Frequently asked questions

This is a selection of questions that we frequently are asked.

Our first tests with Biomer resins failed

Over the years we experienced the following major processing faults by first users:

1) pellets are not fully molten: the tiny crystallites left act as super-nucleants leading to premature crystallization (parts are crunchy).
2) too long residence time in the dies: the melts starts to crystallize in edges and block the die over time.
3) too long residence time in the hot zones (only on larger machines or at slow speeds): the polymer degrades and melt viscosity decreases.
4) too rapid cooling of the melt: crystallization stops at temperatures below 60C. The melt stays amorphous and clinches to everything.

Is it possible to ease the plastics waste problems with biodegradables?

Recycling probably is the best way to cope with refusal problems. However it is a quite expensive one. Once recyling is well established in a country, biodegradables have but a slim chance to replace classic polymers since alternative disposal systems would have to be established. In developing countries there is a different situation. If biodegradables were introduced before the plastics "explosion" happens they would greatly these countries.

Grinding blocks the mill

PHB is a highly crystalline material with thousands of H-bonds between the crystal helices. As soon as they separate by energy input, the crystals melt. This also occurs by friction during grinding. PHB melts and blocks the mill.
There are two solutions: either freeze the pellets (best with liquid air) and use just tiny aliquots to mill or, better, submerge the mill in liquid air or liquid CO2. The cold liquid transports any friction heat away so that PHB has no chance to melt.

Is it possible to recycle PHB?

PHB can be recycled at last 3 times without any apparent quality deterioration.

We have difficulties solubilizing PHB. What should we do?

PHB is crystalline (this holds for any PHB after storage). For this it is "insoluble". There are two procedures to dissolve it:
1) PHB powder is mixed with chloroform (5 parts of PHB and 95 parts of chloroform) in an explosion proof pressure tube, sealed, and heated for a few minutes to 90C
2) PHB powder is molten for 2-3 min at 190-200C (best between two aluminum foils on two hot plates set to 200C) and then rapidly cooled with liquid air or liquid nitrogen. Molten and immediately frozen PHB stays amorphous for months and years in a deep freezer (-18C or lower). Amorphous PHB dissolved easily.
3) There are rumors that first dissolving PHB in small amounts of trifluoroacetic acid and then diluting the gel in methylene chlorid or chloroform also dissolves crystalline PHB. We have not verified this method.

What do I have to fear if I solubilize PHB in chloroform?

Amorphous PHB, but not crystalline one, is soluble in chloroform (see question above: "We have difficulties solubilizing PHB. What should we do?"). Besides of possibly being intoxicated by the volatile chloroform (a narcotics), you have to know that chloroform is an excellent plasticizer. As such one can not evaporate it totally, even at high vacuum. Please consult the paper of Freier et al. (2001), J. Mat. Sci. Lett. 20, 1929-1931 to avoid misinterpreting the date of (plasticized,) solvent cast films and foils.

There are voids in extrusion

Voids can occur for two reasons: the resin is not fully molten or the resin starts to crystallize prematurely. To avoid reason 1, please increase temperatures in zone 1 and 2 (direction hopper to tip) to 185C and 170C. To avoid reason 2, please do not decrease temperature anywhere to below 140C. The first suggestion avoids that any un-molten remains are pushed into the cooler zones and act there as super efficient nucleants. Premature crystallization occurs if molten material is retarded in some parts of the screw or die where it starts to crystallize. By keeping the temperature at 140C slows down crystallization rate. Please be reminded that crystallization is a function of temperature and time! Please start with the suggestion given above, but later, try to lower temperature setting as described in the link "Processing PHB" since the polyester is not too stable at higher temperatures.

We have difficulties in producing PHB films

There are 3 constraints that spell against blowing films: The first one is melt viscosity. The viscosity is too low to support a bubble. The second is that PHB crystallizes as spherulites that are larger than the film thickness. Then the crystallization extent is such that there practically is no amorphous phase. This in turn means that adhesion of individual spherulites is low and that the films are extremely brittle. We think that there might be ways to settle these questions, but this amounts to a lot of testing.
This holds for blown films. With cast film the situation is different. If done properly, i.e. having the chill rolls set at a temperature so that the material has a mass temperature of about 90C the material starts to crystallize very rapidly (if the proper nucleants are compounded into the material). If then a stretching device is adjusted in a way to align the growing lamellae before they are fixed into spherulites, then uniaxially stretched films with surprisingly high tensile strengths are obtained

What happends if PHB accidently is mixed with classic plastics?

PHB can be blended up to 5% with (recycled) PE or PP or PVC without doing any harm to those. The blends are not prone to degradation since degrading bugs do not have access to the polyester.

How are biodegradable plastics recycled besides composting?

To our knowledge there is no infrastructure to sort used consumer packages into bio and non bio. In Germany sorting is at the customers home: conventional plastics and bio-bin (specific label on packages).

Is it possible to use Biomer resins for consumer packages?

Yes, but keep in mind that packages generally are sold by price.

How comes that there is a biodegradable PE?

Having worked extensively on terminal oxidation of alkanes we know that olefines are oxidized (alkane oxidation by oleo bugs). However this occurs only when the chain length is in the range of natural fatty acids. Photooxidized polyolefines are much, much larger and not biodegraded. Such broken chains are bioinert and thus are not expected to have ecotoxic effects. They simply sit there, invisible, what "biodegradable polyolefine" producer unfortunatly claim as "biodegraded" instead of "erodable" (false labeling!).

What is the best methode to measure the molecular weight?

Basic Setup for GGC columns
Calibration with PS-standard
Column: SHODEX 80 M
Solvent: Chloroform
Concentration: 5 g/l
Pressure: 5 to 8 bar
Flow: 0,5 ml/min
Detector: RI with 1/64xE-5 sensitivity
Detector temp: 50C
Waterbath temp: 47,5 to 48,5C
Solvent eluation: 30 min

Sample size: 15 mg for 3 ml CHCl3
Sample treatment: approx. 1 to 2 min at 85c in a closed tube
Preparation time: 15 to 20 min
Testrun: 30 min
no screenpackage used