Preparation and properties of grafted polyacrylic acid modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate) antioxidant film
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摘要: 脂质氧化将导致食品变质，因此开展抗氧包装膜的研究十分重要。本文以丙烯酸(AA)为金属螯合配体，以聚(3-羟基丁酸酯-co-3-羟基戊酸酯)(PHBV)为基材，通过紫外光接枝的方法将AA接枝聚合到PHBV薄膜表面，制得具备金属螯合能力的PHBV-g-PAA非释放型抗氧化膜，研究接枝时间对PHBV-g-PAA复合膜形貌结构、Cu2+螯合量和力学性能的影响。结果表明：通过傅里叶变换红外光谱仪与水接触角测试仪对复合膜进行结构表征，证明了聚丙烯酸(PAA)成功接枝到PHBV薄膜表面；通过SEM观察复合膜形貌结构发现，随着接枝时间的延长，接枝产物密度逐渐增大，接枝时间为20 min时，薄膜表面PAA接枝层的致密均匀性最佳；通过DSC和XRD测试复合膜结晶性能表明，结晶度从未接枝的63.97%下降至56.23%，有利于提高薄膜的韧性，接枝20 min时薄膜的韧性最好；采用甲苯胺蓝(TBO)染色法和火焰原子吸收光谱法测定复合膜表面羧基密度和Cu2+螯合量，当羧基密度为392.65 nmol/cm2时，对应的Cu2+螯合量为115.09 nmol/cm2，两者之比接近4，表明可以生成稳定的五元环螯合结构，从而起到抗氧化的作用；通过力学性能测试发现，接枝后薄膜拉伸强度和断裂伸长率均呈现先上升后下降的趋势，接枝20 min时拉伸强度和断裂伸长率分别提升27.51%和99.02%。所制备非释放型抗氧化膜的Cu2+螯合能力及力学性能均优于PHBV薄膜，在食品包装领域具有广阔的应用前景。
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关键词:
- 聚(3-羟基丁酸酯-co-3-羟基戊酸酯) /
- 丙烯酸 /
- 光接枝 /
- 金属螯合 /
- 抗氧化
Abstract: To reduce the need to add metal chelators to lipid-based foods to prevent their oxidation, antioxidant packaging is receiving increasing attention. In this study, acrylic acid (AA) was used as the metal chelating ligand and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was used as the substrate. AA was covalently immobi-lised onto the surface of PHBV films by UV grafting to produce the non-releasing PHBV-g-PAA anti-oxidant film with metal chelating ability. The results show that the successful grafting of polyacrylic acid (PAA) onto the surface of PHBV films was demonstrated by structural tests on the composite films. Observation of the composite film morphology and structure by SEM revealed that the density of graft products gradually increased as the grafting time increased. When the grafting time was 20 minutes, the dense uniformity of the PAA grafted layer on the film surface was the best. The crystalline properties of the composite film were tested by DSC and XRD. It showed that the crystallinity decreased from 63.97% to 56.23%, which was conducive to improving the toughness of the film, and the best toughness of the film was achieved at 20 minutes of grafting. Toluidine blue (TBO) staining and flame atomic absorption spectrometry were used to determine the carboxyl density and Cu2+ chelation on the surface of the composite membrane. When the carboxyl density was 392.65 nmol/cm2, the corresponding Cu2+ chelating amount was 115.09 nmol/cm2. The ratio of the two was close to 4, indicating that a stable five-membered ring chelating structure could be generated, thus acting as an antioxidant. Through the mechanical properties test, it was found that the tensile strength and elongation at break of the grafted films both increased first and then decreased. Tensile strength and elongation at break increased by 27.51% and 99.02% respectively at 20 minutes of grafting. The Cu2+ chelating ability and mechanical properties of the prepared non-release antioxidant film are better than those of the PHBV film, which has promising applications in the food packaging field. -
图 1 聚(3-羟基丁酸酯-co-3-羟基戊酸酯)(PHBV)薄膜紫外(UV)光接枝反应过程
Figure 1. Ultra violet (UV) light grafting reaction process of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) film
h—Planck constant; v—Frequency; PAA—Polyacrylic acid
图 2 接枝时间对PHBV-g-聚丙烯酸(PAA)复合膜表面组分的影响
Figure 2. Effect of grafting time on surface composition of PHBV-g-polyacrylic acid (PAA) composite membrane
图 3 接枝时间对PHBV-g-PAA复合膜表面和截面形貌的影响：((a)~(d)) 接枝时间为0 min、10 min、20 min、30 min的表面形貌图；((e)~(h)) 接枝时间为0 min、10 min、20 min、30 min的截面形貌图
Figure 3. Effect of grafting time on the surface and cross-sectional morphology of PHBV-g-PAA composite membranes: ((a)-(d)) Surface topographies of grafting time of 0 min, 10 min, 20 min and 30 min; ((e)-(h)) Cross-sectional topography of the grafting time of 0 min, 10 min, 20 min and 30 min
图 4 接枝时间对PHBV-g-PAA复合膜晶体结构的影响
Figure 4. Effect of grafting time on crystal structure of PHBV-g-PAA composite film
图 5 不同接枝时间PHBV-g-PAA复合膜的DSC曲线：(a) 二次升温；(b) 降温
Figure 5. DSC curves of PHBV-g-PAA composite films with different grafting time: (a) Secondary heating; (b) Cooling
图 6 接枝时间t对PHBV-g-PAA复合膜表面水接触角的影响
Figure 6. Effect of grafting time t on water contact angle of PHBV-g-PAA composite film surface
图 7 接枝时间t对PHBV-g-PAA复合膜表面羧基含量的影响
Figure 7. Effect of grafting time t on carboxyl content on the surface of PHBV-g-PAA composite membrane
图 8 甲苯胺蓝(TBO)染色前后PHBV-g-PAA复合膜表面颜色变化
Figure 8. Surface color change of PHBV-g-PAA composite film before and after toluidine blue (TBO) staining
图 9 接枝时间t对PHBV-g-PAA复合膜拉伸强度和断裂伸长率的影响
Figure 9. Effect of grafting time t on tensile strength and elongation at break of PHBV-g-PAA composite film
表 1 复合膜的DSC参数
Table 1. DSC parameters of composite membrane
t/min $ {{T}}_{\text{c}} $/℃ $ {{T}}_{\text{m1}} $/℃ $ {{T}}_{\text{m2}} $/℃ ${{\Delta }{H} }_{\text{m} }$/(J·g−1) $ {{X}}_{\text{c}} $/% 0 75.12 165.78 171.23 93.78 63.97 5 84.34 162.84 170.33 93.35 63.68 10 86.65 163.05 171.65 92.48 63.08 15 88.08 162.67 171.08 91.15 62.18 20 91.46 163.15 171.25 87.06 59.39 25 86.57 158.36 168.42 85.21 58.12 30 80.55 153.65 164.34 82.44 56.23 Notes: t—Grafting time; $ {{T}}_{\text{c}} $—Crystallization temperature; $ {{T}}_{\text{m}} $—Melting temperature of films; ${{\Delta }{H} }_{\text{m} }$—Melting enthalpy of films; $ {{X}}_{\text{c}} $—Crystallinity of films. 
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表 2 复合膜表面羧基含量和Cu2+螯合量的比值
Table 2. Ratio of carboxyl content to Cu2+ chelation on the surface of composite membrane
t/min D/(nmol·cm−2) C/(nmol·cm−2) R 0 0.00 0.00 — 5 55.57±2.41 14.90±2.49 3.73 10 183.38±16.54 47.18±4.28 3.89 15 309.73±18.79 87.89±7.16 3.52 20 392.65±27.69 115.09±7.53 3.41 25 435.18±23.96 134.96±11.95 3.23 30 496.28±46.50 155.45±21.80 3.19 Notes: D—Density of carboxyl groups on the surface of the composite film; C—Amount of Cu2+ chelated; R—Ratio of the density of carboxyl groups on the surface of the composite film to the amount of Cu2+ chelated.
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