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Influence of programming strain/temperature on recovery (PMMA)
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(FYP) Koh Javan
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Programming
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Free recovery upon heating
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by DZ
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Commercial elastic sponge
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Clamped for two days
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Clamped for one month (w/wt heating)
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Clamped for two months
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软泡科普 | 为什么沙发坐久了会塌？揭秘聚氨酯软泡的「记忆疲劳」真相
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压缩永久变形是指软泡在受到外力长期压缩后，去掉压力也无法完全恢复原状的 “残留凹陷” 程度。比如你每天坐在沙发同一位置 8 小时，一年后坐垫凹陷 2 厘米且无法回弹，这 2 厘米的变形量，就是压缩永久变形的直观体现。
行业里通常用百分比衡量：将泡沫样品压缩到一定厚度（如原厚度的 50%），在规定温度（如 70℃）下保持一段时间（如 22 小时），卸载后恢复 30 分钟，测量其残留变形量占原压缩量的比例。比例越低，说明泡沫的 “弹性记忆” 越好，越不容易塌。 |
Slow recovery foam |
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Melamine foam |
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Structure of melamine foam
(2x2x2 mm) (by micro-CT) |
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Zoom-in
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EVA insole |
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PU |
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(Comparison) top: high temperature programming; bottom: room temperature programming.
RVRC biodegradable bag(comparison of programming at room temperature and high temperatures)
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Expansion upon heating after programming via folding |
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Room temperature folding |
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Folded at different temperatures (high temp and room temp)
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Long term stability
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PU foam
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On the effects of long term storage in cold hibernated elastic memory (CHEM) polyurethane foam, Smart Materials and Structures, Vol. 10, No. 2, 2001, pp321-325
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PMMA
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Influence of Long-Term Storage on Shape Memory Performance and Mechanical Behavior of Pre-stretched Commercial Poly(methyl methacrylate) (PMMA), Polymers 2019, 11(12), 1978
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Figure 3. Shape fixity ratio (%) against programming strain. Symbols are used for the individual experimental result, and solid lines of the same color as the symbols indicate the average.
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Figure 4. Shape recovery ratio (%) against programming temperature. Symbols are used for individual experimental result, and solid lines of the same color as the symbols indicate the average.
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Figure 5. Residual strain against programming temperature. Symbols are used for individual experimental result, and solid lines of the same color as the symbols indicate the average.
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Figure 6. Stress versus strain relationship in cyclic uniaxial tension. (Inset of zoom-in view of the small strain range is included if necessary).
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玻璃化转变温度Tg的影响因素 |
2. 交联程度与分子量
交联程度和高分子链的分子量对玻璃化温度有明显影响。交联度增加会提高分子链间的相互作用力，导致玻璃化温度升高。而分子量增大通常会导致玻璃化温度升高，因为长链分子在玻璃态时需要更高的能量才能发生链段运动。
3. 结晶与取向程度
结晶和取向程度是影响玻璃化温度的另外两个重要因素。结晶度高的高分子材料，其分子链排列规整，分子间相互作用强，因此玻璃化温度Tg高。而取向度的增加也会提高玻璃化温度，因为取向会使分子链在某一方向上排列更加紧密。
4. 增塑剂与填料
增塑剂和填料的加入会对玻璃化温度产生影响。增塑剂可以降低分子间的相互作用力，使玻璃化温度Tg降低；而填料的加入可能会提高或降低玻璃化温度，这取决于填料与基体之间的相互作用。
6. 升温速率与冷却速率
升温速率和冷却速率对玻璃化温度的影响主要体现在热分析实验,比如使用差式扫描量热分析法（DSC）测定Tg温度时，较快的升温速率可能导致玻璃化温度测量值偏高，而较快的冷却速率可能导致测量值偏低。因此，在进行热分析时，选择合适的升降温速率非常重要。
7. 微观结构与形态
高分子材料的微观结构和形态对其玻璃化温度有重要影响。例如，晶体结构的形成和晶粒的大小都会影响玻璃化温度的高低。此外，材料的形态如棒状结构、片状结构等也会对玻璃化温度产生影响。
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