forensics plastics

Polyethylene Terephthalate (PETE)

RC of 1

Polyethylene Terephthalate (PETE)

~1.37 g/cm^3

Polyethylene Terephthalate (PETE)

Soft drink/beverage bottles, carpet, fiberfill, rope, scouring pads, fabric, Mylar

Polyethylene Terephthalate (PETE)

Shrivels with heat, burns slowly with yellow flame and light smoke

Polyethylene Terephthalate (PETE)

Polymerizes by condensation

Polyethylene Terephthalate (PETE)

High-Density Polyethylene (HDPE)

RC of 2

High-Density Polyethylene (HDPE)

~0.95 g/cm^3

High-Density Polyethylene (HDPE)

Food containers, bags, lumber, furniture, flower pots, signs, trash cans, toys

High-Density Polyethylene (HDPE)

Burns slowly with a yellow flame, smells like candle wax

High-Density Polyethylene (HDPE)

Polymerizes by addition, monomer units more linear than other type

High-Density Polyethylene (HDPE)

Polyvinyl Chloride (PVC)

RC of 3

Polyvinyl Chloride (PVC)

~1.38 g/cm^3

Polyvinyl Chloride (PVC)

Food packaging, shampoo containers, construction (pipes), tiles, credit cards

Polyvinyl Chloride (PVC)

Burns with a green flame, acrid smell

Polyvinyl Chloride (PVC)

Polymerizes by addition (1)

Polyvinyl Chloride (PVC)

Low-Density Polyethylene (LDPE)

RC of 4

Low-Density Polyethylene (LDPE)

~0.92 g/cm^3

Low-Density Polyethylene (LDPE)

Food containers (specifically bags), grocery bags, plastic wrap, etc.

Low-Density Polyethylene (LDPE)

Burns slowly with a blue flame with yellow tip, smells like candle wax

Low-Density Polyethylene (LDPE)

Polymerizes by addition, ethylene monomer units branch out more than other type

Low-Density Polyethylene (LDPE)

Polypropylene (PP)

RC of 5

Polypropylene (PP)

~0.90 g/cm^3

Polypropylene (PP)

Food containers, medicine containers, automobile batteries, carpet, rope, plastic wrap, lab equipment

Polypropylene (PP)

Burns slowly with a blue flame with yellow tip, has a sweet smell

Polypropylene (PP)

Polymerizes by addition (2)

Polypropylene (PP)

Polystyrene (PS)

RC of 6

Polystyrene (PS)

~1.05 g/cm^3

Polystyrene (PS)

Styrofoam, tableware, coffee cups, toys, lighting, signs, insulation

Polystyrene (PS)

Burns quickly with a yellow flame, releases a dense black sooty smoke

Polystyrene (PS)

Polymerizes by addition, reacts with acetone (1)

Polystyrene (PS)

Polycarbonate (PC)

RC of 7 (1)

Polycarbonate (PC)

~1.20 g/cm^3

Polycarbonate (PC)

Shatterproof glass, eyeglass lenses

Polycarbonate (PC)

Orange flame with black sooty smoke, has a faint sweet odor

Polycarbonate (PC)

Polymerizes by condensation, clear

Polycarbonate (PC)

Polymethyl Methacrylate (PMMA)

RC of 7 (2)

Polymethyl Methacrylate (PMMA)

~1.16 g/cm^3

Polymethyl Methacrylate (PMMA)

Plexiglas, glass substitute

Polymethyl Methacrylate (PMMA)

Light blue flame with white tip, drips, floral/fruity smell

Polymethyl Methacrylate (PMMA)

Polymerizes by addition, reacts with acetone (2)

Polymethyl Methacrylate (PMMA)

HDPE vs LDPE

Condensation

the addition of two monomer units produces a small by-product like water or methane

Addition

no by-product is lost

Thermoset

Undergo a process known as curing, where a plastic is irreversibly hardened from a softer resin form.

This can be induced by heat, UV radiation, or mixing with a catalyst (like two-part resins).

Hard to melt and reuse plastic

Since these plastics cannot be melted, they also cannot be recycled commercially.

Thermoplastic

Are not cured.

These plastics will become moldable/malleable when heated beyond a certain point

Useful in injection molding or extrusion.

Suitable for commercial recycling.

Water

~1 g/cm^3

NaCl Solution (10%, 25%, saturated)

~1.07 g/cm^3, ~1.19 g/cm^3, ~1.20 g/cm^3

Vegetable oil

~.91-.93 g/cm^3

Isopropyl Alcohol 25%, 50%, 100%

~.85 g/cm³, ~.88 g/cm³, ~.786 g/cm³

Float on water

HDPE

LDPE

PP

Floats on vegetable oil

HDPE (partial)

LDPE

PP

Floats on NaCl (10%)

HDPE

LDPE

PP

Floats on NaCl (25%)

HDPE

LDPE

PP

PS

Floats on NaCl (saturated)

HDPE

LDPE
PP
PS

PMMA (partial)

Floats on IPA (25%)

LDPE
PP

Floats on IPA (50%)

HDPE (partial)

LDPE

PP

Floats on IPA (100%)

None float

Polymerization

the process of reacting monomer molecules together to create a polymer

Degree of Polymerization

Amount of monomer units in a polymer