Orts et al. [228] compared the crystallinity obtainedusing inverse gas chromatography with the resultsobtained from XRD and DSC. In this method, a column waspacked with diatomaceous silica coated with P(3HB-co-3HV) (7, 21 and 27% HV), and the retention of a “probe”chemical (decane) was tested as a function of tempera-ture. Crystallinities of around 60% for all copolymers wereobserved, which was consistent with XRD results. By con-trast, the crystallinities determined from the heat of fusionshowed a large drop from 59% to 24%. It was found that thedecrease in the heat of fusion with increasing HV contentwas not describing a decrease in crystallinity but insteadwas reflective of a decrease in crystallite size and/or crys-tal perfection. It was also noted that as the HV contentincreases, melting begins at a lower temperature, gettingincreasingly close to room temp. This is likely due to sam-ples of lower HV content crystallizing more readily intohighly ordered crystallites with a relatively large crystalsize. It is also likely that the inclusion of this “other” co-unit in the P(3HB) crystalline phase systematically affectsthe heat of fusion due to defect formation