as a kind of aliphatic polyester derived from biomass with excellent mechanical strength
biocompatibility and biodegradability
is a kind of green polymers with promising potential application. However
the application of PLA as a commodity polyester has been restricted dramatically because of its brittleness and flammability nature. It is still a great challenge to improve flame retardancy and toughness of PLA simultaneously by a simple blending method. In this work
copolymer ionomer (PCLA-PIU) was prepared by chain extension copolymerization of hydroxyl terminated poly(
ε
-caprolactone) (PCL)
PLA prepolymer and phenylhypophosphate
and then incorporated with ammonium polyphosphate (APP) for synergistic modification of PLA. The ionomer can act as a compatibilizer to enhance the dispersion of APP in PLA matrix because of its PLA segments and phenylhypophosphate groups. The SEM observation shows that the APP particles dispersed in PLA/PCLA-PIU/APP composite has significantly smaller size and uniform dispersity
compared to the PLA/APP
20
. The phenyl hypophosphate groups in the ionomer also has an excellent synergistic effect with APP for improving the flame-retardance of PLA. The flame-retardant properties and mechanism of the PLA and its composites were investigated by LOI
UL-94
Cone calorimeter test
SEM
EDS
Raman spectroscopy
etc
. Compared with neat PLA and PLA/APP
the composite PLA/PCLA-PIU
10
/APP
10
containing 10 wt% of PCLA-PIU and 10 wt% of APP
10
achieves the V-0 rating in UL-94 burning test with limiting oxygen index (LOI) as high as 27.6%. The heat release rate and total heat release of PLA/PCLA-PIU
10
/APP
10
are also reduced significantly to 254.9 kW/m
2
and 55.8 MJ/m
2
respectively. SEM and Raman analysis for char residues after Cone calorimeter test suggest PCLA-PIU and APP had synergistic effect on promoting charring of PLA
which result in compact char residue with high graphitization degree
therefore effectively improving the flame-retardant efficiency. Moreover
the toughness of PLA is improved effectively by the flexible PCL segments of ionomers
resulting in a PLA/PCLA-PIU/APP composite with improved flame retardancy and toughness simultaneously. The mechanical properties test results show that the toughness of the modified PLA (10.3 kJ/m
2
of PLA/PCLA-PIU
10
/APP
10
) is significantly improved compared to those of neat PLA (3.7 kJ/m
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