关键词: 聚碳酸亚丙酯二醇, 数码烫画, 热塑性聚氨酯热熔胶, 二环己基甲烷二异氰酸酯, 异佛尔酮二异氰酸酯, CO₂基聚氨酯

Abstract:

Objective To improve the recyclability of the traditional petroleum-based polyurethane hot melt adhesives （TPU）， this study aims to prepare an environmentally friendly CO₂-based TPU with high durability， high mechanical properties and high flexibility. The hard segment is dicyclohexylmethane diisocyanate （HMDI）， the soft segment is carbon dioxide-based polypropylene carbonate （PPCD）， and 1， 4-butanediol （BDO） is used as the chain extender. This CO₂-based TPU is used for white ink heat transfer printing on polyester-cotton fabrics.

Method Polypropylene diol polycarbonate （PPCD） was copolymerized with different isocyanates to synthesize polyurethane prepolymers. Following that， chain extender BDO was added for chain extension to prepare carbon dioxide-based thermoplastic polyurethane hot melt adhesive， which was characterized by Fourier transform infrared spectroscopy （FT-IR） and nuclear magnetic resonance hydrogen spectroscopy （¹H-NMR）. Polyurethane hot melt adhesive was selected， suitable for white ink heat transfer printing on polyester-cotton fabrics through screening.

Results It was learnt from the differential scanning calorimetry （DSC） curve graph that the glass transition temperature （-5.6 ℃） of HMDI type TPU was lower than that of MDI type TPU and IPDI type TPU， which makes the adhesive film moderately soft at room temperature. Thermogravimetric analysis （TGA） showed that all three types of CO₂-based TPU had good heat resistance， with their decomposition temperatures higher than the general heat transfer processing temperatures， leading to good thermal stability. The mechanical property test results of CO₂-based TPU demonstrated that the tensile strength （15.557 MPa） and elongation at break （596.137%） of HMDI type polyurethane were between those of diphenylmethane diisocyanate type （MDI） polyurethane and isophorone diisocyanate type （IPDI） polyurethane， and HMDI type polyurethane have both strength and flexibility. Microstructure analysis indicated that HMDI type TPU had a moderate degree of microphase separation. It not only formed sufficient hard segment micro-regions to provide cohesive strength but also maintained the mobility of molecular chain segments， thus better wetting the substrate during bonding. The dry/wet rubbing fastness of HMDI printed fabrics reached grade 4-5. The printed fabrics showed relatively low stiffness， enabling satisfactory fabric softness and wearing comfort.

Conclusion Three types of CO₂-based TPU were successfully prepared using PPCD as the soft segment， IPDI， MDI and HMDI as the hard segments respectively， and BDO as the capping agent. HMDI type TPU proved to be the best comprehensive balance in all key performance aspects. Its glass transition temperature （-5.6 ℃） is moderate， which helps to achieve optimal softness and durability of HMDI type. In terms of mechanical properties， its breaking strength （15.557 MPa） and elongation at break （596.137%） are reasonably matched with Shore A hardness （61）， featuring both excellent bonding strength and the ability to adapt to fabric deformation. The intrinsic mechanism for the balanced performance of HMDI type TPU lies in its moderate microphase separation structure， with the degree of phase separation between MDI type and IPDI type. This structure enables it to better penetrate the substrate during bonding， ensuring bonding reliability. Printed fabrics made of HMDI type CO₂-based TPU performed the best. It has a relatively high dry and wet rubbing fastness and a relatively low stiffness， achieving a unity of wearing comfort and pattern durability.

Key words: polypropylene carbonate diol, digital heat transfer printing, thermoplastic polyurethane hot melt adhesive, dicyclohexylmethane-4, 4'-diisocyanate, isophorone diisocyanate, CO₂-based polyurethane