DE4224668C1 - Polyamide mol. wt. increase for rapid reaction in melt - by adding terephthal di:aldehyde or acetal of lower alcohol, e.g. to form recycled polyamide suitable for original purpose after treatment - Google Patents

Abstract

The increase (wt. of polyamide (I) in the melt by) comprises adding 0.1-1 wt.% additive (II) w.r.t. (I), and terephthaldialdehyde (IIA) and/or the acetals of lower alcohols is used as (II). In an example, 25 kg/h polyamide 6 relative soln. viscosity (RSV) = 1.79, 500 mg/100 ml conc. HC1 at 25 deg. C) were melted in an extruder operating at 300 rpm and treated with (A) 0, (B) 0.1, (C) 0.2, (D) 0.4, (E) 0.6 (wt.)% (IIA) (m.pt. 112-115 deg. C). The extruded polyamide had and RSV of (A) 1,79, (B)1.87, (C) 1.93, (D) 2.06, (E) 2.18. USE/ADVANTAGE - The increase may be used with all types of (I), esp. polyamide 6, 6.6, 22, 23, 6.9, 6.10, 6.12 and 6.13. Esp. recycled (I), which are usually degraded during recycling, may be used for the original or similar purposes after treatment. The reaction, which may be carried out in an extruder, is rapid and avoids prolonged thermal loads during processing.

Description

Polyamides are in large quantities in pure form or modified to fibers, plastic molded parts, foils as well as an adjuvant in a variety of applications such as e.g. B. hot melt adhesive used. The polyamide synthesis takes place from lactams via cationic, hydrolytic and anionic build-up reactions and polycondensation of diamines with dicarboxylic acids, aminocarboxylic acids or Derivatives thereof (Viehweg, Müller: Kunststoff-Handbuch, Vol. VI, page 11 ff., Carl-Hanser-Verlag Munich, 1966).

Depending on the process, degrees of polymerization / Molecular weights reached commercial Meet requirements. Higher molecular weights are e.g. B. via thermal post-polycondensation in the solid phase realized.

In DE-OS 38 31 707 a method for accelerated Polyamide production during melt polycondensation using aminocaprolactam and / or Lysine components and with the addition of catalysts, as well also accelerated solid-phase post-polycondensation the catalyst-containing (co) polyamides and the Polyamides produced by the process described.

DE-OS 38 31 708 contains a method for solid phase Post-polycondensation of (co) polyamides, which  small amounts of lysine components and about equivalent ones Amounts of a polycarboxylic acid included. It becomes thermoplastic in a shorter reaction time malleable, slightly branched, aliphatic (co) polyamides with increased melt viscosity and more pronounced Maintain structural viscosity. To appropriate properties response times can still be reached necessary for several hours. The polyamides are in this second, energy-intensive process stage thermal over a longer period of time.

DE-OS 27 02 306 describes a process for the production of polyamides with high viscosity, in the melt state with the addition of an alkylene carbonate in the polyamide mass. This makes a polyamide with a high degree of polycondensation receive.

The object of the invention is therefore a simple and reliable process for quickly increasing the molecular weights to develop polyamides in the melt, which on an industrial scale in a reactor, preferably a reaction extruder is feasible.

The invention thus relates to a method for increasing the molar masses of polyamides in the melt by addition an additive in an amount of 0.1 to 1.0% by weight, based on the polyamide. The process is characterized by that as an additive terephthalaldehyde and / or its acetals of lower alcohols are used.

The amount of additive depends mainly on it to what extent an increase in molecular weight and thus an increase in viscosity is also desirable. A mole Terephthalaldehyde is capable of a maximum of two free  Bind amino groups. Additional additions remain ineffective, unnecessarily increase the Cost and may even worsen the other properties of the polyamide to lead. Therefore, the amount of the additive is preferably so chosen to be less than half a mole per free amino group is added.  

If necessary, the desired optimal amount can also be determined in preliminary tests, so that in technical Scale predictable and reproducible improvements the molecular weights and the viscosity achieved will.

The inventive method can for all types of Polyamides are used, in particular polyamide 6, Polyamide 6.6, polyamide 11 and 12 and polyamide 6.9, 6.10, 6.12 and 6.13.

The method according to the invention is of particular importance for the use of recovered polyamides, because recycling is a thermal burden that generally also to a reduction in the molecular weights and leads to a reduction in viscosity. Recycled polyamides can thus according to the invention for the same or similar Purposes for which they were originally used were used.

The implementation of the polyamides with the invention Additive takes place very quickly, so that additional unnecessarily long thermal stresses avoided during processing can be.

The additive can be added in the usual manner solid or molten state or in an inert Solvent dissolved. Unless low-boiling solvents be used or the acetals of lower Alcohols can be removed in gaseous form. Multi-stage extruders generally also have Degassing zones in which such vapors are removed can.  

The method according to the invention is as follows Examples explained in more detail:

Example 1

Polyamide 6 with a relative solution viscosity η _rel = 1.79 (500 mg / 100 ml, concentrated sulfuric acid, 25 ° C.) was used as the base polymer. 25 kg / h of polyamide 6 were melted in a ZSK-30 / Werner & Pfleiderer extruder and the following amounts of terephthalaldehyde were metered into the melt at 300 rpm. Terephthalaldehyde has a melting point of 112 to 115 ° C. The extruded polyamide was measured again and gave the values shown in Table 1:

Table 1

Example 2

Polyamide 6.6 with a relative solution viscosity η _rel = 1.78 (500 mg / 100 ml, concentrated sulfuric acid, 25 ° C.) was used as the base polymer. The material was mixed with terephthalaldehyde as described in Example 1 and extruded.

The properties are in Table 2 compiled:

Table 2

In experiment No. 10, the solution viscosity could no longer be determined because the polyamide 6.6 is no longer in solution went.  

Experiments 11 to 18 received on January 16, 1993 prove the suitability of acetals of lower alcohols Terephthalaldehyde as an additive.

In experiments 11 to 13, the base polymer is polyamide 6 as used from experiments 1 to 5.

In a ZSK 30 / Werner & Pfleiderer 25 kg / h PA 6 melted and the following at 300 rpm into the melt Additive amounts of terephthalaldehyde tetramethylacetal a melting point of 50-53 ° C metered. Terephthalaldehyde Tetramethylacetal is made according to the instructions of Ernst-Schmitz, chemical reports, year 91, 1958, produced. The properties are in Table 3 compiled.

Table 3

In experiments 14 to 18, the base polymer polyamide 6.6 with a relative solution viscosity η _rel = 1.80 (500 mg / 100 ml · conc. H₂SO₄, 25 ° C) is used.

In a ZSK 30 / Werner & Pfleiderer 25 kg / h PA 6.6 melted and the following at 300 rpm into the melt Additive amounts of terephthalaldehyde tetramethylacetal a melting point of 50-53 ° C metered. The properties are compiled in Table 4.

Table 4

Claims (1)

Process for increasing the molar masses of polyamides in the melt by adding an additive in an amount of 0.1-1% by weight, based on the polyamide, characterized in that terephthalaldehyde and / or its acetals of lower alcohols are used as the additive.