PETG raw materials

PETG raw materials: characteristics and applications of high-performance copolyester materials

PETG (Polyethylene terephthalate cyclohexanedimethanol ester) is a non crystalline thermoplastic polyester material modified by ternary copolymerization of terephthalic acid (PTA), ethylene glycol (EG), and cyclohexanedimethanol (CHDM). As an important modified variety of PET, PETG has broken through the performance limitations of traditional PET with its excellent transparency, flexibility, processability, and environmental friendliness. It has demonstrated unique advantages in packaging, medical, construction, consumer electronics, and other fields, becoming a rapidly developing high-performance and high molecular weight material in recent years.

1、 Molecular Structure and Core Characteristics

The molecular structure of PETG is the root of its performance advantages. Compared with crystalline PET, PETG introduces cyclohexanedimethanol (CHDM) monomer into the molecular chain, replacing some ethylene glycol, breaking the regular arrangement of PET molecular chains, significantly reducing crystallization ability, and forming amorphous or low crystallinity structures. This molecular design brings a series of excellent characteristics.

Transparency is one of the most outstanding properties of PETG, with a light transmittance of over 90%, haze below 1%, high glossiness, and comparable to transparent materials such as polycarbonate (PC) and acrylic (PMMA). The amorphous structure avoids the light scattering caused by PET crystallization, and can maintain high transparency even in thick walled products, solving the problems of easy whitening and decreased transparency in ordinary PET thick walled products.

In terms of mechanical properties, PETG has both good toughness and rigidity. Its impact strength is 3-5 times that of ordinary PET, and its notch impact strength can reach over 60kJ/m ², far higher than brittle ordinary PET; At the same time, the tensile strength reaches 30-50MPa and the bending modulus is 1500-2500MPa, which can meet the mechanical requirements of most structural components. PETG has excellent flexibility, with a fracture elongation of up to 200% -300%. It can be processed by cold bending, folding, etc. without breaking, making it suitable for making products that require a certain degree of elasticity.

In terms of thermal performance, the glass transition temperature (Tg) of PETG is about 78-88 ℃. Although it is lower than the crystallization melting point of PET, its thermal deformation temperature is relatively high (65-75 ℃), and it can be used stably at room temperature for a long time. It also has outstanding low-temperature resistance and maintains good toughness at -40 ℃ without brittleness. Compared with PC, PETG has a lower processing temperature (usually 230-270 ℃), lower energy consumption, and is less prone to high-temperature degradation.

In terms of chemical stability, PETG has good resistance to water, acid, alkali, etc., and its chemical corrosion resistance is better than PMMA and PC. It is not easily corroded by daily chemicals such as alcohol and detergents, and its surface has good scratch resistance, with a hardness of Shore D78-85, which can be further improved by coating. At the same time, PETG is odorless, non-toxic, and meets food contact material standards such as FDA and EU 10/2011. It has also passed medical grade certifications such as USP Class VI, and its safety has been widely recognized.

Processing performance is another major advantage of PETG. As an amorphous material, PETG has good melt flowability, low molding shrinkage rate (0.5% -1.5%), excellent dimensional stability, and is suitable for precision molding. It can be processed through various processes such as injection molding, extrusion, blow molding, and thermoforming, and has a wide processing window that is not prone to stress cracking. It has good post-processing properties (such as printing, bonding, and welding) and can meet the production needs of complex products.

2、 Production process and raw material sources

The production process of PETG is based on polyester polymerization technology, with the core being the precise control of the ratio and polymerization process of ternary monomers to achieve molecular structure regulation. Its main raw materials include terephthalic acid (PTA), ethylene glycol (EG), and cyclohexanedimethanol (CHDM), among which the purity and proportion of CHDM directly affect the performance of PETG.

In terms of raw material sources, traditional PETG's PTA and EG mainly come from the petrochemical industry chain and are produced through processes such as naphtha cracking; CHDM is produced through steps such as cyclohexane oxidation and hydrogenation, and also relies on fossil resources. In recent years, breakthroughs have been made in the research and development of bio based raw materials, and the industrialization of bio based PTA (produced through biomass fermentation), bio based EG, and bio based CHDM has gradually advanced, providing the possibility for green production of PETG and significantly reducing the carbon footprint of products.

The production process of PETG mainly includes three core stages: esterification, copolymerization and polymerization, and granulation. In the esterification stage, PTA first undergoes esterification reaction with EG and CHDM at 180-220 ℃ and 0.2-0.5MPa to produce dihydroxyethyl terephthalate, cyclohexanedimethanol terephthalate, and water. The reaction is accelerated by a catalyst (such as a titanium based catalyst) and the water is removed in a timely manner to promote the forward reaction. The esterification rate needs to reach over 95%.

The copolymerization and condensation stage is based on the esterification product, heated to 240-270 ℃, and carried out in a vacuum environment (pressure ≤ 100Pa) for condensation reaction, by removing small molecule products (mainly EG) to increase the molecular chain. At this stage, it is necessary to strictly control the proportion of CHDM added (usually 30% -50% of the total amount of diols). If the proportion is too high, it will reduce the heat resistance of the material, and if it is too low, it will not effectively damage the crystallinity. The time and temperature of the condensation reaction directly affect the intrinsic viscosity (IV value) of PETG, which is generally controlled between 0.7-1.2 dL/g to balance processability and mechanical properties.

After polymerization is completed, the molten PETG is cast and cut into white or transparent granular slices, which need to be strictly dried (moisture content ≤ 0.005%) to avoid molecular weight loss due to hydrolysis during subsequent processing. According to application requirements, antioxidants, lubricants, UV absorbers and other additives can be added during the granulation stage to improve the thermal stability, processability and weather resistance of the product. The selection of additives should comply with food contact or medical grade standards.

During the production process, advanced online monitoring technologies such as infrared spectroscopy and viscosity meters are required to monitor reaction progress and product performance in real-time, ensuring batch stability. Compared with PET, the polymerization process of PETG requires higher equipment accuracy and process control, especially the measurement and dispersion uniformity of CHDM, which directly affects the transparency and mechanical performance consistency of the product.

3、 Classification and performance differences

According to the characteristic viscosity, CHDM content, and application scenarios, PETG can be divided into multiple categories, and different types of PETG have differences in performance to meet diverse needs.

Classified by intrinsic viscosity (IV value), PETG with low IV value (0.7-0.9dL/g) has good flowability and is suitable for injection molding small precision products (such as cosmetic bottle caps and electronic accessories); Medium IV value PETG (0.9-1.1dL/g) balances fluidity and mechanical properties, suitable for blow molding (such as bottles), extruded sheets, etc; High IV value PETG (1.1-1.2dL/g) has high mechanical strength and is suitable for making structural components such as thick walled plates and pipes.

Classified by CHDM content, PETG with low CHDM content (30% -40%) retains a certain tendency towards crystallization, has slightly higher heat resistance (Tg about 85-90 ℃), good rigidity, and is suitable for packaging products that require heat resistance; PETG with high CHDM content (40% -50%) has more significant non crystallinity, better flexibility and transparency, but slightly lower heat resistance (Tg of about 75-80 ℃), making it suitable for products such as films and hoses that require high toughness.

Classified by application field, packaging grade PETG focuses on transparency, chemical resistance, and processability, meeting the hygiene requirements of food and cosmetic packaging; Medical grade PETG needs to pass biocompatibility certification (such as USP Class VI), be non-toxic, resistant to sterilization (such as gamma ray sterilization), and suitable for medical device production; Industrial grade PETG focuses on mechanical properties and dimensional stability, and is used for structural components in fields such as construction and electronics.

The performance differences of different types of PETG are mainly reflected in heat resistance, flexibility, and processability. For example, the transmittance of packaging grade PETG is usually greater than 92%, the haze is less than 1%, the tensile strength is 35-45MPa, and the elongation at break is 200% -300%; Medical grade PETG not only meets mechanical properties, but also needs to pass cytotoxicity and sensitization tests; The thermal deformation temperature (0.45MPa) of industrial grade PETG can reach 60-70 ℃, which is suitable for structural support requirements at room temperature.

4、 Diversified application areas

PETG, with its comprehensive performance advantages, has replaced traditional materials in multiple fields and demonstrated broad application prospects, especially in scenarios with high requirements for transparency, toughness, and environmental friendliness.

The packaging field is PETG's core application market, especially occupying an important position in high-end packaging. In cosmetics packaging, the bottles and hoses made of PETG have a crystal like transparent texture, high gloss, which can highlight the product grade, and have excellent chemical resistance. They can contain skin care products, perfume and other products with complex ingredients. At the same time, they have strong impact resistance, are not easily broken, and reduce transport losses.

In the field of food packaging, PETG meets the standards for food contact materials (such as FDA 21 CFR 177.1310), has no odor, and is resistant to low temperatures (suitable for refrigeration). It can be used to make food cans, beverage cups, freshness boxes, etc. Its good sealing and chemical resistance can protect the flavor of food, and its transparency makes it easy for consumers to observe the contents. PETG film can be made into composite packaging film and shrink film, with good heat sealing properties, suitable for irregular packaging.

In the field of healthcare, medical grade PETG has become an ideal material for medical devices due to its good biocompatibility, sterilization resistance, and ease of processing. It can be used to make infusion sets, syringe shells, medical catheters, drug packaging bottles, etc. Its transparency facilitates the observation of liquid flow status, and its resistance to gamma ray sterilization ensures the sterility of medical supplies. In addition, PETG is also used to make dental models, prosthetic shells, etc., balancing comfort and durability.

In the field of architecture and decoration, PETG panels are used to make lighting panels, protective covers, decorative panels, etc. due to their high transparency, weather resistance, and impact resistance. Compared with glass, PETG sheet is lighter in weight (density 1.23-1.27g/cm ³, about half of glass), less prone to breakage, and has higher safety; Compared with acrylic, PETG has better chemical resistance, is less prone to yellowing and aging, and has a longer service life. PETG can also be made into decorative films and furniture veneers, achieving diverse appearances through printing, coating and other processes.

In the field of consumer electronics, PETG is used to make electronic device casings, protective covers, display screen frames, etc. Its good dimensional stability and processability can meet the production requirements of precision components, and its wear resistance and scratch resistance can be improved through surface treatment (such as hardened coatings). In 3C product packaging, PETG vacuum formed boxes can clearly display products and provide good cushioning protection.

In other fields, PETG film can be used for printing, hot stamping, anti-counterfeiting labels, etc., with excellent post-processing performance; PETG pipes are used for industrial fluid transportation and medical device pipelines due to their good flexibility and chemical corrosion resistance; In the field of toys, transparent toys made of PETG are safe, non-toxic, and have strong impact resistance, making them suitable for children's use.

5、 Environmental Protection and Development Trends

The environmental characteristics of PETG give it an advantage in the trend of sustainable development, while the industry is constantly promoting technological innovation, expanding its performance boundaries and application scenarios.

In terms of environmental protection, PETG has good recyclability, and waste PETG products can be recycled through physical or chemical recycling. Physical recycling is the process of sorting, cleaning, and crushing waste materials before melting and reshaping them. Recycled PETG can be used to produce non food contact products (such as packaging materials and industrial components); Chemical recycling decomposes PETG into monomers through depolymerization reaction, which are reused in polymerization production to achieve closed-loop circulation. Compared with chlorinated plastics such as PVC, PETG does not produce toxic gases during combustion and has lower environmental risks.

The research and development of bio based PETG is an important direction for green development. By adopting bio based PTA, bio based EG, and bio based CHDM, the dependence on fossil resources can be significantly reduced, and the carbon emissions of products during their lifecycle can be reduced by more than 30% compared to traditional PETG. At present, multiple companies have launched some bio based PETG products. With the reduction of bio based raw material costs, the industrialization of fully bio based PETG will accelerate.

The development trend of PETG is mainly reflected in three directions: high performance, functionalization, and application expansion. In terms of high performance, by optimizing the CHDM ratio through molecular design, introducing fourth monomers (such as long-chain diols) or composite with nanomaterials (such as graphene and nano calcium carbonate), the heat resistance (such as thermal deformation temperature exceeding 80 ℃), wear resistance, and mechanical strength of PETG are improved, expanding to the field of engineering structural components.

In terms of functionalization, develop PETG varieties with special functions, such as antibacterial PETG (adding antibacterial agents such as nano silver and zinc ions) for medical and food packaging, which can inhibit microbial growth; Flame retardant PETG meets the fire protection requirements in the fields of electronics and construction by adding halogen-free flame retardants; Intelligent response PETG (such as temperature sensitive color change and pH response) is used for high-end packaging and medical monitoring to achieve dynamic regulation of functions.

In terms of application expansion, PETG has enormous potential in the field of new energy, such as the production of transparent backplates for photovoltaic modules (with excellent weather resistance and insulation); In the field of 3D printing, PETG wire has become one of the preferred materials for FDM printing due to its high printing accuracy and resistance to warping. It can be used to create complex models and functional components; In the field of flexible electronics, PETG film can be used as a substrate and combined with conductive materials to prepare flexible circuits and sensors.

In terms of technological innovation, optimizing the continuous polymerization process can improve the production efficiency and quality stability of PETG, and reduce production costs; The development of new catalysts (such as non antimony based environmentally friendly catalysts) can reduce heavy metal residues and improve product safety; Blending modification technology (such as PETG blending with PC and PMMA) can integrate the advantages of various materials to develop composite products with more comprehensive performance.

As a high-performance copolymer polyester material, PETG's development reflects the progress of polymer material modification technology. By precise regulation of molecular structure, PETG breaks through the performance limitations of traditional polyesters, maintaining excellent transparency and processability while also possessing flexibility, environmental friendliness, and safety. With the advancement of green manufacturing technology and the expansion of application scenarios, PETG will play an increasingly important role in high-end manufacturing, sustainable packaging, and medical health, becoming one of the key materials driving the upgrading of the polymer materials industry.