physical polymer chemistry of pet isbt bottle and closure committee

Research, Development & Engineering

Physical Polymer Chemistry of PET

ISBT Bottle and Closure Committee

Eric MorrisonEcolab Food and Beverage R&D

October 18, 2005


ISBT Bottle and Closure Committee October 18, 2005

Bottle Failure – Cause and Effect (Ichikawa) Diagram

Bottle Failure Probability

Storage (Post-filling) Operational

Bottle Chemical

Temperature

Physical handling

Dust/Debris Carbonation level

Age

Mold/Manufacturer

Uniformity/Gate Protrusion

Bottle Strength (IV)

Alkalinity

Conveyor Lubricant

Oils, greases

Crystallinity

Warmer treatment

Cleaning Chemical

Fill-height

Storage (Pre-filling)

Temperature

Humidity

Duration

Humidity




Objective: Characterize physical changes occurring in beverage bottles during filling, processing, and storage

•Physical aging

•Hydrolysis

•Crazing (Volynskii crazing)




Resolution of Physical Aging, Crazing, and Hydrolysis

hydrolysis, stress cracking

crazing

time, temperature

alkalinity

surface active model compounds

physical aging




Resolution of the Effects of Aging, Hydrolysis, and Crazing

• The relationship between crazing and bottle failure needs further investigation

• Crazing is sometimes believed to initiate, nucleate, or facilitate hydrolysis (stress cracking), however:

• There often is observed a negative correlation between extent of crazing and bottle failure




Resolution of the Effects of Aging, Hydrolysis, and Crazing

• Jabarin – previous investigations of stress cracking did not separate the effects of crazing and hydrolysis (used alkaline surfactant). 2005 work includes investigation of neutral nonionic surfactants and glycol ether compounds.

• Moskala – investigated stress cracking under conditions very different than what bottles typically see (0.2% NaOH).

• Ecolab – investigation of neutral nonionic surfactants and glycol ether compounds on bottles.



PET - Physical Aging

- Loss of polymer “free volume” below Tg

- Causes PET to become brittle

- Occurs in amorphous, unoriented areas

- Evaluated by DSC (Differential Scanning Calorimetry ) - relaxation endotherm is observed in aged samples

- Evaluated by Physical Property measurement - Strain to failure, i.e. elasticity of the polymer



DSC Relaxation Endotherm





Bottle Burst Testing

• Burst Strength

• Percent Expansion



Physical Property Measurement Agr•TopWave Plastic Pressure Tester (PPT/BR3000)


Percent Volume Expansion to Burst for Aged and Virgin Bottles Agr•TopWave Plastic Pressure Tester

0123456789

0 10 20 30 40 50 60 70 80 90 100

Percent Volume Expansion

Freq

uenc

y

Virgin Bottles

Aged 28 days at100F/85%RH

Relaxation Endotherm = 0.5 J/g

Relaxation Endotherm = 2.2 J/g



Alkalinity and PET Hydrolysis

• More work on this topic is required• Different types of alkalinity behave differently

– Hydroxide solutions will stress crack bottles– It appears that a change must occur for bicarbonate solutions to stress crack

bottles (e.g. become more concentrated and/or change chemically)– Stress cracking can occur with bicarbonate containing solutions that have been

neutralized to near pH 7– Is stress cracking better understood from a perspective of pH (i.e. concentration of

hydroxide ions) or from a perspective of the nucleophilicity of anions (hydroxide > carbonate > bicarbonate)

• This understanding is required to relate results from the “caustic stress crack test” (hydroxide alkalinity) to real life (bicarbonate alkalinity)



PET - Hydrolysis

O

OO

O

O

O

O

O

O

O

O

O

O

O

OH

O

OO

O

OOH

H2O alkalinity

P

P

P P



• May be referred to as Volynskii type crazing• Surface active liquid stabilizes colloidal size

fibrils of oriented polymer, preventing necking• Can be distinguished from stress cracking

(hydrolysis) by SEM analysis

PET - Crazing



SEM: Stress Cracking vs Crazing

Stress cracking (hydrolysis) Crazing




Resolution of Physical Aging, Crazing, and Hydrolysis

none dilute NaOH

none physical aging physical aging plus hydrolysis

surfactant physical aging plus crazing

physical aging plus hydrolysis plus crazing

solvent physical aging plus crazing

physical aging plus hydrolysis plus crazing

alkalinity conditionsu

rface

act

ive

agen

t con

ditio

n

physical polymer chemistry of pet isbt bottle and closure committee

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