance– B2O3 does not dec. visc. as much as soda; thus, high temp, cost– Pyrex glass is a brand name for a type of borosilicate glass

• Lead silicate glass– Contains mainly PbO and SiO2

– PbO replaces lime (CaO) in the soda-lime process– Lead inc. brilliance, expands working range (useful to make art

objects & intricate shapes w/o freq. reheating), but dec. hardness36

Closures for Glass Containers• Designed for internal pressure (200 - 800 kPa)

– Crown cap or twist-off cap -- steel– Roll-on or spin-on aluminum closure

• Designed for vacuum seal– Lug-type– Twist cap– Press-on twist-off cap– Pry-off

• Designed only to contain materials in package– Screw top with minimum thread engagement

Metal closures: Screw caps, crowns, lug caps, spin-on or roll-on37

Advantages of Glass• Moderate cost• Easily shaped and formed at high speeds• Chemically durable• Strong; survives all processing conditions• Easily dispenses product• Resealable• Microwaveable, impermeable to gases & moisture• Tasteless, odorless, transparent• UV inhibitors can give protection from UV• Numerous closure applications• Recyclable 38

Disadvantages of Glass

• Breakable• Heavy• No anti-static agent to protect from dust• Color limitations• Secondary packaging limitations• Cylindrical shape occupies excessive shape in

storage

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Metal

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Metals Used in Food Packaging• Aluminum (with small amounts of Mg & Mn)

– For cans and foils• Tin & Steel

– Tinplate (for tin/steel cans)• Chromium & Steel

– Electrolytic chrome-coated steel (ECCS); also called Tin-free steel (TFS)

• Lead & Copper– Used for soldering (Pb) or welding (Cu) of 3-piece

tinplate and ECCS containers41

Tin Free Steel (TFS)

1. Chemically passivated steel, which has a phosphate-chromate film on the surface

2. Chrome-coated steel with a layer of chromium oxide on top of the metallic chromium

3. Aluminum coated steel

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Tinplate and ECCS

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Types of Cans• Three-piece

– Soldered side seam (not used in the U.S. because of lead)• Exception: Lead-free solder used for canned asparagus

– Welded side seam (only method in U.S.)

• Two-piece (developed in the late 1970s)– Drawn & Ironed (D&I)

• Flat metal sheet is formed into a cup by a punch in a circular die• Thickness of cup is uniform throughout• Ironing dies in ironing press reduce thickness and increase height• Wall is thinner than base

– Drawn & Redrawn (DRD)• Sequential drawing of cup into dies of smaller diameter• Redistributes base to wall• Wall & base thickness same as original sheet metal thickness

Advantages of two-piece method: Technical, economical, aesthetic44

Manufacture of Drawn and Ironed Can

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Manufacture of Drawn & Redrawn Can

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Manufacture of Three-Piece Cans

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Can Welding Process

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Can End/Lid

• The lid is double-seamed onto the body for both types of cans

• The expansion rings on the lid act as diaphragms– Expand during processing & return to original position

later (vacuum)

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Can End Embossing Pattern

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Profile of Can End

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Double Seaming Operation

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Main Components of a Double Seam

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Double Seam Terminology

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Aerosol Cans• Developed by Dept. of Agriculture based on need

for U.S. Army in 1942– To combat insects on Japanese islands during WW-II

• Thicker gauge steel can (or ECCS) than soup cans– To withstand pressure

• Interior is coated to withstand effects of propellant and product– Oleoresins, vinyl, acrylic, phenolic, and epoxy-phenolic

compounds• Filling of container is through valve stem or under

the dome55

Components inside Aerosol Containers

• Active ingredient (product)• Propellants (provide pressure to force product out)

– Volatile• Blend of propane, butane, and isobutene

– Non-volatile propellants• CO2, N2, NO, air

• Solvent (brings product in solution with propellant)

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Advantages of Metal

• Strong• Resistant to high heat and pressure• Good barrier to light, oxygen, and moisture• High speed can production (and product filling)

possible

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Disadvantages of Metal

• Heavy– Transportation cost is high

• Can be difficult to open• Cylindrical shape results in wastage of space during

storage and transportation• BPA concerns

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Plastics

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Monomers and Polymers• Monomer

– Ethylene (CH2 = CH2)– Propylene (CH3-CH=CH2)– Vinyl chloride (CH2=CHCl)

• Homopolymer– Polyethylene (PE), Polypropylene (PP), Polyvinylchloride (PVC)

• Copolymer (Eg., EVOH, LLDPE)– Random (ABAAABBBBABBA)– Alternate (ABABAB)– Block (AAAAABBBBB)

• Graft ( A- - -A- - -AB B BB B B)

• Combination (Some combination of above) 60

Commonly Used Types of Plastics

1. Polyethyleneterephthalate (PET)2. High density polyethylene (HDPE)3. Polyvinylchloride (PVC)4. Low density polyethylene (LDPE)5. Polypropylene (PP)6. Polystyrene (PS)7. Other (Multilayer) – PC is included in this

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Crystalline and Amorphous Structures• Crystalline

– Long-range orderly structure• Ionically bonded: Solidification of salts from molten fluid or crystallization

from a solution• Covalently bonded: Diamond, silica, graphite

– Polymorphism: Ability to exist in more than one crystal form (for pure elements, polymorphism is called allotropy; diamond, graphite, and fullerenes are allotropes of Carbon)

• Ice: Hexagonal, cubic, rhombohedral

– Polyamorphism: If amorphous phases are also present

• Polycrystalline (most metals and many ceramics)– Composed of crystals of different sizes oriented in diff. directions

• Amorphous (or vitreous or glass-like)– No long-range orderly structure– Latent heat of fusion is not released during formation of glass 62

Films• Thickness less than 10 mils or 0.01”• Laminate

– Combining two or more films with an adhesive• Composite

– Combining two or more thin streams by co-extrusion• Shrink film (PVDC, PVC)

– Temperature range of shrinking, degree of shrinking, and shrink tension are the 3 important parameters

• Stretch film (PE, LDPE, PVC, EVA, PP)– Stretchability, stress, re-stretch force, and breaking

strength are the 4 important parameters63

Manufacture of Films

• Thermoplastic is extruded and converted into films by– Tubular (or blown) film

• Has an annular die ring that may be rotating to ensure uniform film thickness

• Air is blown into the tube to maintain the bubble• Guide rolls, pinch rolls, wrap-up reel are downstream

– Flat film (or sheet film or cast film or slit die film)• Plastic is extruded through slit die• Chilled rollers form the uniform thickness film

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Flat Film and Sheet Extrusion

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Tubular Film or Blown Film Extrusion

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Manufacture of Containers• Extrusion blow molding

– Single mold, handleware, large containers, co-extrusion possible; can not run PET, limited precision, trim scrap

• Injection molding• Injection blow molding• Injection stretch blow molding• Thermoforming

– Matched die (matched mold) forming– Vacuum forming– Pressure forming– Ring and plug (press) forming

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Extrusion Blow Molding

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Injection Molding

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Injection Blow Molding

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Injection Stretch Blow Molding

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ThermoformingMatched die (matched mold) forming

Vacuum forming

Pressure forming

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Advantages of Plastic• Lightweight• Durable (no rot or rust; only UV degrades it)• Easy sealability• Various shapes, handles, and spouts• Light control & package appearance (clear to hazy)• Easy to print and apply labels on• Good strength• Good tear resistance and puncture resistance

– Better than paper, cellophane, Al foil• Low temp. flexibility (cellophane embrittles @ 40 °F)

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Disadvantages of Plastic

• Migration/leaching• Environmental concerns (landfill vs. recycling)• Improving barrier properties increases cost

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Retortable Pouch

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Retortable Pouch (Overview)• It is a flexible package (also called stand-up pouch)• Product is hermetically sealed in it just like in a can

– Shelf life is comparable to that of a product in a can• Use began in the 1950s with the military for MREs• US Army Natick, Reynolds Metals Company, and

Continental Flexible Packaging jointly received the 1978 IFT Industrial Achievement Award for it

• Product can be eaten cold or warmed by immersing pouch in hot water

• Sometimes, the pouches are placed in a cardboard box for aesthetic reasons or for puncture resistance Companies: Capri Sun, Star-Kist, Bumble Bee 76

Layers of a Retort Pouch• Polypropylene (food contact surface)

– Good heat seal surface, flexible, strong• Aluminum foil

– Barrier to O2, moisture, light, odor– Stiffness permits tear-notch

• Nylon– Abrasion/puncture resistance

• Polyester– High temperature resistance, tough, printable surface

Note: The existence of 4 layers makes recycling difficult77

Types of Retort Pouches• Pre-formed

– 3 sides already sealed by pouch manufacturer• In-line formed

– Web-fed roll-stock, tensioning device (to smooth the surface), web folding assembly (fold web in half), heat sealer (seal vertical sides), roller knife (separate individual pouches)

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Advantages of Retortable Pouch

• Easy to open unlike cans– Notch facilitates easy opening

• Less transportation cost– Lighter than a can and can be flattened

• Less storage space for empty containers• Less over-cooking and hence better product quality

– For same volume as a can, smallest dimension of pouch is less than that for a can

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Disadvantages of Retortable Pouch• Capital cost for new equipment is high

– This is not a commonly used equipment and hence an investment has to be made to procure it

• Thermal process is more complex– Where is the cold spot? How much air is remaining and

where is the air bubble?• It is easily punctured

– Secondary packaging may thus be needed• Filling operation is slower than for cans• Leak detection equipment (burst tester, tensile

tester) is different80