Polyesters

Thermoplastics > Polyesters

Polyesters
Polyesters types
Thermoplastic Polyesters There’s more to TP polyesters than you think. You may know PET, PBT, and PETG, but what about PEN, PCT, PCTG, PCTA, and PTT. In a general sense, the polyesters are polymers containing carboxylic groups in the chain. The general term polyester, we refer to all polymers obtained by condensation of a polyacid with a polyol. Usually the polyacid is a bifunctional acid and polyalcohol is a bifunctional alcohol (copolymerization). For special applications, only acids or alcohols or poly alcohols functional used in small strictly controlled to not cause a three-dimensional crosslinking with consequent gelation of the polymer mass quantities. in the production phase. Copolymerization offers many advantages, since it is difficult to obtain a homopolymer can only meet a wide range of properties, usually a homopolymer is not characterized by good mechanical properties.
Aliphatic and aromatic
Regarding the starting monomers, polyesters differ in aliphatic and aromatic. The main difference between the two is the presence of benzene rings of the monomeric unit: do not present the aliphatic aromatic structure, while in the repeating unit of the aromatic rings one or more aromatic are present. Depending on the spatial or spatial distribution of atoms, we can distinguish: linear polymers (thermoplastic or thermosetting) obtained by reaction between a dibasic acid and a saturated bifunctional alcohol. Because complete saturation, have a three dimensional structure and, therefore, are thermoplastic and become thermoset for crosslinking. branched polymers The ramifications inhibit biodegradation crosslinked polymers (unsaturated intermediate) obtained by reaction of acids and polyhydric alcohols saturated polyesters They are straight chain thermoplastic polymers, including polyethylene terephthalate unsaturated polyesters contain within them carbon-carbon double (C = C) or triple (C = C)
Aromatic polyesters
Aromatic polyesters are most commonly used because they have excellent mechanical properties, suitable for the production of films and fibers and technical articles. Among the most important we found the terephthalic polyesters. Polyesters containing varying percentages of cyclic oligomers, about 1.5%. The oligoemerinas are considered harmful because they tend to migrate on the surface. Therefore, the amount of oligomers is less and the products of poly (alkylene terephthalate) can be prepared by various methods, but the two routes most exploited synthesis and studied are those involving the reaction of glycols with terephthalic acid (TPA) or dimethyl terephthalate (DMT). PPT - polypropylene terephthalate PEN - polyethylene naphthalate PBN - polybutylene naphthalate PET - polypropylene terephthalate PBT - polypropylene terephthalate PCT - dimethylene terephthalate-policlorohexileno PC - Polycarbonate is an alkyl chain derived from an aromatic diol typically. Polycarbonates are party with many distinctions, polyester resins.
Aliphatic polyesters
Aliphatic polyesters are coupled with polyanhydrides and poly (amino acids), synthetic polymers more hydrolyzable known. Although not suitable for many technical applications where the aromatic polyesters which are readily biodegradable, also having good biocompatibility properties are used. This makes them very interesting both ecological and biomedical field.? The first synthesized aliphatic polyesters are characterized by a low molecular weight and therefore poor mechanical properties for this is mainly used as plasticizers. Aliphatic polymers are more vulnerable to microbial attack of the aromatic. Although it was observed that corresponding aliphatic polyesters are more susceptible than aromatic enzymatic attack, which however have a too low melting and / or suitable mechanical characteristics. Therefore, to improve these properties have been introduced in aliphatic polyesters of aromatic units. Polybutylene succinate PBS Polyethylene succinate PESU Polybutylene succinate adipate PBSA pBad polybutylenadipate PCL polycaprolactone The polyesters were the most promising for the realization of biodegradable products materials, since they have a similar natural polymers and some of them, especially the poly (acids-hydroxy) structure may be fragmented by enzymes produced by microorganisms such as bacteria and fungi the poly (hydroxy acids) are the simplest polyacids glycolic acid PGA and PLLA polyacids L-lactic obtained by polymerization reactions, respectively, for ring opening of lactide and glycolide.
Copolyesters
The copolyester is formed when modifications are made to polyesters, which are combinations of diacids and alcol with diolles. For example, by introducing a diacid, such as terephthalic acid (TPA), with a alcol as 1,4 butanediol and diols, such as poly (tetramethylene ether) glycol (PTMG) the material becomes a copolyester as the TPC ET . The copolyesters retain their strength, clarity and other mechanical properties, if any, against a variety of chemicals usually affect other materials such as polycarbonates. This, plus its versatility and flexibility, allows inexpensive parts as well as critical and expensive components.