Flame Retardant Formulations of Long Glass Fiber Reinforced Polypropylene

Long glass fiber reinforced polypropylene (LGFPP) composite has excellent mechanical properties, good dimensional stability and high temperature resistance. It is considered to be an excellent material for replacing steel with plastic in the future. It can be used in automobiles, household appliances, tools, furniture, electronic and electrical fields, etc. Compared with the traditional short fiber reinforced composites, the long fiber reinforced thermoplastic composites have better comprehensive properties.

 

However, the limit oxygen index (LOI) of LGFPP is low, it is easy to burn, and the combustion process has a large amount of heat, which brings great fire hazards.

The flame retardant modification of LGFPP has important research value and practical application significance.

This article recommends two flame retardant LGFPP formulations.

 

Intumescent flame retardant LGFPP

Guizhou University, China National complex modified Polymer Engineering Center and others used pentaerythritol phosphate (PEPA) and melamine polyphosphate (MPP) as intumescent flame retardants (IFR) to flame retardant LGFPP composites. The composite of sepiolite (SP) and IFR was used as a synergistic flame retardant for LGFPP composites.

 

1. Formula

PP：45～70％；

LGF：30%；

IFR: 0～22％，PEPA／MPP =11／9；

SP：0～3％

 

2. Process

3. Flame retardant effect

Table 1  LOI and Combustion Grade of LFGPP Flame retardant Composites with different content of IFR

IFR mass fraction / %	LOI / %	Drip or not	Vertical combustion grade
0	19.2 ± 0.1	NO	1）
16	23.9 ± 0.2	NO	V-2
18	25.2 ± 0.1	NO	V-1
20	26.1 ± 0.3	NO	V-1
22	28.8 ± 0.2	NO	V-0

Note: 1) indicates that no combustion grade has been obtained.

When the mass fraction of IFR is 22%, the effect of adding SP is as shown in Table 2.

 

Table 2   LOI and vertical combustion grades of various composite systems under different SP content

System	LOI / %	Drip or not	Vertical combustion grade
LGFPP	19.2 ± 0.10	NO	---
LGFPP / IFR	28.8 ± 0.15	NO	V-0
LGFPP / IFR / SP1	29.6 ± 0.10	NO	V-0
LGFPP / IFR / SP2	28.1 ± 0.12	NO	V-0
LGFPP / IFR / SP3	27.2 ± 0.11	NO	V-1

Note: SP1, SP2 and SP3 respectively indicate that the mass fraction of SP is 1%, 2%, 3%.

 

4. Changes in mechanical properties

The mechanical properties of the composites decreased after the addition of IFR, and further decreased after the addition of SP.

The mechanical properties of the system with 1% SP content are relatively high. The tensile strength, flexural strength and notched impact strength of the system are reduced by 20.46%, 12.06% and 10.65%, respectively, compared with the flame retardant composite system of LGFPP/IFR.

 

Formulation 2  Bromine/ antimony flame retardant LGFPP