Page 26 - eBook_Proceedings of the International Conference on Digital Manufacturing V1

Proceedings of the International Conference on Digital Manufacturing –
Volume 1

Despite the small magnitude of change, a non-linear increase
in pH difference percentage was observed over time, particularly
for the Cube samples, which exhibited the highest overall pH
increase (4.60%) by Day 28.

This suggests a gradual accumulation of degradation
byproducts, such as acidic oligomers and monomers (including
lactic acid, the primary hydrolysis product of PLA), which can
lower the local pH and alter the surrounding microenvironment
during the degradation process (Elsawy, Kim, Park & Deep,
2017).

5 4 3.9642 4.6036
pH Difference Percentage (%) 3.5 3 2 2.3047 2.0408 2.9449 2.7167 2.9793 3.0968
4.5
3.3722

2.5
2.9412
2.4051
1.5

0.5
0 1 0 0 0 1.9305
Day 0 Day 7 Day 14 Day 21 Day 28
Time Interval

Cube Dogbone Bar

Figure 4: pH difference percentage of Cube, Dogbone and Bar PLA
samples over a 28-day immersion period in SBF.

In comparison, Dogbone and Bar samples showed lower final
pH variations, peaking at 3.37% and 3.10%, respectively.
Although the ranking in pH variation differs, these trends loosely
correlate with the weight loss results, with the Cube samples
showing the highest increase despite exhibiting the lowest weight
loss. This inconsistency implies that pH change is not solely
dependent on weight degradation, but also possibly influenced by
localised surface degradation and sample geometry affecting the
interaction with the surrounding medium.

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