Research Progress of Biodegradable Hot Melt Adhesive (Part Two)

The polylactic acid used in the matrix resin used in this invention may include poly-L-lactic acid, poly-D-lactic acid or a mixture of both, the polylactic acid undergoes direct polycondensation under heating and high vacuum conditions, and an appropriate catalyst is added to promote the esterification reaction and transesterification reaction. Finally, a biodegradable hot melt adhesive with excellent properties was synthesized by a two-step process. M.Viljanmaa, A studied the adhesive properties and stability of PLA hot melt adhesives in the use of packaging materials. The hot melt adhesive was polylactide (PLLA): polycaprolactone (PCL) = 81:1 mixed, one sample was capped with acetic anhydride to the hydroxyl end, and the other sample was not Protection, using traditional EVA hot-melt adhesives without degradation characteristics as a performance reference, the gel chromatography (GPC) was used to determine the molecular weight and crystallinity of the copolymers before and after degradation, and the adhesive strength and cross-sectional morphology of the authors' adhesives were evaluated. The tests were also conducted separately. It was found that both types of gels degraded within a predetermined time, and the hot melt adhesives that had undergone the end-capping reaction degraded slowly.

M.Viljanmaa, A also studied the properties (such as exposure time, curing time, thermal adhesiveness, viscoelasticity, and weightlessness) of this biodegradable hot melt adhesive. The authors found the stability of the hot melt adhesive. Poorly affecting its use, but after a certain chemical treatment will significantly improve its stability. The use of acetic anhydride for capping will significantly increase its dimensional stability. In addition, there are many reports on the research of polylactic acid biodegradable hot melt adhesives [.

2.2 Polyester amide (PEA) hot melt adhesive Polyester amide combines the advantages of both polyester and polyamide. It is a new type of hot melt adhesive base material. The ester and amide bonds in the polymer can be used in acid-base catalysis. Under the hydrolysis, and then under the microbial, enzyme-catalyzed degradation. In recent years, a large number of effective research results have been achieved in the synthesis of polyester amides. Liu Xiaobo of the Chengdu Institute of Organic Chemistry has developed a series of novel polyester amide copolymers, mainly including ε-caprolactone and DL-lactic acid. Polyester amides are synthesized by direct esterification of glycolide chains with long chain structures and amide diols with aliphatic dibasic acids. On this basis, the polyester amide copolymers copolymerized with amide diols, aliphatic diols and dicarboxylic acids have been developed, opening up new fields for the application of the polymers.

Grigat Ernst has invented a polyester amide hot melt adhesive component, which is a low molecular weight polyester with a molecular weight (Mn) of 800 to 1300 that is a polycondensation of ethylene glycol/butylene glycol and ethylene glycol, and then 1,6- The diisocyanate reacts to synthesize polyester amide, and then it is compounded with an appropriate amount of plasticizer and flame retardant. Finally, a completely biodegradable hot melt adhesive can be synthesized for bonding leather and paper. Timmermann Ralf synthesizes polyesteramides with 30%-70% of a copolymerized polyester of an aliphatic dicarboxylic acid and a dicarboxylic acid and 70%-30% of an amide diol to obtain a biodegradable hot melt adhesive. .

2.3 Polyhydroxyalkanoates Hot melt adhesives Polyhydroxyalkanoates are biopolymers that are present in microbial cells and have biological activity and complete biodegradability. They can be used as matrix resins for biodegradable hot melt adhesives. In order to improve its performance and reduce costs, other polymer materials are generally used for modification. In the study of biodegradable hot melt adhesives, polyhydroxybutyrate/valerate copolymer (PHBV) was the most. KauffmanThomas et al. invented a biodegradable hot melt adhesive, which is synthesized from 20% to 90% 3-hydroxybutyric acid and 9% to 35% 3-hydroxyvaleric acid, and 10% to 80% of the ring and ball softening point. It is a polar tackifier at 60°C (ASTME-26), 0-50% plasticizer, 0-30% paraffin, 0-3% stabilizer, and the hot melt adhesive thus synthesized can not only be completely biological Degradation, and provide a way out for the current oil crisis.

2.4 Natural Polymer Biodegradable Hot Melt Adhesives Hot melt adhesives made of natural polymers have been increasingly used in the research of hot melt adhesives. Many natural polymers such as lignin, starch, and bark have been used. Among them, starch is not only fully biodegradable, but also has a wide variety of sources, low natural resources, and natural renewable resources. Therefore, starch is most widely used in the development of biodegradable hot melt adhesives. LovineCarmine et al.] added 0 to 20% starch to the polylactic acid component to prepare a biodegradable hot melt adhesive. Jauregui Beloqui et al. invented a biodegradable hot melt adhesive prepared by mixing starch with EVA copolymers. Moreover, the adhesive performance is not reduced compared with ordinary hot melt adhesives. This hot melt adhesive can be used to bond many materials (such as paper, fibers, plastics, etc.), as a sealant and repair agent. Steinwinfried and others use glutinglue and plasticizers and other fillers to make biodegradable hot-melt adhesives with low melting point, which can be used to bond paper, wood, and foam plastics, and can be widely used in the packaging field. Ishiguro Hideyuki and others used 100 parts of natural rosin, 20 to 150 parts of natural rubber and 20 to 100 parts of plant/animal wax to make a completely natural polymer hot melt adhesive, which can be completely biodegraded. In addition, other biodegradable hot melt adhesives (such as aliphatic polyesters, vinyl alcohol-vinyl acetate copolymers, and sucrose benzoates as matrix resins) have also been reported.

3 Conclusion <br>Biodegradable hot melt adhesive is a very promising adhesive, the main drawback is the use of poor stability, bonding strength needs to be further improved. With the increasing awareness of environmental protection, the demand for environmentally friendly materials has also greatly increased. There are many researches on biodegradable hot-melt adhesives in foreign countries, which have not been reported so far in China. Therefore, the adhesive industry should take a long-term view and actively invest in the research of biodegradable hot melt adhesives, and make its own contribution to the sustainable development of the country.



Authors: Yin Jinjie, Ma Haiyun, Wang Lin (Liaoning Technical University