Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1995-05-05
1996-08-27
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523124, 525415, 435135, C08L 6700, C08G 6391
Patent
active
055501737
DESCRIPTION:
BRIEF SUMMARY
THIS INVENTION relates to a polymer composition and to oligomers useful as components thereof.
The addition of specific chemical plasticisers may be used to improve the flexibility, the impact strength and extensions to break of polymer mouldings. The free volume theory has been developed to describe the mechanism of polymer plasticisation (Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed. Vol 18, pages 111-185). The addition of an effective plasticising agent leads to an increase in free volume and increased mobility Of the polymer chains. The glass transition temperature represents the change in the amorphous phase from an inelastic glassy material to a more mobile rubbery material. On entering the rubbery phase, this transition is marked by larger increases in the specific volume of the polymer per unit rise in temperature.
Effective plasticisers commonly lower the glass transition temperature of a polymer formulation. A routine measurement for plasticiser effectiveness is the amount by which the glass transition temperature has been depressed from that of the pure polymer for a given incorporation level of the plasticiser.
The typical plasticiser is not a biodegradable material which represents a drawback for plasticisers of biodegradable polymers.
It has now been found that oligomers of very low molecular weight of certain polymers can provide similar benefits when added to a polymer composition.
Thus, according to the present invention there is provided a polymer composition comprising at least one biodegradable microbiologically produced structural polymer (PHA) and at least one oligomer selected from the group: hydroxyalkanoate, lactide, caprolactone and co-oligomers thereof.
The oligomer may be derived from the same polymer as the structural polymer or from a different polymer.
By "structural" is meant shapeable into articles having significant mechanical properties. Such a structural polymer has a weight average molecular weight (Mw) of at least 50000; commonly it is at least 200000 and up to 2.0 million, for example 1.5 million.
In one form of the composition the oligomer has a glass transition temperature (Tg) less by 10.degree. C., especially by 50.degree. to 150.degree. C., than that of the structural polymer. Typically it has Mw of 2000 or less, for example in the range 200 to 1200, but high enough to ensure substantial non-volatility in the structural polymer during melt processing. Thus it should be essentially non-distillable, except possibly under high vacuum. Typically the oligomer is liquid or waxy solid. The oligomer is generally a blend of different short chains, i.e. monomers, dimers, trimers etc. The oligomers may be linear or branched and could contain one or more different monomer units. Therefore, although the Mw may be given as an average, it will in fact be a range of different molecular weights corresponding to the composition of the oligomer. The mutual proportions of the structural polymer and the oligomer are non-statistical, that means they are different from those occurring in structural polymer as prepared. Preferably the content of oligomer in the polymer composition is sufficient to plasticise the PHA, that is, to decrease its Tg by 2.degree. to 50.degree. C., especially 5.degree. to 30.degree. C.
In another form of the composition the oligomer may be used as a filler. Such oligomer has a Tg within 10.degree. C. of that of the PHA. Typically it has a Mw in the range 2000 to 25000, especially 4000 to 20000. Such a composition has a Tg substantially equal to that of the structural polymer alone, and therefore should contain added plasticiser (for example as above) if a lower Tg is required. Whether or not a lower Tg is required, this form of the composition is advantageous for making polymer articles which are required to be more rapidly biodegradable than the structural polymer alone, because the oligomer degrades faster than the usual filler materials and opens the structure to provide a larger surface area for enzymatic degradation of the structural polymer to
REFERENCES:
patent: 5126255 (1992-06-01), Anderson et al.
Bal Jasbinder S.
Hammond Timothy
DeWitt LaVonda R.
Michl Paul R.
Zeneca Limited
LandOfFree
Polyester composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polyester composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polyester composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1056640