Table 1.

Conditions under which the ZPP samples were aged.

Sample label	Ageing conditions			Utilised for XPS	Ageing type
	Temperature	Relative humidity	Ageing duration
0	—	—	—	O	Unaged
1	71 °C	0%	4 months	O	Thermal only
2			6 months	—
3			8 months	O
4			12 months	O
5		30%	2 weeks	O	Hygrothermal
6			4 weeks	—
7			8 weeks	O
8			16 weeks	—
9		70%	2 weeks	O
10			4 weeks	—
11			8 weeks	O
12			16 weeks	—
13		100%	2 weeks	O
14			4 weeks	O
15			6 weeks	—
16			12 weeks	O