In terms of yarns, fibers and textiles, there are roughly three categories when it comes to biodegradability: natural materials, bioplastics and plastics made from petrochemicals.
Natural fibers, like jute, hemp or cotton, usually are biodegradable thanks to their natural, cellulose based origin. Viscose based materials (viscose rayon, cupro or lyocell), which are artificially altered in their chemical structure but still originating from cellulose, are usually biodegradable as well. However, considering the "green aspect" of biodegradability, viscose based materials are not the most suitable if one focuses on the environmental aspect of a product beforehand. This is due to viscose based materials requiring production steps involving sulphuric acid and other chemicals that are usually not considered very eco-friendly.
Bioplastics are plastics that originate from renewable biomass, thus not derived from fossil resources. Despite the prefix "bio-", one still needs to pay attention when it comes to bioplastics as it does not automatically mean they are better absorbed by the environment than petrochemical based plastics. So it is that not all bioplastics are biodegradable or quicker composted than "synthetic plastic". A point that is important to tackle for those bioplastics that are biodegradable is to clarify under which circumstances (temperature etc.) they decompose. When it comes to bioplastics, those deriving from starch are usually biodegradable.
Plastics originating from petrochemicals / fossil resources can also be biodegradable. One of the more popular examples are the polyester Polyethylene Terphthalate PET or Polyvinyl Alcohol PVAL PVOH.
BIOABSORBABLE POLYMERS FOR MEDICAL APPLICATIONS
- Polylactic Acid PLA
PLA is prepared from cylic diester of lactic acid by ring opening polymerization. Lactic acid exists as tow optical isomers. Fibers spun from L-polylactide (melting point at 170°C) have high crystallinity when drawn whereas fibers spun from poly DL-lactide are amorphous.
Crystalline poly-L-lactide more resistant to hydrolytic degradation than the amorphous DL form. The rate of poly-L-lactide degradation has been increased by plasticization with triethyl citrate, but this produced a less crystalline, more flexible material.
Time required for poly-L-lactide implants to be absorbed is relatively long and depends on polymer quality, processing conditions, implant site, and physical dimensions of the implant. Absorption time of about 1.5 years for 50 to 90 mg samples of radiolabelled poly-DL-lactide implanted in the abdominal walls of rats. Pure poly-L-lactide bone plates attached to sheep femora showed mechanical deterioration but little evidence of mass loss after four years. In the case of the radiolabelled implants, metabolism resulted in excretion primarily via respiration (CO2).
High molecular weight polymer can be prepared. Fiber samples with large tensile strength are available, by hot-drawing filaments spun from solution. Exposure of polylactic acid to gamma radiation has been shown to result in a decrease in molecular weight.
- Polyglycolic Acid PGA
Unlike PLA (absorbed slowly), PGA is absorbed within a few months postimplantation due to greater hydrolytic susceptibility. In vitro experiments have shown an effect on degradation by enzymes, buffer, pH, annealing treatments, and gamma irradiation.
Since PGA is susceptibility to degradation from moisture and gamma rays, use low humidity ethylene oxide gas sterilization procedures and moisture-proof packaging. Acceleration of in vivo degradation due to gamma irradiation has been exploited to create devices where early fragmentation is desired.
- co-polymer PLA / PGA
Copolymers of PGA/PLA can be tailored for a variety of application. Like 90% PGA / 10% PLA: Braided absorbable suture is similar to PGA. Both absorb between 90 and 120 days post implant. Vicryl retained strength slightly longer and was absorbed sooner than polyglycolide. Differences probably due to differences in polymer morphology because the amorphous regions of poly(lactide-co-glycolide) are more susceptible to hydrolytic attack than the crystalline regions. Like pure PGA and pure PLA, the 90/10 PGA/PLA is also weakened by gamma irradiation.
Copolymers are amorphous between the compositional range 25 to 70 mole percent glycolide. Pure polyglycolide is about 50% crystalline, whereas pure poly-L-lactide is reported to be about 37% crystalline.
- Polycaprolactone PCL
Polycaprolactone is synthesized from e-caprolactone. This semi-crystalline polymer absorbed very slowly in vivo and released e-hydroxycaproic acid as the sole metabolite. Nonenzymatic bulk hydrolysis of ester linkages followed by fragmentation and release of oligomeric species. Fragments ultimately scavenged by macrophages and giant cells. Amorphous regions of the polymer are degraded prior to breakdown of the crystalline regions.
Copolymers of e-caprolactone and L-lactide are elastomeric when prepared from 25% e-caprolactone, 75% L-lactide and rigid when prepared from 10% e-caprolactone, 90% L-lactide.
- Polyhydroxybutyrate PHB
Poly-b-hydroxybutyrate (PHB) is a rare example of a biodegradable polymer that both occurs in nature and can easily be synthesized in vitro. Synthetic PHB, however, has not shown the stereoregularity found in the natural product. High MW, crystalline, and optically active PHB has been extracted from bacteria. This polymer is melt processable and has been proposed for use as absorbable suture.
However, recent improvements in the extraction process have resulted in renewed interest in PHB for both medical and nonmedical applications. Copolymers of hydroxybutyrate and hydroxyvalerate (Biopol) have been developed to provide a wide variety of mechanical properties and more rapid degradation than can be achieved with pure PHB.
In general, an understanding of polymer morphology and crystallization behavior is important for optimization of processing conditions to achieve specific performance characteristics. Investigations into the morphology and crystallinity of Biopol copolymers have revealed isodimorphism, i.e. two crystalline phases were detected in the polymers each containing both types of repeating units.
- Polydioxanone PDS PDO
Fibers made from polymers containing a high percentage of polyglycolide are too stiff for monofilament suture and thus are available only in braided form above the micro-suture size range. The first clinically tested mono-filament synthetic absorbable suture was made from Polydioxanone PDS. The monomer p-dioxanone, is analogous to glycolide but yields a poly-(ether-ester).
Polydioxanone monofilaments retained tensile strength longer than the braided polyglycolide and were absorbed in about six months with minimal tissue response. Polydioxanone degradation in vitro was affected by gamma irradiation dosage but not substantially by the presence of enzymes.
BIODEGRADABLE YARN AND FIBERS
Depending on your end application and amongst others, Swicofil offers products like:
... as well as other products like natural fibers and more. Browse our products or contact us with your project requirements in order to get your perfect yarn or fibers that are made out of biodegradable raw material.