Isolating and removing PLA from textile fibre mixtures

Applicant: NOOSA
Inventors: Hélène L'EBRELLEC, Faraj HAJAR 
Patent application number: WO2023/126480
Title: Method for isolating fibers polylactic acid-based from a mixture of textile fibers and recovery of the latter no longer containing polylactic acid

Mechanical recycling of textiles consists of a series of cutting and fraying steps to return a textile to its fibre state. The fibre obtained can then be spun again (converted into yarn) and then converted back into fabric (knitted or woven). This fibre can also be used as a filler (e.g. a mat), or it can be converted into a non-woven fabric if its quality is too poor to be re-spun, a drawback that should be avoided as far as possible.
Mixed textile fibres are a major obstacle to mechanical recycling. This is because mechanical recycling does not allow the different types of fibres to be separated, the composition of the recycled product obtained will be very difficult to control and, consequently, its properties and quality will also be very difficult to control. It should be noted that elastane is the main obstacle to mechanical recycling; above 8% elastane in the composition of a fabric, fraying is compromised.

Chemical recycling is the partial or complete depolymerisation of the polymers that make up textile fibres. The monomers or oligomers obtained can be used as such or reused in the synthesis of new polymers. The limitation of chemical recycling is that a dissolution step is required prior to the depolymerisation reaction. This dissolution is responsible for chain scissions, which lead to a reduction in the degree of polymerisation or molecular weight. Molecular weight is related to the mechanical properties of a textile fibre. A reduction in molecular weight results in a loss of toughness and elasticity. The fibres obtained after chemical recycling have degraded mechanical properties, which usually requires the addition of a percentage of "virgin" fibres to ensure the properties of the final textile article. In general, this percentage is higher than 40% for cellulosic fibres (textile fibres composed of cellulose) and 20% for polyester fibres.

There is therefore a need to develop recycling solutions for textiles made up of a mixture of fibres, without causing excessive damage to the fibres in the mixture, so that they can be reused in a new textile article.

There are two major challenges related to the management of the end-of-life of textiles. The first relates to textiles that can be reconverted into starting monomers, such as polymeric textiles that are virtually a single material (see patent document WO2021 148549 for the PLA polymer), while the second relates to the way in which textile fibres can be recovered without damaging them excessively, so that they can be reprocessed. 

The applicant has now found that these two challenges can be addressed in a single process, particularly in the context of textiles formed from a mixture of fibres comprising non-PLA textile fibres and textile fibres containing PLA.
 

The combined process of the present invention comprises treating the textile fibres to isolate PLA-containing textile fibres from other non-PLA textile fibres in order to treat remaining but undamaged non-PLA textile fibres for respinning. This step comprises dissolving PLA in a solvent, such as a solvent selected from alkyl lactates. Thus, according to the invention, a method is provided for treating a mixture of textile fibres comprising non-PLA textile fibres and textile fibres containing PLA, characterised in that it comprises the following steps

introducing the mixture of textile fibres into a tank, introducing a predetermined amount of PLA solvent into the tank, dissolving the PLA containing textile fibres, washing the non-PLA textile fibres with the solvent of the PLA, recovering the solution formed of the PLA, and recovering the solution formed by the PLA solvent and the dissolved PLA-containing textile fibres recovering the non-PLA textile fibres for treatment for recarding and respinning separating the non-PLA textile fibres and the undissolved PLA-containing textile fibres from the solution formed by the PLA solvent and the dissolved PLA-containing textile fibres, on the one hand, non-PLA textile fibres and textile fibres containing undissolved PLA and, on the other hand, the solution formed by the PLA solvent and textile fibres containing dissolved PLA.

Preferably, the non-PLA textile fibres are natural fibres.

• According to the present invention, the addition of PLA solvent to obtain a mass ratio between the mass of PLA and the mass of PLA solvent of between 0.06 and 0.09 at a temperature of between 100 and 130°C makes it possible to solubilise textile fibres containing PLA without degrading non-PLA textile fibres. In fact, the other polymers contained in the blend of non-PLA textile fibres, constituents of the third polymer textile fibres, are sensitive to hydrolysis and/or alcoholysis.
• When these third polymer textile fibres enter the depolymerisation reaction medium, i.e. from the treatment step to recover the lactic acid from the solution formed by the PLA solvent and the textile fibres containing dissolved PLA, their molecular structure is modified and consequently their physico-chemical properties, which make them suitable also for textile applications.
• By recovering them quickly, after dissolving the PLA through a solid/liquid separation process, but before the treatment to recover the lactic acid (depolymerisation of the PLA), their properties are preserved and a new use of the polymer of the third fibres can be envisaged, such as textiles for a new textile or other application.
• The advantage of separating the other textile fibres before depolymerisation according to the present invention is therefore twofold. This has the advantage of achieving a rapid and significant dissolution of the PLA.
• In a particular embodiment of the present invention, the PLA solvent used to wash the non-PLA textile fibres after the solid-liquid separation is enriched in residual PLA and recovered to be subjected to a treatment to recover lactic acid. This has the advantage of reducing the amount of residual PLA in the non-PLA textile fibres. A further advantage is that the amount of dissolved PLA is increased, resulting in an increase in the amount of lactic acid recovered after treatment.
• In an advantageous embodiment according to the present invention, the recovered non-PLA textile fibres are subjected to a non-PLA textile fibre treatment before being recarded and rethreaded, comprising rinsing the non-PLA textile fibres arranged to remove residual solvent, using an aqueous solution, and drying the rinsed non-PLA textile fibres.
• Rinsing with an aqueous solution cleans the non-PLA textile fibres by removing the residual solvent used to dissolve the PLA. This rinsing combined with drying can in some cases yield a fine powder containing PLA. This powder can then be isolated to obtain purified non-PLA textile fibres which can be recarded and rethreaded.
• Advantageously, according to the present invention, the method further comprises a step of decontaminating the mixture of textile fibres before introducing the PLA solvent into the mixture of textile fibres. This has the advantage of reducing possible contaminants and processing only a mixture of textile fibres comprising non-PLA textile fibres and textile fibres containing PLA. A decontamination step may be, for example, washing in an aqueous solution. Advantageously, according to the present invention, the step of drying the mixture of decontaminated textile fibres is carried out in a ventilated atmosphere.