Preparation and properties of polyethylene-based blended films base on mesoporous nano-SiO2 antioxidant active assembly
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摘要: 以十六烷基三甲溴化铵(CTAB)为模板剂，制备介孔纳米SiO2，以其为载体搭载α-生育酚形成抗氧活性组装体(简称组装体)。以组装体为抗氧活性因子，以低密度聚乙烯(LDPE)为基材，引入线性低密度聚乙烯(LLDPE)、聚烯烃类热塑性弹性体(POE)进行共混改性，并以挤出流延法制备系列控释型抗氧活性膜。通过TEM、XRD、氮气吸附脱附、TGA、力学性能测试和释放性能测试等，研究了LLDPE、POE、α-生育酚、组装体四种添加物对活性膜力学、控释等性能的影响，并研究添加物间协同作用。结果表明，引入添加物令活性膜热加工、力学、控释性能显著提升：α-生育酚搭载于组装体后热分解温度提升70%，利于活性膜热加工；各添加物皆不同程度提升薄膜力学性能，其中，POE及组装体的组合添加具有协同增强作用，薄膜拉伸强度提升率为其他样品2.5倍以上；活性膜控释性能显著，组装体令α-生育酚扩散系数下降45%~47%，薄膜结晶度与α-生育酚释放速率呈负相关，利于活性膜释放调控。所制备活性膜可用于软塑活性包装释放调控，且力学、热加工等性能优于改性前，在功能性活性包装材料领域具有广阔的应用前景。Abstract: The mesoporous nano-SiO2 carrier was prepared with cetyltrimethylammonium bromide (CTAB) that served as template. Then α-tocopherol (α-TCP) was integrated into the carrier to form antioxidant active assembly. Low-density polyethylene (LDPE) active films were prepared by flat extrusion. Linear low-density polyethylene (LLDPE) and polyolefin thermoplastic elastomer (POE) were used as modified resin to regulate the films for better performance. The assembly and α-TCP were introduced into the films, serving as antioxidant active factor. The structure of the nano-SiO2 carrier was studied by TEM, XRD and nitrogen adsorption/desorption apparatus. The thermal stability of the assembly was investigated by thermal gravimetric analysis (TGA). The physical and controlled release properties of the films were determined by mechanical performance test, release performance test, etc. Meanwhile, the additives’ synergistic effects on the films were studied. The results show that the active films’ thermal processing, mechanical and controlled release properties are significantly improved with introduction of the additives. The assembly’s insulating effect leads to thermal resistant temperature of α-TCP, which is integrated into assembly, increase by 70% when compared with the bared α-TCP. As compared with pure LDPE film, the mechanical properties of the active films are significantly improved by the additives. The tensile strength increase rate of the film modified by POE and assembly is more than 2.5 times as other samples’. As compared with the films modified with the bared α-TCP, the assembly reduces the diffusion coefficient of α-TCP by 45%-47%, which shows the remarkable controlled release property of the active films. The films’ crystallinity is negatively correlated with release rate of the antioxidant substance. As a result, the prepared materials can be used to regulate active substances’ release rate of antioxidant active package. And it shows a good potential for strengthing and toughing package films.
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图 1 介孔纳米SiO2载体的小角X射线衍射曲线
Figure 1. Small-angle XRD curve of mesoporous nano-SiO2 carrier
图 2 介孔纳米SiO2载体MCM-41孔形(a)和孔道(b)的TEM图像
Figure 2. TEM images of mesoporous nano-SiO2 carrier MCM-41 pore shape (a) and canal (b)
图 3 介孔纳米SiO2载体MCM-41的氮气吸附/脱附曲线(a)及孔径分布曲线(b)
Figure 3. N2 adsorption/desorption curve (a) and pore size distribution curve (b) of mesoporous nano-carrier MCM-4
图 4 α-生育酚、介孔纳米SiO2载体MCM-41和抗氧活性组装体的TG (a)和DTG (b)曲线
Figure 4. TG (a) and DTG (b) curves of α-TCP, mesoporous nano-SiO2 carrier MCM-41 and antioxidant active assembly
图 5 薄膜表面和截面SEM图像：(a) 1Assembly/99LDPE表面；(b) 1Assembly/69LDPE-30LLDPE表面；(c) 1Assembly/69LDPE-30POE 表面；(d) 1Assembly/99LDPE截面；(e) 1Assembly/69LDPE-30LLDPE截面；(f) 1Assembly/69LDPE-30POE 截面；(g) 1α-TCP/99LDPE 截面; (h) 1α-TCP/69LDPE-30LLDPE截面
Figure 5. SEM images of surface and cross section of films: (a) 1Assembly/99LDPE surface; (b) 1Assembly/69LDPE-30LLDPE surface; (c) 1Assembly/69LDPE-30POE surface; (d) 1Assembly/99LDPE section; (e) 1Assembly/ 69LDPE-30LLDPE section; (f) 1Assembly/69LDPE-30POE Section; (g) 1α-TCP/99LDPE section; (h) 1α-TCP/69LDPE-30LLDPE
图 7 LDPE基体(a)和LDPE共混基体(b)薄膜的FTIR图谱
Figure 7. FTIR spectra of LDPE-based (a) and LDPE blends-based (b) films
图 8 未添加α-生育酚或组装体的薄膜(a)、LDPE基体(b)和LDPE共混物基体(c)薄膜的DSC曲线
Figure 8. DSC curves of the film without α-tocopherol or assembly (a)，LDPE-based (b) and LDPE blends-based (c) films
图 10 LDPE基体(a)和LDPE共混基体(b)薄膜中α-生育酚释放实际值及理论趋势曲线
Figure 10. Actual value and theoretical trend curves of alpha-tocopherol release in LDPE-based (a) and LDPE blends-based (b) films
表 1 薄膜配方
Table 1. Formula of films
Sample α-TCP/g Assembly/g LDPE/g LLDPE/g POE/g LDPE 0 0 200 0 0 0.25α-TCP/99.75LDPE 0.5 0 199.5 0 0 1α-TCP/99LDPE 2 0 198 0 0 1Assembly/99LDPE 0 2 198 0 0 70LDPE-30LLDPE 0 0 140 60 0 0.25α-TCP/69.75LDPE-30LLDPE 0.5 0 139.5 60 0 1α-TCP/69LDPE-30LLDPE 2 0 138 60 0 1Assembly/69LDPE-30LLDPE 0 2 138 60 0 70LDPE-30POE 0 0 140 0 60 1Assembly/69LDPE-30POE 0 2 138 0 60 Notes: α-TCP—α-tocopherol; Antioxidant active assembly (referred as Assembly)—Mesoporous nano-SiO2 that carried α-TCP; LDPE—Low-density polyethylene; LLDPE—Linear low-density polyethylene; POE—Polyolefin thermoplastic elastomer; All 10 formulations above were used to prepare extruded films in this study. 
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表 2 不同活性膜DSC结果对比
Table 2. Comparison of DSC results of different films
Sample Tm/℃ $\Delta {H_{\rm{m}}}$/(J·g−1) ${\chi _{\rm{c}}}$/% Transmittance/% Haze/10−4 WP/(10−15cm3· cm·cm−2·s·Pa) OP/(10−13cm3·
cm·cm−2·s·Pa)LDPE(Control group) 109.22 54.81 19.80 90.87 5.28 9.64±0.93 1.88±0.07 0.25α-TCP/99.75LDPE 111.07 56.35 20.35 90.27 5.61 5.06±1.25 1.98±0.07 1α-TCP/99LDPE 111.14 53.33 19.26 90.82 5.44 7.88±0.45 2.01±0.01 1Assembly/99LDPE 111.48 58.22 21.03 90.42 5.47 7.65±0.74 2.06±0.02 70LDPE-30LLDPE 111.90 54.00 20.24 91.45 6.44 7.31±0.47 1.94±0.06 0.25α-TCP/69.75LDPE-30LLDPE 113.21 56.33 21.77 91.30 5.18 6.78±0.94 2.12±0.08 1α-TCP/69LDPE-30LLDPE 112.02 52.16 21.47 91.48 5.77 6.69±0.75 2.04±0.05 1Assembly/69LDPE-30LLDPE 112.81 57.07 22.06 91.55 7.34 7.05±0.74 2.16±0.03 70LDPE-30POE 109.54 41.30 14.91 92.48 3.98 8.87±0.42 4.30±0.13 1Assembly/70LDPE-30POE 109.91 47.82 17.27 91.13 9.96 10.36±0.51 4.76±0.04 Notes: Tm—Melting temperature of films; $\Delta {H_{\rm{m}}}$—Melting enthalpy of films; ${\chi _{\rm{c}}}$—Crystallinity of films; WP—Water vapor permeability of films; OP—Oxygen permeability of films.
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表 3 相对LDPE组的不同薄膜拉伸强度和断裂伸长率变化率对比
Table 3. Change rates of tensile strength and elongation at break for different films in contrast to group LDPE
Sample Tensile strength change rate/% Elongation change rate/% LDPE(Control group) 0 0 70LDPE-30LLDPE 13.6 33.1 70LDPE-30POE 20.7 19.6 1Assembly/99LDPE 12.1 −4.5 1Assembly/69LDPE-30LLDPE 30.9 29.5 1Assembly/69LDPE-30POE 76.2 53.0 Note: Tensile strength and elongation of group LDPE are 18.97 MPa and 513.14%, respectively
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表 4 活性膜厚度Lp及α-生育酚扩散系数D对比
Table 4. Comparison of active film thickness Lp and α-TCP diffusion coefficient D
Sample 0.25α-TCP/
99.75LDPE1α-TCP/
99LDPE1Assembly/
99LDPE0.25α-TCP/
69.75LDPE-
30LLDPE1α-TCP/
69LDPE-
30LLDPE1Assembly/
69LDPE-
30LLDPE1Assembly/
69LDPE-
30POELp/μm 82.1±1.4 86.3±1.5 82.9±1.1 86.1±1.1 84.0±1.0 84.1±1.7 81.4±0.6 D/(10−9 cm2s−1) 3.1861 3.2998 1.6901 2.9468 3.0019 1.6048 2.0134
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