BioPBS / PHA Injection Molding Trial for Degassing Valve

Overview & Project Objective

Objective to produce a 100% biodegradable resealable flexible coffee stand up pouch by replacing the current non-degradable LDPE degassing valve with a blend of biodegradable BioPBS and PHA resin. The film used for the coffee bag is BioPBS.
This one-way degassing valve allows natural coffee gases and CO2 to be evacuated from the coffee pouch/package while not allowing oxygen and moisture to enter the package. This airtight heat seal provides superior protection for product freshness while adding to shelf life.

The two resins that will be blended are BioPBS™ polybutylene succinate (PBS), an aliphatic polyester resin made from succinic acid and 1,4-butanediol and PHA short for poly-hydroxy-alkanoate polyesters produced in nature by numerous microorganisms. Both these resins are 100% biodegradable, excluding a very small amount of necessary stabilizers.

The degassing valves are injection molded in a 64-cavity mold originally designed for LDPE. The challenge is that our BioPBS™ resin is more rigid than the current LDPE. The melt flow rate is lower, while the density/specific gravity is higher.
These factors resulted in a 100% BioPBS™ degassing valve deforming/warping when ejected from the mold. Tabs that hold the degassing membrane in the valve were bent and would not hold the membrane in place under pressure.
Flexibility and melt flow of the BioPBS needed to increase to successfully eject the valve from the mold without deforming the tabs.
A PHA grade will be blended with BioPBS to increase flex modulus and melt flow, while maintaining full biodegradability.

A very extensive molding trial was conducted blending 3 grades of PHA at several loading levels with BioPBS™.
15 different molding conditions were tested, varying cooling, hold time as well as shot weight.
The best process condition resulted in almost 100% flat tabs and a 32% reduction in cycle time!
Other than a very slight tab(s) deformation, all parts ejected well from the stationary/ cavity side of the mold.
All 64 cavities filled accurately, proven by correct part weight based on specific gravity.

Blending PHA with BioPBS™ showed a significant improvement over 100% BioPBS.
The valves molded with PHA resulted in the flattest tabs.
Testing was conducted and it was confirmed that these BioPBS™/PHA valves performed well.
The degassing valve tabs were able to hold the membrane securely in place under pressure when in use.
The BioPBS™/PHA valves have been attached to the BioPBS™ coffee bags, filled with coffee and are now under a 30-day test to evaluate coffee freshness and flavor.

By replacing the LDPE degassing valve, the entire coffee pouch/package is now fully biodegradable
Both BioPBS™ and PHA are both Home Compostable therefore the degassing valve allows the whole coffee package to be Home Compostable which means it will break down into CO2 and H2O and minerals within 365 days
After the coffee pouches pass in-house testing, field testing at customers will begin.

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