Background

Mass-production refers to manufacture of large quantities of a standardized product often using an automated mechanical process. Key features include efficient production of large quantities of identical products that fulfil pre-set quality requirements, and usually comprise detailed design of material and information flows, as well as effective alignment of subprocesses.

One important parameter in the manufacturing of straw is the speed, i.e. bringing the volume/cost at maximum. Existing high-speed extruders can produce up to 300 m/min (1 500 pcs. of 200mm straws/min) of fixed sizes, while commonly used extruders that can produce straws with various diameters and length operate at the speed of 80 to 150 m/min.

Another critical factor in terms of cost efficiency is the quality of the straws, i.e. that minimal amount of scrap is produced during manufacturing. In general, regular samples are taken from the production line, and the straws are evaluated for, e.g., length, diameter, wall thickness and quality factors, such as uniformity of mass and absence of holes. According to the observed deviations, the manufacturing parameters (screw and pulling speed, temperature) are adjusted. For a PP straw, the manufacturing process is regarded stable, enabling one operator to oversee several production lines with virtually no loss in the production capacity due to quality deviations in the products. Generally, 2 to 3% of raw material loss is calculated in straw manufacturing, of which the majority is accounted for in the set-up procedure of the manufacturing line, before the process parameters have stabilized, i.e. granule melting, production speed reached, and end products are uniform.

Finally, in order to be mass-producible, the safety of the product must not be compromised through-out the manufacturing process. The goal is to operate the machinery 24/7.

KEY FEATURE: MASS-PRODUCIBLE

Sulapac® Straw material can be processed with existing extruders. The straw dimensions and quality are comparable to that of the production of polypropylene (PP) straws. Furthermore, the manufacturing of Sulapac Straws can be integrated to automated packaging systems of straws with various sizes.

Criteria

Mass-producibility of Sulapac Straws require that the Sulapac granules can be implemented in the same manner as PP in existing straw production machinery. This comprises that the raw material granules are fed into the machine in the same automated way as PP, and the manufacturing speed should be at least 40 m/min. The amount of service breaks must not exceed those that are experienced with current raw material, i.e. scrap of raw material ≤ 3%, and first-pass yield > 99,99%. The manufacturing process shall be continuous.

In another aspect, the requirement for cleaning, or other maintenance of machinery should not exceed that of PP, and as such not compromise efficiency/total throughput.

Validation

Sulapac material straws were manufactured in an existing PP straw manufacturing plant. Two sizes of straws were manufactured, one with a diameter of 6 mm, and one with a diameter of 9.5mm. The length of both straw sizes was 200mm.

The Sulapac material is provided in the same format as PP granules. Thus, the implementation of Sulapac material did not change the set-up procedure of the straw machine, and the set-up time was found to be identical to that of the conventional raw materials. The amount of raw material scrap during start-up did not differ from that known to be produced with PP.

For the 6mm straw, the machine was operated for 7 h 40 min, and altogether 92 000 straws were manufactured. This corresponds to an over-all manufacturing speed of 40 m/min. During the run there were no breaks that could have been directly accounted to the use of Sulapac material. The test run for 9.5mm straw covered 6 h. During this time, 46 000 straws were manufactured, corresponding to an overall speed of 26 m/min. As for the 6mm straw, no machine down-time due to the material was observed.

In both runs, the machine pressure was constant. No need of extra cleaning was observed; according to the operator, Sulapac material does not require more cleaning than when operated with PP.

For the both straw sizes, the regular quality control at 15 min interval showed consistency of manufacture. The weight of straws remained virtually unchanged: the variation of the 6mm straw was between 1.30 and 1.33g, and for the 9mm straw from 21.20g to 21.50g. The straws’ inner diameter and wall thickness remained unchanged. The straws did not contain any holes, and their visual appearance remained unchanged, having a smooth, homogenous surface.

In conclusion, the test runs showed that Sulapac Straw material does not alter the process of continuous production of straws on existing straw production line. The material performed as well as PP. In this view, it is evident that the process can be further up scaled. The test runs were done in a machine with a 35mm screw; by implementing a bigger screw in a higher-power machine, it is possible to increase the output proportionally. As such, the Sulapac material represents a drop-in solution for routine straw production.

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