[GARY®]-Study on comprehensive utilization of waste PMMA Ⅰ

1. Overview of plexiglass

Polymethylmethacrylate (PMMA) is one of the most important transparent polymer materials.Plexiglass is a kind of high transparent and amorphous thermoplastic. It has the best light transmittance among the plastics. The transmittance is as high as 92% – 93%. It can pass through 99% of visible light and 73% of ultraviolet light.The relative density is only 1 / 2 of that of silicon glass, the anti cracking performance is 7-18 times of that of silicon glass, and the mechanical strength and toughness are more than 10 times of that of silicon glass.It has outstanding weather resistance and aging resistance, constant impact strength at low temperature (50-60 ℃) and high temperature (100 ℃), good electrical insulation performance, arc resistance and biocompatibility. It is one of the medical functional polymers.It has good thermoplastic processing performance, easy processing and molding, stable chemical properties, resistance to general chemical corrosion, less effect on low concentration of acid and alkali, and its corner waste is pyrolyzed into methyl methacrylate monomer, which can be recycled and used for polymerization.However, the heat resistance and wear resistance of PMMA are poor.

Plexiglass is mainly used for aircraft cockpit cover and porthole glass, window glass and daylighting body for construction industry, agricultural and forestry greenhouse, stair and house wall guard, sanitary ware, lighting appliances, aquarium undersea tunnel, optical lens and glasses, plastic optical fiber, laser audio-visual light disc, automobile tail lamp, motorcycle windshield and helmet glass, billboard and advertising light box,Display window and cultural relic protection glass, painting substrate, PMMA superfine powder, etc.In recent years, acrylic / glass fiber reinforced sanitary ware series, large format colorful light box, billboard, sample display stand and other products have greatly expanded the application field of plexiglass plate.

Due to aging and mechanical properties, a large number of wastes are produced every year. Although these wastes are not toxic, they are also considered to be harmful to the environment because of their huge volume and difficult degradation under natural conditions.If it can be effectively recycled, it can not only save resources and protect the environment, but also make full use of the regenerated products to form good economic benefits.


2. Recycling of waste PMMA

 Direct utilization of waste PMMA

Recovery of waste PMMA by dissolution and precipitation/

In the process of dissolution and re precipitation, the waste PMMA plastic is recovered by dissolving the waste PMMA in an appropriate solvent, filtering the solution to remove impurities, then precipitating the polymer with an appropriate non solvent, and then washing and drying the obtained pellets;Solvent and non solvent are recovered from the mixture by fractionation.The selection and pairing of solvent and non solvent is the key to dissolve / reprecipitate waste plastics. The solvent and non solvent combinations are toluene / n-hexane, xylene / n-hexane and toluene / water systems, in which toluene / n-hexane is the best.Their ratio is about (1 ∶ 2) – (1 ∶ 4) (volume ratio).In order to avoid that the viscosity of the solution obtained by dissolving the waste plexiglass with the selected solvent is too high to be treated later, its concentration should be controlled at about L, and the maximum should not exceed.

The process of dissolving / reprecipitating to recover PMMA waste is simple and does not destroy the structure of polymer. It has satisfactory polymer yield and recovery rate of solvent and non solvent. Its recycled plastics can be widely used.The quality of the regenerated polymer is similar to that of the new resin.

Dry paint stripping powder made from waste PMMA

The dry paint peeling powder is prepared by grinding waste PMMA into fine particles of 20-50 mesh, then adding 65% aluminum hydroxide, alumina or barium sulfate, or adding unsaturated polyester with 10% – 20% non PMMA, and then grinding them into fine powder of 20-60 mesh.Spraying it on the metal surface can not only effectively remove the paint and other dirt on the metal surface, but also remove the paint and other dirt on some non-metal surfaces.The waste left by peeling paint can be used several times after regrinding.Compared with using inorganic paint stripping powder or solvent to remove the paint and other organic dirt on metal or nonmetal surface, the dry paint stripping powder made of waste PMMA can avoid the damage of metal or nonmetal surface layer and reduce the environmental pollution.

Coating and special adhesive made of waste plexiglass

The waste plexiglass is dissolved in methyl methacrylate, and then added into unsaturated polyester such as 191 #. It can be used to make glass fiber reinforced plastics with light transmittance > 85%, which can be used to build plastic greenhouse, improve crop yield and shorten crop growth cycle.It can also be used as indoor lighting board.

Similarly, the waste plexiglass dissolved in methyl methacrylate or other monomers containing vinyl ester can also be used in the manufacture of coatings.After the coating is applied, the polymerization reaction can be continued under the initiation of ultraviolet or thermal temperature, and a coating with high finish and aging resistance can be formed on the surface of the material.The waste PMMA was dissolved in methyl methacrylate monomer, and then added with methacrylic acid, acrylic acid functional monomer, methyl ethyl ketone peroxide cobalt naphthenate redox initiator and Diethylaniline / N, N-dimethylaniline accelerator, which can be used for bonding metal, polycarboxylate, PMMA and other materials.For example, 30 phr of ground PMMA is dissolved in the mixed monomer of 80 phr of methyl methacrylate, 10 phr of methacrylic acid and 5 phr of acrylic acid, and then 3 phr of Diethylaniline, 1 phr of methyl ethyl peroxide and 1 phr of cobalt naphthenate (6%) are added, which can be used for the bonding of metals, plastics and PMMA.

In addition, the adhesive can be made by dissolving waste PMMA in various soluble solvents.This adhesive, especially for polymethylmethacrylate material itself, has the best effect.And the viscosity of the adhesive can be prepared according to the needs.Commonly used solvents are dichloromethane, trichloromethane, dichloroethane, tetrachloroethane, chlorobenzene and benzylmethylacetone.For example, 5 phr of PMMA is dissolved in 95 phr of chloroform to prepare PMMA adhesive with good cementation.However, it should be noted that under the irradiation of light, dichloromethane can be oxidized by oxygen in the air to generate hydrogen chloride and highly toxic phosgene. Therefore, 1% – 2% ethanol should be added during the manufacturing process to make the generated phosgene react with ethanol to form ethyl carbonate to eliminate its toxicity.

Waste plexiglass as water treatment agent

Waste plexiglass is hydrolyzed in alkaline condition to produce poly (sodium methacrylate), which is a known flocculant for water treatment.It can be used for wastewater treatment, especially for high acidity wastewater treatment.This hydrolysis method is simple and the cost is small.It is reported that in the alkali resistant reactor, isopropanol, sodium hydroxide and water are heated and refluxed until the crushed PMMA is completely hydrolyzed.

Poly (methacryloylhydrazide) can be produced by the reaction of waste PMMA with hydrazine hydrate (hydrazine hydrate) at 120-175 ℃.Poly (methacryloylhydrazide) (PMH) is not only a new type of water treatment agent, but also a selective adsorbent for mercury ion.It is reported in the literature that the water-soluble poly (methacryloylhydrazide) can be obtained by adding 1kg waste PMMA into a autoclave which has been injected with 20L water and hydrazine, dipping for 12 hours at room temperature, and reacting at 150-170 ℃ for 7 hours.

Post time: Jul-21-2021