Polyester. You probably encounter it every day, from your clothes to your water bottles. But this versatile material is far more fascinating than you might think! Let’s dive into the amazing world of polyester, exploring its properties, applications, and the exciting innovations shaping its future.
The Polyester Family:
Polyester isn’t just one thing; it’s a whole family of polymers, created by cleverly linking together molecules to form long chains. This process allows for incredible customization, resulting in materials with a wide range of properties. Think PET (in your soda bottles), PBT (in your electronics), and many more specialized types.
Beyond the Basics: Biodegradable and High-Performance Polyesters:
While traditional polyesters have been around for decades, recent innovations have taken the material to a whole new level. Two exciting areas are biodegradable polyesters and high-performance polyesters.
Biodegradable Polyesters: A Greener Tomorrow:
The environmental impact of plastics is a major concern, and biodegradable polyesters offer a compelling solution. Materials like PLA, PCL, PBS, and PHA can be broken down by microorganisms, reducing plastic pollution and creating a more sustainable future. Imagine packaging that disappears harmlessly after use!
PLA: The Green Plastic Superstar:
PLA, or polylactic acid, is a standout biodegradable polyester. It’s non-toxic, strong, and boasts excellent biocompatibility, making it ideal for everything from food packaging to medical implants. It’s a true “green plastic” champion!
PCL, PBS, and Beyond: A Diverse Family of Biodegradable Wonders:
PCL (polycaprolactone) is another star, known for its flexibility and biocompatibility, often used in drug delivery systems. PBS (polybutylene succinate) offers a good balance of properties and cost-effectiveness, making it a promising material for packaging. And PHA (polyhydroxyalkanoates) is a highly versatile family of biodegradable polyesters with a wide range of potential applications.
High-Performance Polyesters: Pushing the Limits:
On the other end of the spectrum, high-performance polyesters are engineered for exceptional strength, durability, and heat resistance. These materials are finding their way into demanding applications, from automotive parts to advanced electronics.
The Future is Polyester:
The world of polyester is constantly evolving. Scientists are developing new types of polyesters with enhanced properties, improved sustainability, and expanded applications. From biodegradable packaging to high-performance electronics, polyester is shaping a brighter, more sustainable future. So next time you encounter this versatile material, take a moment to appreciate its incredible versatility and the innovative science behind it!
Polyester is a general term for polymers obtained by polycondensation of polyols and polybasic acids. Mainly refers to polyethylene terephthalate ( PET ), but also customarily includes polybutylene terephthalate ( PBT ), polytrimethylene terephthalate ( PTT ), polyethylene terephthalate 1,4- Linear thermoplastic resins such as cyclohexane dimethanol ( PCT ) and polyethylene naphthalate ( PEN ) are a type of engineering plastics with excellent performance and wide range of uses.
With the development of thermoplastic polyester, new varieties are constantly emerging, such as environmentally friendly biodegradable polyester and special high-performance (high strength, high mold, high temperature resistance, etc.) polyester. Biodegradable polyesters include: polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), etc.; high -performance polyesters, mainly liquid crystal polyester, polyarylate, etc.
Biodegradable polyester materials are polyester materials that can be degraded through the action of natural microorganisms (bacteria, fungi, etc.). There are many types of such materials, which can be divided into the following two types according to the production method:
(1) Chemical synthesis of degradable polyester
Mainly refers to polylactic acid (PLA) , polycaprolactone (PCL) , polybutylene succinate (PBS) , polyglycolic acid (PGA) , polypropylene carbonate (PPC) , etc. Obtained through condensation polymerization reaction, chain extension reaction and ring-opening polymerization.
(2) Biological synthesis of degradable polyester
It refers to polyester materials whose raw materials are taken from nature and synthesized using biological fermentation methods, including microbial polyester and microbial polysaccharide. Microbial polyesters mainly include polyhydroxyalkanoates (PHA) , polyhydroxyalkanoic acids (PHAs) , and copolyester PHBV . PHA is mainly poly-3-hydroxybutyric acid (PHB), which is the most widely existing, earliest discovered and most thoroughly researched type of PHA. PHAs refer to poly-hydroxyalkanoic acids composed of C and above segments. PHBV refers to the copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid and its derivatives.
Below, a brief introduction to six biodegradable polyester materials : PLA/PCL/PBS/PPC/PGA/PHA (PHB/PHAs/PHBV).
Polylactic acid PLA
Polylactic acid (PLA), also known as polylactide , is a non-toxic, non-irritating, high-strength, good biocompatibility, biodegradable and absorbable polymer material. It has good plasticity, is easy to process and shape, and does not pollute the environment.
After polylactic acid products are discarded, they can be completely decomposed into CO 2 and H 2 O in soil or water under suitable temperature and humidity conditions under the action of microorganisms, water, acids and alkali, without causing pollution to the environment. It is a completely natural recycling, excellent biocompatibility and biodegradable synthetic polymer material.
As a completely degradable polymer material, polylactic acid is called “green plastic” and is currently the most promising environmentally friendly material.
The raw material for synthesizing polylactic acid is lactic acid . Lactic acid is also known as propanol acid or 2-hydroxypropionic acid. There is an asymmetric carbon atom in the molecule and it is divided into three optical isomers: L type, D type and DL type. There are many methods for producing lactic acid. In industry, there are mainly two methods: starch fermentation method (biological method) and chemical synthesis method .
Fermentation It uses starch extracted from corn, wheat, cassava, sugar beet and other plants as the initial raw material. It is decomposed by enzymes to obtain glucose, which is then fermented by lactic acid bacteria and turned into lactic acid. Most of the lactic acid produced by fermentation is L-form lactic acid. The key to fermentation is the selection of strains. The chemical synthesis method of lactic acid uses acetaldehyde and hydrogen cyanide as raw materials to obtain lactic acid.
The main methods for synthesizing polylactic acid include direct condensation polymerization and ring-opening polymerization.
Direct polycondensation method can be divided into solution polycondensation and melt polycondensation. Although the direct polymerization process is simple, it is difficult to control the molecular weight and it is not easy to obtain high molecular weight polymers.
Lactide ring-opening polymerization is the most well-researched polymerization method so far . Lactide ring-opening polymerization can produce polylactic acid with a relative molecular weight of 100,000 to 1 million.
The density of polylactic acid is 1.25-1.28g/cm3, the melting point is 176°C, and the glass transition temperature is 60-65°C . Polylactic acid has good thermal stability and good solvent resistance, and can be processed in a variety of ways, such as extrusion, spinning, biaxial stretching, and injection blow molding. In addition to being biodegradable, products made of polylactic acid also have biocompatibility, gloss, transparency and good hand feel .
The strength, compressive stress, cushioning, drug resistance, moisture resistance, grease resistance and sealing properties of polylactic acid are superior to existing general plastics such as polyethylene, polypropylene, polystyrene and other materials, and it is recognized by the industry as the most promising One of the most promising new packaging materials.
PolycaprolactonePCL
Polycaprolactone (PCL) is a linear aliphatic polyester obtained by ring-opening polymerization of ε-caprolactone (ε-CL) . It is a semi-crystalline polymer with good thermal stability and a much higher decomposition temperature than other polyesters . It is easily decomposed by microorganisms or enzymes in nature, and the final products are water and carbon dioxide.
Since the 1990s, PCL has received widespread attention internationally and has become a research hotspot due to its superior biodegradability and biocompatibility . PCL has excellent drug passability and mechanical properties, and can be used as a biomedical material, an implant material in the body, and a controlled drug release material. It has been approved by the US FDA.
PCL synthesis usually uses an initiator to initiate ε-CL ring-opening polymerization in bulk or solution. The most commonly used initiator systems include active hydrogen initiating systems, cationic catalysts, anionic catalysts, etc. In addition, ε-CL can also be photoinitiated polymerization, y-ray radiation polymerization, microwave radiation polymerization, etc.
PCL is a semi-crystalline polymer with a melting point of 60°C and a Tg of about -60°C . Its repeating structural unit has five non-polar methylene groups -CH- and a polar ester group. -COO- The CC bonds and CO bonds in the molecular chain can rotate freely. This structure makes PCL very flexible and processable , and can be extruded, injection molded, wire drawn, blown film, etc. In addition, the structural characteristics of PCL also allow it to be copolymerized and blended with many polymers. However, a serious drawback of PCL is that its melting point is very low, only about 60°C. Therefore, it has poor heat deformation resistance .
Polybutylene succinate PBS
Polybutylene succinate (PBS) is obtained by the condensation polymerization of succinic acid and butylene glycol . The resin is milky white, odorless and tasteless, and is easily catabolized by various microorganisms in nature or enzymes in animals and plants. Decomposes into carbon dioxide and water. PBS has good biocompatibility and bioabsorbability and is a typical completely biodegradable polymer material .
PBS entered the field of materials research in the 1990s and quickly became one of the hot materials in general biodegradable plastic research that can be widely promoted and applied. The source of its synthetic raw materials can be either petroleum resources or fermentation of biological resources.
The synthesis methods of aliphatic polyester include biological fermentation and chemical synthesis . The synthesis cost of biological fermentation method is relatively high, and it is rarely reported for PBS. Chemical synthesis methods can carry out molecular design and synthesis of products at lower costs, and mainly include direct esterification method, transesterification method and chain extension method.
The density of PBS is 1.26g/cm, and the melting point is about 114°C. Depending on the molecular weight and molecular weight distribution, the crystallinity of PBS ranges from 40% to 60% . In the mechanical property test, it shows high brittleness and the elongation at break is only about 300%. PBS has good heat resistance, and its heat distortion temperature and product use temperature can exceed 100°C . Research shows that copolymerization modification can reduce the crystallinity of PBS, thereby improving the biodegradation rate and elongation at break.
The thermal properties, processing performance and cost-effectiveness of PBS have unique advantages among degradable plastics. Compared with degradable plastics such as PCL, PHB, and PHA, PBS is extremely cheap ; compared with other biodegradable plastics, PBS has excellent mechanical properties, close to PP and ABS plastics ; it has good heat resistance, with a heat deformation temperature close to 100°C. The final use temperature can exceed 100℃ . PBS overcomes the shortcomings of low heat resistance temperature of other biodegradable plastics; its processing performance is very good, and it can be used for various molding processes on existing general plastic processing equipment. Its processing performance is currently the best among degradable plastics.
Polypropylene carbonate PPC
Polypropylene carbonate (PPC) is a type of aliphatic polycarbonate (APC) and is a biodegradable polyester. Polypropylene carbonate is synthesized from carbon dioxide and propylene oxide . It was first discovered and synthesized by Professor Shohei Inoue of Kyoto University in Japan in 1969.
The properties of polypropylene carbonate are closer to soft rubber than to ordinary thermoplastic resins . The glass transition temperature of polypropylene carbonate is around 30°C, and it will thermally degrade above 200°C .
Due to the presence of ester groups, aliphatic polycarbonate (APC) polymers can be hydrolyzed by lipase and have certain degradation properties. Therefore, polypropylene carbonate can be used in low-temperature (-80°C) plastic wraps for meat products, and Degradable foam materials, plates, disposable tableware, disposable medical and food packaging materials and other fields .
Polyglycolic acid PGA
Polyglycolic acid (PGA, also known as polyglycolic acid) is the simplest structure among biodegradable polymers . Polyglycolic acid is a simple linear aliphatic polyester with a high degree of crystallinity and is a very tough polymer.
Polyglycolic acid is non-toxic and biodegradable. The final degradation products are CO 2 and H 2 O, which will not accumulate in vital organs. Therefore, it has attracted attention in medical materials and biodegradable materials. Polyglycolic acid is the earliest commercialized variety of absorbable polymers in the body . Since the 1970s, a large amount of polyglycolic acid has been used to prepare absorbable surgical sutures .
Usually the synthesis of polyglycolic acid involves direct condensation polymerization and ring-opening polymerization. The direct polycondensation method is the direct dehydration polycondensation of glycolic acid. The polymerization process is simple, but the resulting polyglycolic acid has a small molecular weight and is easy to decompose. To obtain high molecular weight polyglycolic acid, the method of first melt polycondensation and then solid phase polycondensation can be used. High molecular weight polyglycolic acid is usually prepared by ring-opening polymerization of glycolide (a binary cyclic condensation polymer of polyglycolic acid).
Polyglycolic acid has good mechanical properties and a relative molecular mass of more than 10,000. Its strength can fully meet the requirements for the use of absorbable sutures. However, when used in fractures or other internal fixations, the strength is not enough; when the average relative molecular mass reaches At 20000~145000, polyglycolic acid can be drawn into fiber shape.
Polyglycolic acid has the characteristics of high crystallinity and high melting point . Polyglycolic acid is almost insoluble in all organic solvents , but can be dissolved in a mixed solution of phenol and dichlorophenol (10:7) or trichloroacetic acid.
The degradation rate of polyglycolic acid is faster than that of PLA, PCL, etc. , especially the mechanical strength decays quickly . The biodegradation process of polyglycolic acid is indirect . It forms oligomers through the hydrolysis of unstable CO bonds on the main chain, and then further degrades into CO2 and H2O under the action of enzymes.
Polyhydroxyalkanoate PHA
Polyhydroxyalkanoate (PHA) is an intracellular polyester synthesized by many bacteria . At present, about 80 different fatty acids have been found as monomers of PHA in about 300 species of bacteria. The number of carbon atoms in these structural units is 3 to 14, with saturated or unsaturated side chains, aliphatic and aromatic polymers. Sidechains etc. At present, more than 90 genera of bacteria have been found to be able to synthesize more than 150 kinds of PHA with different structures.
PHA is an intracellular energy and carbon source storage substance synthesized by many bacteria under conditions of nutritional imbalance. It is a general term for a type of β-hydroxy aliphatic polyester , including polyhydroxyalkanoate ( PHA ), polyhydroxyl chain Alkanoic acids ( PHAs ), copolyester PHBV .
PHA is mainly poly-3-hydroxybutyric acid (PHB) , which is the most widely existing, earliest discovered and most thoroughly researched type of PHA. PHAs refer to poly-hydroxyalkanoic acids composed of C and above chain segments . PHBV refers to the copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid and its derivatives .
The synthesis methods of polyhydroxyalkanoates include biological synthesis and chemical synthesis. Biosynthesis methods are divided into bacterial synthesis methods and gene synthesis methods. Biodegradable polymers synthesized by biosynthesis methods are mainly polyhydroxyalkanoates (PHA).
The cost of biomanufacturing PHA is much higher than that of polyolefins , mainly due to higher raw material costs and lower production efficiency. In order to reduce the cost of PHA production, cheap carbon sources are currently mainly used to replace glucose and genetically modified plants to produce PHA.
The chemical synthesis method is: the ring-opening polymerization process of β-butyrolactone has two methods: one method is the cleavage of the bond between the carbonyl group and the oxygen atom in the lactone ring; the other method is the β-butyrolactone ring-opening polymerization process. The bond between the carbon atom and the oxygen atom breaks.
The main advantage of PHA is that it can be produced using biotechnological processes , and its product properties can be applied to a wide range of applications. Plastics, films, and even elastomers can be produced from this type of polymer . Blow molding and fiber-grade products are also under development. The polymers are stable even in hot water but biodegrade in water, soil and a combination of both, even under anaerobic conditions .
As a new type of functional material, PHA can be made into films, bottles and injection molded parts. It can also be spun into fibers and made into fabrics. Therefore, it can be widely used in plastic films, orthopedics, personal hygiene products, controlled drug release, special packaging, etc. field. However, due to its higher price, it is more used in the fields of biomedicine and cosmetics.