# Heat-Resistant Behavior of PLA/PMMA Transparent Blends Induced by Nucleating Agents
## 3 Results and Discussion  
### Melting and Crystallization Behavior  
The PLA and blends were subjected to DSC to assess the compatibility of the polymers and evaluate the influence of the PMMA and nucleating agent on the PLA crystallization performance. This helped clarify the crystallization process, nucleation mechanism, and overall performance regulation of the PLA blends. The heating curves of the PLA blends at various temperatures are depicted in Figure 1. Each PLA/PMMA exhibited only one Tg, indicating the absence of macroscopic phase separation and confirming excellent compatibility between the PLA and PMMA, which was consistent with the findings of existing studies [21]. The Tg of the PLA/PMMA blends exposed to isothermal crystallization at different temperatures increased slightly since the
Furthermore, no significant changes were evident in the DSC curves at different temperatures when only the nucleating agent was added to the PLA, suggesting that the nucleating agent minimally impacted PLA crystallization in these conditions. Adding the nucleating agent and PMMA simultaneously facilitated a substantial change in the Tm of the blends. PLA/PMMA/TMC-300 displayed the highest Tm, which exceeded that of the PLA/PMMA, while the Tm of the PLA/PMMA/TMC-328 was lower. As shown in Table 2, the \(\mathrm{X_{c}}\) of the PLA decreased from 31.9% to 26.2% and 22.3%, respectively, at 80 \({}^{\circ}\)C and 100 \({}^{\circ}\)C after adding PMMA. This reduction in crystallinity occurs because PMMA is an amorphous polymer, while PLA requires the arrangement of its molecular chains in a more regular manner via chain movement during crystallization. The uniform PMMA and PLA mixing impeded the movement of PLA molecular chains, inhibiting PLA crystallization. A higher pretreatment temperature decreased the  
Figure 1: The DSC heating curves of the PLA blends after 96 min, 29 min, and 5 min of isothermal crystallization at (**a**) 80 \({}^{\circ}\)C, (**b**) 90 \({}^{\circ}\)C, and (**c**) 100 \({}^{\circ}\)C.  
isothermal crystallization time, reducing the molecular chain movement times and the subsequent crystallinity. After adding the TMC-300 and TMC-328 nucleating agents to the system, the \(\mathrm{X_{c}}\) of the blends increased, particularly at 100 \({}^{\circ}\)C, since heterogeneous nucleation provided more nucleation sites during the crystallization process and promoted molecule self-assembly into nano-scale fibrous crystals. However, due to the inhibitory effect of the PMMA segments on PLA crystallization, the crystallinity remained lower than that of pure PLA, even with the nucleating agent promoting nucleation. The exothermic characteristics and crystallization kinetics of PLA blends were analyzed to clarify the impact of various nucleating agents and PMMA on isothermal PLA crystallization. As shown in Figure 2, the analysis of the results revealed that the crystallization peaks of different blends were either small or absent after crystallization at 80 \({}^{\circ}\)C for 1 h, indicating that PLA crystallization was not initiated or displayed relatively low crystallinity at this temperature. However, clear crystallization peaks were observed at 90 \({}^{\circ}\)C and 100 \({}^{\circ}\)C, with a particularly pronounced peak intensity at 100 \({}^{\circ}\)C. The increased mobility of the PLA molecular chains at 100 \({}^{\circ}\)C allowed the PLA to easily surpass the energy barrier and facilitate crystallization. Based on the thermal characteristic curves shown in Figure 2b,c, the relative crystallinity of the various different components in different conditions was calculated using the following formula [22]:  
\[\mathrm{X_{t}}=\frac{X_{C}(t)}{X_{C}(t_{\infty})}=\frac{\int_{0}^{t}(dH_{T}/d_{ t})d_{t}}{\int_{0}^{\infty}(dH_{C}/d_{t})d_{t}} \tag{3}\]  
where t is the crystallization time, and \(dH_{C}/d_{t}\) is the heat flow rate.