ADDITIVES | IMPACT MODIFIERS
processors with a way of precisely adjusting the relative viscosity of polyamides. “This newly developed modifier thus allows the upcycling of high-viscosity polyamide scrap to produce quality injection moulding grade material and offers compounders significant cost benefits over the use of virgin polymers,” the company says. What can be achieved, Brüggemann says, is “a
material that has the desired relative viscosity as well as mechanical properties that are on the same level as those of virgin polyamide injection mould- ing grades. With their high stiffness, tensile strength and impact strength, these upcycled materials are suitable for the same applications as virgin material of corresponding viscosity.” Typical mechanical improvements are shown in Figure 2. Bruggolen TP-M1417 is supplied as dust-free
granules that can be metered accurately. It is easy to process and compatible with the polyamide matrix, making it ideal for compounding applica- tions, according to the supplier.
Figure 1:
Notched Izod impact strength against temperature of NY-6-ATBN copolymers at four different ATBN
contents in PA6 – 0, 7, 13 and 20 wt%
Source: CVC Thermoset Specialties
9 8 7 6 5 4 3 2 1 0
No break
20% 13% 7% 0%
Another claimed benefit of the additive, which
was introduced last year, is that it can be used to modify the relative viscosity of virgin polyamide. Brüggemann says polymer manufacturers can tailor relative viscosities during the compounding stage without having the burden of product change-over on a continuous polymerisation plant. This results in a significant gain in flexibility, the company claims, and can also considerably reduce the amount of off-spec material.
Copolymer options Elastomer producer Kraton Corporation high- lights the use of its Kraton block copolymers to modify polypropylene to provide an alternative to PVC in medical applications. The company says the medical industry has traditionally used plasticised PVC in IV bags and tubing due to its flexibility, transparency and low cost. However, some phtha- late plasticisers used in PVC can leach out in use, albeit in very low quantities. There are also issues around recycling plasti-
-40 -30 -20 -10 0 10 20 Temperature (˚C) 30
cised PVC as, although diethylhexylphthalate (DEHP) is widely used to plasticise PVC for medical applications, it is banned in many countries for use in other applications. “In recent years, there has been an increased demand for PVC-free solutions, such as Kraton’s hydrogenated styrenic block copolymers (HSBC),” says a Kraton representative. HSBCs are used extensively in medical devices for their processability, clarity, flexibility, resilience, strength and durability, according to Kraton. “The new Kraton MD1646 offers the benefits of HSBC and more. Its enhanced rubber segment (ERS) structure gives it a softer feature and excellent compatibility with PP,” the spokesperson says. “When blended with polypropylene random copolymer (PPR), the low polystyrene content results in high elastic recovery, low hysteresis and good kink resistance. Thanks to its high melt flow, the polymer requires lower processing tempera- ture and energy consumption, both for compound- ing and processing.” Kraton MD1646 and RPR blends allow for
Figure 2: Mechanical properties of upcycled polyamide 66 (red) produced with Bruggolen TP-M1417 compared with a standard virgin injection moulding grade (grey) of the same viscosity Source: BrüggemannPP modification
66 COMPOUNDING WORLD | July 2018
sterilisation under ethylene oxide, gamma radiation and steam at 121°C. Kraton MD1646 can also be used as an impact modifier to improve PPR toughness in non-medical applications. “Its compatibility with PPR and high rubber content enables higher efficiency than many other impact modifiers without losing transparency,” says Kraton. “The high efficiency also allows a minimum drop in stiffness.” Alternatives to PVC have been on the agenda at recent medical tubing and fluid bag conferences
www.compoundingworld.com
Notched Izod Impact Strength (103
J/m)
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