Foamed composition
The invention relates to a foamed composition comprising a thermoplastic copolyester elastomer, wherein the foamed composition has a relative solution viscosity of at least 4.1 as measured according to ISO 1628-5:2015 and wherein the thermoplastic copolyester elastomer comprises hard segments built up from polyester repeating units derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid or an ester thereof and soft segments being polytetramethylene oxide. The invention also relates to a process for preparing the foamed composition.
1. A foamed thermoplastic elastomer composition comprising:
a thermoplastic copolyester elastomer which comprises hard segments comprised of polybutylene terephthalate and soft segments comprised of polytetramethylene oxide, wherein
the foamed thermoplastic elastomer composition has a density between 0.1 to 0.7 g/cm 3 and a relative solution viscosity (RSV) of at least 4.1 as measured according to ISO 1628-5:2015, and wherein
the foamed thermoplastic elastomer composition has no visible cracks.
2. The foamed thermoplastic elastomer composition according to claim 1 , wherein the thermoplastic copolyester elastomer is present in an amount of at least 70 wt % based on the total weight of the foamed thermoplastic elastomer composition.
3. The foamed thermoplastic elastomer composition according to claim 1 , further comprising a plasticizer in an amount of at most 30 wt % based on the total weight of foamed thermoplastic elastomer composition, and wherein the plasticizer is selected from the group consisting of terephthalates and esters thereof, dibasic acid esters, mellitates and esters thereof, cyclohexanoate esters, citrate esters, phosphate esters, modified vegetable oil esters, benzonate esters, petroleum oils and combinations thereof.
4. The foamed thermoplastic elastomer composition according to claim 1 , wherein the RSV of the foamed thermoplastic elastomer composition is at least 4.2.
5. The foamed thermoplastic elastomer composition according to claim 1 , wherein the foamed thermoplastic elastomer composition is in the form of beads having dimensions of between 1.0 and 10 mm.
6. The foamed thermoplastic elastomer composition according to claim 5 , wherein the beads have dimensions of between 3.0 and 7.0 mm.
7. An article comprising the foamed thermoplastic elastomer composition according to claim 1 .
8. The article according to claim 7 , wherein the article is an inner shoe sole or a shoe midsole.
9. A process for preparing the foamed thermoplastic elastomer composition according to claim 1 , wherein the process comprises the steps of:
(a) providing an unfoamed thermoplastic elastomer composition comprising the thermoplastic copolyester elastomer having hard segments comprised of polybutylene terephthalate and soft segments comprised of polytetramethylene oxide and having an RSV of at least 4.1 as measured according to ISO 1628-5:2015;
(b) bringing the unfoamed thermoplastic elastomer composition to a foaming temperature of between (Tm−100)° C. and Tm, in which Tm is the melting temperature of the polybutylene terephthalate hard segments of the thermoplastic copolyester as measured according to ISO 11357-1:2009 by DSC in the second heating curve, with a heating and cooling rate of 10° C. per min, under nitrogen atmosphere;
(c) providing a physical blowing agent under pressure to the unfoamed thermoplastic elastomer composition; and
(d) releasing the pressure thereby forming the foamed thermoplastic elastomer composition and forming the foamed thermoplastic elastomer composition having a density between 0.1 to 0.7 g/cm 3 and no visible cracks.
10. The process according to claim 9 , wherein the unfoamed thermoplastic elastomer composition comprises the thermoplastic copolyester elastomer in an amount of at least 70 wt % based on the total weight of the unfoamed thermoplastic elastomer composition.